From 32c398f27de8cd5b1478ef60d247c13705b6b50f Mon Sep 17 00:00:00 2001
From: Guilhem <guilhemlemouel@gmail.com>
Date: Wed, 8 Jul 2026 16:34:13 +0200
Subject: [PATCH] feat(sessions): scoped preview refresh + multi-target live
 editors + pipeline preview (#10006)
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* perf(sessions): scope preview-tab refresh to items a chat tool touched

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(sessions): drop dead editor pane, scope raw-app reload by path

Multi-target migration P0. SessionWrapper's inline editor pane was dead (the sessions page always mounts it with hideEditor); remove it and the single-target machinery (setSessionTarget/pickEditorTarget/target-keyed editor views). Scope the raw-app file/runnable preview reload to args.path (the app's workspace path) instead of the session target.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(sessions): back editor state with per-(kind,path) cells

Multi-target migration P1. Replace the three per-kind singleton stores/slots with per-(kind,path) cell maps, created on demand and kept (eviction deferred to P3). The runtime's public interface is unchanged: the flowStore/scriptStore/savedScript/rawApp/... getters and slot(kind) now forward to the 'active cell' per kind (a single-target shim, tracked by activePath, removed in P2 when the UI mounts one editor per tab). loadFlow/loadScript/loadRawApp and syncPreviewWithDeployed operate on the resolved cell; load logic and semantics are otherwise unchanged, so loading one item no longer clobbers another's state.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(sessions): mount every editable preview tab as its own live editor

Multi-target migration P2 — the behavioral flip. resolvePreviewTab no longer takes a target: any editable route (script/flow/raw_app) resolves to an in-process editor, so several items are live at once (iframes remain only for real pages and regular non-raw apps). Each editor binds its own per-(kind,path) cell; the draft codecs close over that cell's store so two editors never cross-write. The single-target shim (activePath + the flowStore/scriptStore/... getters + slot(kind)) is removed; runtime exposes flowCell/scriptCell/rawAppCell(path). Tab open/navigate dedupe by (kind,path) and no longer setTarget. setLiveEditorDraft is gated on the visible tab (isActiveTab) so N editors don't clobber the one-per-(workspace,kind) live-draft slot (path re-key deferred to P4).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* perf(sessions): evict unreferenced editor cells; drop dead warm-editor LRU

Multi-target migration P3. Bound the per-(kind,path) editor cell maps: pruneEditorCells drops every cell no open preview tab still references, wired to a new onTabsChanged adapter callback fired on each tab-set change — so closing or navigating a tab away from an item reclaims its cell (dedupe keeps <=1 editor tab per item, so a pruned item has no live editor to strand). Also remove the now-dead editorWarmIds/promoteEditorWarm/MAX_WARM_EDITORS warm-editor LRU: its only reader (SessionWrapper.mountEditor) was removed in P0, and mounted editors are already capped per-tab by mountedTabKeys.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(sessions): retire session.target; preview is fully tab-driven

Multi-target migration P4 (final). Remove the session.target field and setSessionTarget: the preview is driven entirely by the tab model now (P2). hydratePreviewTabs no longer seeds a tab from target (saved previewTabs only); openEditorInSession seeds the preview via resetSessionPreviewTabs; normalizeLegacySession drops the retired target field from old records. The setLiveEditorDraft focus gate (isActiveTab, one-per-(workspace,kind)) is kept as-is; a per-path re-key is a possible future refinement, not needed for correctness.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(sessions): describe editor cells as-is, not by their refactor history

Address standards review: AGENTS.md requires comments describe the code as it is, not its drafting history. Drop the 'used to be per-kind singletons' / 'pre-refactor empty editor' / 'now' phrasings from the cell comments.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(sessions): update stale runtime.rawApp.val comments to cell.store

Address spec review: two comments still referenced the removed runtime.rawApp.val accessor; the live code uses the per-cell store now.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(sessions): fix editor-cell comments after main merge

Main's #9993 added svelte-ignore comments describing the old
runtime.savedFlow.val / runtime.rawApp.val singleton bindings. The
multi-target refactor binds each tab's own editor cell (cell.store /
cell.saved), so update the comment text to match; the ownership_invalid_binding
directives themselves remain correct (the targets are still runtime-owned).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(sessions): restore data-pipeline preview as a live editor tab

The multi-target refactor removed the old single-target editor pane —
PipelineEditorView's only mount point — so open_preview(kind="pipeline")
opened nothing, even though the chat tool and system prompt still make it
the first step of pipeline authoring.

Route a /pipeline/<folder> preview tab to the in-process graph editor:
- previewRouter: parsePipelineRoute + resolvePreviewTab map the folder to a
  pipeline editor slot; PreviewSlot.editorKind gains 'pipeline'.
- previewTargetForSessionTarget('pipeline') returns the folder route target
  (was undefined); open() keeps a single pipeline tab and retargets it to the
  requested folder, since all pipeline tabs share one runtime.pipelineEditorState.
- PreviewTabHost mounts PipelineEditorView for the pipeline slot.
- PipelineEditorView gains an `active` prop; AI-helper registration and the
  live-badge poll now gate on isActiveSession && active.

Register the pipeline tools on the session's own chat, not the singleton:
PreviewTabHost mounts the view outside the SessionWrapper subtree that
provides the scoped aiChatManager context, so getAiChatManager() fell back to
the app-wide singleton — build_pipeline_node / edit_pipeline_node never
reached the session chat and the model fell back to write_script (whose draft
never appears on the canvas). Use runtime.manager directly instead.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(sessions): scope list-page preview refresh to the page each tool changes

The scoped-refresh pass reloaded every open list-page preview tab on any
workspace mutation (reloadPages: boolean), so creating a schedule also
refreshed the Resources / Variables tabs.

Replace the blanket flag with the specific page paths each tool can change:
write_schedule → /schedules, write_resource → /resources, write_variable →
/variables, create_folder → /folders, write_trigger → the trigger kind's page;
delete/deploy/discard/rebase map their `type` to its page (none for
script/flow/app). Item-editor writes now reload no pages — their live editor
self-syncs. reloadTabs refreshes a list-page tab only when its own path is in
the touched set.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(sessions): drop the inert item-reload path; extract a tested previewReload module

Post multi-target, every editable item is a live editor whose reload() no-ops,
and the one iframe item kind (legacy drag-drop apps) is never emitted as a
scope — so the whole `scopes` half of the preview-reload machinery could never
fire. Remove it (PreviewKind, PreviewScope, scopeKey, itemTypeToPreviewKind,
pendingScopes, and the item-route branch of reloadTabs); the `pages` path
already covers every real reload.

Lift the surviving pure logic out of the 900-line route component into
previewReload.ts — toolReloadEffect(name,args) -> {pages} and a new
tabsToReload(tabs,pages) mirroring selectPreviewTabsToClose — and cover it with
previewReload.test.ts (per-tool page mapping, item kinds reload nothing, the
unknown/local-tool silent-stale guard, loc-over-url matching).

Also clear session.target leftovers: delete the unread EDITOR_TARGET_KINDS
export and rewrite five comments that still described the removed single-target
pane / target-record write.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(sessions): state the preview-reload self-sync invariant once

Consolidate the "live editors self-sync, only list pages reload" rationale
to previewReload.ts and drop the drafting-history phrasings the review
flagged: the update_user_instructions incident and the "(not the runtime)"
contrast in sessionDraftCodecs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(sessions): follow the editor cell when a live tab retargets

Address PR review findings on the multi-target preview.

P1 (Codex) — draft sync stayed bound to the old cell after an in-place tab
retarget. useUserDraftSync captured `codec` once, but navigate() re-points a
live editor tab (script/flow/raw_app) to another item without remounting, so
path/workspace/ready followed the new item while the codec still read/wrote the
previous cell's store — cross-writing drafts. Make `codec` a reactive getter
like the hook's other inputs; SessionEditorTarget rebuilds it per path.

P2 (Claude) — navigate() now enforces the single-pipeline-tab invariant that
open() does: retargeting to a /pipeline/<folder> route focuses and re-points the
existing pipeline tab instead of turning the active tab into a second editor
racing the shared pipelineEditorState.

P2 (Claude) — the deploy-in-session handler peeked an editor slot via the
create-on-miss cell accessors, allocating an empty cell for items with no open
tab. Add a non-creating runtime.loadedEditorPath(kind, path) and use it.

P2 (Claude) — correct a SessionPicker comment left stale by the session.target
removal (the preview no longer seeds from a target).

Tests: two navigate() pipeline-invariant cases. npm run check 0 errors; 167
session unit tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 .../components/sessions/FlowEditorView.svelte |  31 +-
 .../sessions/PipelineEditorView.svelte        |  43 +-
 .../components/sessions/PreviewTabHost.svelte |  31 +-
 .../sessions/RawAppEditorView.svelte          |  41 +-
 .../sessions/ScriptEditorView.svelte          |  24 +-
 .../sessions/SessionEditorTarget.svelte       |  44 +-
 .../components/sessions/SessionPicker.svelte  |   4 +-
 .../components/sessions/SessionWrapper.svelte | 170 +-------
 .../lib/components/sessions/appDraftCodec.ts  |   6 +-
 .../components/sessions/previewReload.test.ts |  87 ++++
 .../lib/components/sessions/previewReload.ts  |  75 ++++
 .../components/sessions/previewRouter.test.ts |  41 +-
 .../lib/components/sessions/previewRouter.ts  |  34 +-
 .../sessions/sessionDraftCodecs.test.ts       |  15 +-
 .../components/sessions/sessionDraftCodecs.ts |  36 +-
 .../sessions/sessionPreviewTabs.svelte.ts     | 134 ++++---
 .../sessions/sessionPreviewTabs.test.ts       | 127 +++---
 .../sessions/sessionRuntime.svelte.ts         | 379 ++++++++++--------
 .../sessions/sessionState.svelte.ts           |  40 +-
 .../sessions/sessionStateIndexedDb.test.ts    |   2 -
 .../sessions/sessionSwitch.svelte.ts          |  17 +-
 .../sessions/useUserDraftSync.svelte.ts       |  18 +-
 .../(root)/(logged)/sessions/+page.svelte     |  78 ++--
 23 files changed, 789 insertions(+), 688 deletions(-)
 create mode 100644 frontend/src/lib/components/sessions/previewReload.test.ts
 create mode 100644 frontend/src/lib/components/sessions/previewReload.ts

diff --git a/frontend/src/lib/components/sessions/FlowEditorView.svelte b/frontend/src/lib/components/sessions/FlowEditorView.svelte
index 45163cc416..fe1ae268d7 100644
--- a/frontend/src/lib/components/sessions/FlowEditorView.svelte
+++ b/frontend/src/lib/components/sessions/FlowEditorView.svelte
@@ -15,7 +15,8 @@
 		path,
 		workspaceId,
 		onNavigate,
-		isActiveSession = true
+		isActiveSession = true,
+		active = true
 	}: {
 		runtime: SessionRuntime
 		path: string
@@ -24,8 +25,12 @@
 		/** Forwarded to SessionEditorTarget — only the visible session claims the
 		 * workspace's single live-editor slot. */
 		isActiveSession?: boolean
+		/** Whether this is the visible preview tab (forwarded as isActiveTab). */
+		active?: boolean
 	} = $props()
 
+	// This tab's own flow cell; each open flow editor binds its own store.
+	const cell = $derived(runtime.flowCell(path))
 	let selectedId = $state('settings-metadata')
 	let diffDrawer: DiffDrawer | undefined = $state()
 
@@ -35,7 +40,7 @@
 	// baseline — useUserDraftSync's inbound effect then syncs the editor preview.
 	// Mirrors ScriptEditorView.
 	async function restoreDeployed() {
-		const saved = runtime.savedFlow.val
+		const saved = cell.saved.val
 		if (!saved) {
 			sendUserToast('Could not restore to deployed', true)
 			return
@@ -61,7 +66,7 @@
 	}
 </script>
 
-{#if runtime.savedFlow.val}
+{#if cell.saved.val}
 	<DiffDrawer bind:this={diffDrawer} {restoreDeployed} isFlow />
 {/if}
 <SessionEditorTarget
@@ -71,7 +76,8 @@
 	{workspaceId}
 	{onNavigate}
 	{isActiveSession}
-	effectivePath={() => runtime.flowStore.val?.path ?? path}
+	isActiveTab={active}
+	effectivePath={() => cell.store.val?.path ?? path}
 >
 	{#snippet editor()}
 		<!-- customUi hides the in-editor "Flow AI Chat" button: the session already
@@ -83,20 +89,21 @@
 		     its intended name in `draft_path`; seed the builder from `draft_path`
 		     (as the full-page editor does) so the Path widget and deploy use the
 		     friendly name rather than creating a flow literally named draft_<uuid>. -->
-		<!-- bind:savedFlow targets runtime.savedFlow.val, reactive state owned by the
-		     SessionRuntime class (created in createRuntime), not by a component
-		     ancestor — so Svelte's ownership check flags a false positive here. -->
+		<!-- bind:savedFlow / flowStore target this tab's editor cell (cell.saved /
+		     cell.store), reactive state owned by the SessionRuntime class (via
+		     flowCell), not by a component ancestor — so Svelte's ownership check
+		     flags a false positive here. -->
 		<!-- svelte-ignore ownership_invalid_binding -->
 		<FlowBuilder
-			flowStore={runtime.flowStore}
-			flowStateStore={runtime.flowStateStore}
-			initialPath={(runtime.savedFlow.val as any)?.draft_path ?? path}
+			flowStore={cell.store}
+			flowStateStore={cell.stateStore}
+			initialPath={(cell.saved.val as any)?.draft_path ?? path}
 			autosaveWorkspace={workspaceId}
 			autosavePath={path}
-			newFlow={!runtime.savedFlow.val || runtime.savedFlow.val.no_deployed === true}
+			newFlow={!cell.saved.val || cell.saved.val.no_deployed === true}
 			{selectedId}
 			loading={false}
-			bind:savedFlow={runtime.savedFlow.val}
+			bind:savedFlow={cell.saved.val}
 			{diffDrawer}
 			{onNavigate}
 			customUi={{ topBar: { aiBuilder: false } }}
diff --git a/frontend/src/lib/components/sessions/PipelineEditorView.svelte b/frontend/src/lib/components/sessions/PipelineEditorView.svelte
index 0e3be64e36..0e30d0959d 100644
--- a/frontend/src/lib/components/sessions/PipelineEditorView.svelte
+++ b/frontend/src/lib/components/sessions/PipelineEditorView.svelte
@@ -4,7 +4,6 @@
 	import { Loader2, Workflow } from 'lucide-svelte'
 	import PipelineGraphEditor from '$lib/components/assets/AssetGraph/PipelineGraphEditor.svelte'
 	import PipelineTriggerEditors from '$lib/components/assets/AssetGraph/PipelineTriggerEditors.svelte'
-	import { getAiChatManager } from '$lib/components/copilot/chat/aiChatManagerContext'
 	import { resolveGraph } from '$lib/components/assets/AssetGraph/resolveGraph'
 	import { useActiveRunnableIds } from '$lib/components/assets/AssetGraph/activeRunnables.svelte'
 	import type {
@@ -21,7 +20,8 @@
 		runtime,
 		path,
 		workspaceId,
-		isActiveSession = true
+		isActiveSession = true,
+		active = true
 	}: {
 		/** Per-session runtime; owns the pipeline editor state so it survives the
 		 * editor pane unmounting on hide/show. */
@@ -31,10 +31,22 @@
 		workspaceId: string
 		/** Only the visible session registers the pipeline tools on its manager. */
 		isActiveSession?: boolean
+		/** Whether this is the foreground preview tab. */
+		active?: boolean
 	} = $props()
 
-	// The session's scoped chat manager (falls back to the singleton off-session).
-	const aiChatManager = getAiChatManager()
+	// This session's own chat manager — used directly rather than via
+	// getAiChatManager()'s context lookup: PreviewTabHost mounts this view in the
+	// preview panel, outside the SessionWrapper subtree that provides the scoped
+	// manager context, so a lookup would fall back to the app-wide singleton and
+	// register the pipeline tools (build_pipeline_node / edit_pipeline_node) on the
+	// wrong chat — leaving this session's chat unable to build canvas nodes.
+	const aiChatManager = runtime.manager
+
+	// Only the foreground tab of the foreground session owns the chat's pipeline
+	// tools and runs the live-badge poll — a background tab (another preview tab is
+	// showing, or another session is active) must not shadow that context or poll.
+	const engaged = $derived(isActiveSession && active)
 
 	// Externalized editor state — lives on the runtime so the drafts persist across
 	// hide/show of the preview pane (the pane unmounts on hide).
@@ -55,10 +67,10 @@
 					activeRunnableJobId = undefined
 					// Re-scope the Global pipeline prompt to the new folder (the helper
 					// methods already read the reactive path, but the system message
-					// string was built for the old one). Only when this session is the
-					// active one — its helpers are the registered set; a hidden session
-					// reconfigures when it next becomes active.
-					if (isActiveSession) aiChatManager.rebuildGlobalSystemMessage()
+					// string was built for the old one). Only when this tab is engaged —
+					// its helpers are the registered set; a background tab reconfigures
+					// when it next becomes the foreground one.
+					if (engaged) aiChatManager.rebuildGlobalSystemMessage()
 				}
 				pe.folder = folder
 			}
@@ -210,9 +222,9 @@
 	let activeRunnableJobId = $state<string | undefined>(undefined)
 	$effect(() => {
 		pathPrefix // re-scope the poll when the folder changes
-		// Only the visible session needs live badges/event-log; hidden warm panes
-		// (up to MAX_WARM_EDITORS) shouldn't poll in the background.
-		activeRunnables.setObserving(isActiveSession)
+		// Only the engaged (foreground) tab needs live badges/event-log; a
+		// background tab or a hidden session shouldn't poll.
+		activeRunnables.setObserving(engaged)
 		return () => activeRunnables.dispose()
 	})
 	$effect(() => {
@@ -270,11 +282,12 @@
 		}
 	}
 
-	// Register the pipeline tools on this session's manager while the view is the
-	// active one. setPipelineHelpers rebuilds the global tool set to include the
-	// pipeline tools and tears them down on cleanup.
+	// Register the pipeline tools on this session's manager while this tab is the
+	// engaged (foreground) one. setPipelineHelpers rebuilds the global tool set to
+	// include the pipeline tools and tears them down on cleanup — so switching to
+	// another preview tab or session releases them.
 	$effect(() => {
-		if (!isActiveSession) return
+		if (!engaged) return
 		return aiChatManager.setPipelineHelpers(helpers)
 	})
 </script>
diff --git a/frontend/src/lib/components/sessions/PreviewTabHost.svelte b/frontend/src/lib/components/sessions/PreviewTabHost.svelte
index 81ad9e525e..2a25cff3a5 100644
--- a/frontend/src/lib/components/sessions/PreviewTabHost.svelte
+++ b/frontend/src/lib/components/sessions/PreviewTabHost.svelte
@@ -13,6 +13,7 @@
 	import ScriptEditorView from './ScriptEditorView.svelte'
 	import FlowEditorView from './FlowEditorView.svelte'
 	import RawAppEditorView from './RawAppEditorView.svelte'
+	import PipelineEditorView from './PipelineEditorView.svelte'
 
 	let {
 		tab,
@@ -33,15 +34,16 @@
 		mounted: boolean
 		/** Short tab label, for the iframe title. */
 		label: string
-		/** A link click inside a live editor re-points the session target + tab. */
+		/** A link click inside a live editor re-points the active preview tab. */
 		onNavigate: (item: WorkspaceItem) => void
 		/** Iframe finished loading — the page reads back its observed location. */
 		onLoad: (frame: HTMLIFrameElement) => void
 	} = $props()
 
-	// Editor vs iframe is decided purely from the tab URL + the session's target
-	// (see resolvePreviewTab). Only the target tab of a wrappable kind goes live.
-	const slot = $derived(resolvePreviewTab(tab.url, session?.target))
+	// Editor vs iframe is decided purely from the tab URL (see resolvePreviewTab):
+	// any editable item (script/flow/raw app) or a pipeline folder mounts its own
+	// live editor.
+	const slot = $derived(resolvePreviewTab(tab.url))
 	const workspaceId = $derived(
 		session ? (getEffectiveWorkspaceId(session) ?? $workspaceStore ?? '') : ''
 	)
@@ -80,7 +82,14 @@
 {#if slot.kind === 'editor' && mounted && runtime}
 	<div class="absolute inset-0 flex flex-col min-h-0 bg-surface {visibility}" aria-hidden={!active}>
 		{#if slot.editorKind === 'flow'}
-			<FlowEditorView {runtime} path={slot.path} {workspaceId} {onNavigate} {isActiveSession} />
+			<FlowEditorView
+				{runtime}
+				path={slot.path}
+				{workspaceId}
+				{onNavigate}
+				{isActiveSession}
+				{active}
+			/>
 		{:else if slot.editorKind === 'script'}
 			<ScriptEditorView
 				{runtime}
@@ -88,10 +97,20 @@
 				{workspaceId}
 				{onNavigate}
 				{isActiveSession}
+				{active}
 				initialTestPanelCollapsed
 			/>
+		{:else if slot.editorKind === 'pipeline'}
+			<PipelineEditorView {runtime} path={slot.path} {workspaceId} {isActiveSession} {active} />
 		{:else}
-			<RawAppEditorView {runtime} path={slot.path} {workspaceId} {onNavigate} {isActiveSession} />
+			<RawAppEditorView
+				{runtime}
+				path={slot.path}
+				{workspaceId}
+				{onNavigate}
+				{isActiveSession}
+				{active}
+			/>
 		{/if}
 	</div>
 {:else if mounted}
diff --git a/frontend/src/lib/components/sessions/RawAppEditorView.svelte b/frontend/src/lib/components/sessions/RawAppEditorView.svelte
index c3ad7ead4e..cb6507519c 100644
--- a/frontend/src/lib/components/sessions/RawAppEditorView.svelte
+++ b/frontend/src/lib/components/sessions/RawAppEditorView.svelte
@@ -17,7 +17,8 @@
 		path,
 		workspaceId,
 		onNavigate,
-		isActiveSession = true
+		isActiveSession = true,
+		active = true
 	}: {
 		runtime: SessionRuntime
 		path: string
@@ -26,13 +27,17 @@
 		/** Forwarded to SessionEditorTarget — only the visible session claims the
 		 * workspace's single live-editor slot. */
 		isActiveSession?: boolean
+		/** Whether this is the visible preview tab (forwarded as isActiveTab). */
+		active?: boolean
 	} = $props()
 
+	// This tab's own raw-app cell; each open app editor binds its own store.
+	const cell = $derived(runtime.rawAppCell(path))
 	let diffDrawer: DiffDrawer | undefined = $state()
 
 	// Path typed in the editor header, surfaced when it differs from the stored
 	// path. Mirror it into the runtime draft as `draft_path` so the rename
-	// mutates runtime.rawApp.val → the autosave sig changes → the draft is saved
+	// mutates this cell's store → the autosave sig changes → the draft is saved
 	// (and the home/review/Drafts lists show the friendly name). Mirrors the
 	// full-page /apps_raw/edit route.
 	let pendingDraftPath = $state<string | undefined>(undefined)
@@ -45,7 +50,7 @@
 	$effect(() => {
 		const dp = pendingDraftPath
 		untrack(() => {
-			const val = runtime.rawApp.val
+			const val = cell.store.val
 			if (!val) return
 			if (dp !== undefined) {
 				surfacedDraftPath = true
@@ -80,7 +85,7 @@
 	}
 </script>
 
-{#if runtime.savedRawApp.val}
+{#if cell.saved.val}
 	<DiffDrawer bind:this={diffDrawer} {restoreDeployed} />
 {/if}
 <SessionEditorTarget
@@ -90,31 +95,33 @@
 	{workspaceId}
 	{onNavigate}
 	{isActiveSession}
-	effectivePath={() => runtime.rawApp.val?.path ?? path}
+	isActiveTab={active}
+	effectivePath={() => cell.store.val?.path ?? path}
 >
 	{#snippet editor()}
-		{#if runtime.rawApp.val}
+		{#if cell.store.val}
 			<!-- newApp: a draft-only app (no_deployed=true) has a truthy synthesized
 			     savedApp but no deployed row, so it must deploy via createApp — keying
 			     on !savedApp alone would updateApp a never-deployed path and 404
 			     "not found". -->
-			<!-- These bind: targets live on runtime.rawApp.val, reactive state owned by
-			     the SessionRuntime class (created in createRuntime), not by a component
-			     ancestor — so Svelte's ownership check flags a false positive here. -->
+			<!-- These bind: targets live on this tab's editor cell (cell.store.val /
+			     cell.saved.val), reactive state owned by the SessionRuntime class (via
+			     rawAppCell), not by a component ancestor — so Svelte's ownership check
+			     flags a false positive here. -->
 			<!-- svelte-ignore ownership_invalid_binding -->
 			<RawAppEditor
-				bind:files={runtime.rawApp.val.files}
-				bind:runnables={runtime.rawApp.val.runnables}
-				bind:data={runtime.rawApp.val.data}
-				bind:summary={runtime.rawApp.val.summary}
+				bind:files={cell.store.val.files}
+				bind:runnables={cell.store.val.runnables}
+				bind:data={cell.store.val.data}
+				bind:summary={cell.store.val.summary}
 				bind:pendingDraftPath
-				newPath={runtime.rawApp.val.draft_path ?? runtime.rawApp.val.path}
+				newPath={cell.store.val.draft_path ?? cell.store.val.path}
 				{path}
 				autosaveWorkspace={workspaceId}
 				autosavePath={path}
-				policy={runtime.rawApp.val.policy}
-				bind:savedApp={runtime.savedRawApp.val}
-				newApp={!runtime.savedRawApp.val || runtime.savedRawApp.val.no_deployed === true}
+				policy={cell.store.val.policy}
+				bind:savedApp={cell.saved.val}
+				newApp={!cell.saved.val || cell.saved.val.no_deployed === true}
 				{diffDrawer}
 				{onNavigate}
 				onResetToDeployed={reloadDeployed}
diff --git a/frontend/src/lib/components/sessions/ScriptEditorView.svelte b/frontend/src/lib/components/sessions/ScriptEditorView.svelte
index 563ddf9e55..d286917667 100644
--- a/frontend/src/lib/components/sessions/ScriptEditorView.svelte
+++ b/frontend/src/lib/components/sessions/ScriptEditorView.svelte
@@ -16,7 +16,8 @@
 		workspaceId,
 		onNavigate,
 		initialTestPanelCollapsed = false,
-		isActiveSession = true
+		isActiveSession = true,
+		active = true
 	}: {
 		runtime: SessionRuntime
 		path: string
@@ -26,8 +27,12 @@
 		/** Forwarded to SessionEditorTarget — only the visible session claims the
 		 * workspace's single live-editor slot. */
 		isActiveSession?: boolean
+		/** Whether this is the visible preview tab (forwarded as isActiveTab). */
+		active?: boolean
 	} = $props()
 
+	// This tab's own script cell; each open script editor binds its own store.
+	const cell = $derived(runtime.scriptCell(path))
 	let diffDrawer: DiffDrawer | undefined = $state()
 
 	// Restore actions for the diff drawer. The previous shared
@@ -36,7 +41,7 @@
 	// reset the live UserDraft handle to the target baseline — the inbound
 	// effect then syncs the editor preview. Mirrors /scripts/edit's restore.
 	async function restoreDeployed() {
-		const saved = runtime.savedScript.val
+		const saved = cell.saved.val
 		if (!saved) {
 			sendUserToast('Could not restore to deployed', true)
 			return
@@ -71,7 +76,7 @@
 	}
 </script>
 
-{#if runtime.savedScript.val}
+{#if cell.saved.val}
 	<DiffDrawer bind:this={diffDrawer} {restoreDeployed} />
 {/if}
 <SessionEditorTarget
@@ -81,10 +86,11 @@
 	{workspaceId}
 	{onNavigate}
 	{isActiveSession}
-	effectivePath={() => runtime.scriptStore.val?.path ?? path}
+	isActiveTab={active}
+	effectivePath={() => cell.store.val?.path ?? path}
 >
 	{#snippet editor()}
-		{#if runtime.scriptStore.val}
+		{#if cell.store.val}
 			<!--
 				A script with no backend version yet (AI-created, never saved or deployed
 				→ savedScript undefined) is a *new* script: pass an empty initialPath so
@@ -94,14 +100,14 @@
 				edit mode (Save draft + Diff) without navigating away.
 			-->
 			<ScriptBuilder
-				bind:script={runtime.scriptStore.val}
-				bind:savedScript={runtime.savedScript.val}
-				initialPath={runtime.savedScript.val ? path : ''}
+				bind:script={cell.store.val}
+				bind:savedScript={cell.saved.val}
+				initialPath={cell.saved.val ? path : ''}
 				autosaveWorkspace={workspaceId}
 				autosavePath={path}
 				initialPathChosen={true}
 				neverShowMeta={true}
-				fullyLoaded={!runtime.slot('script').loading}
+				fullyLoaded={!cell.slot.loading}
 				disableHistoryChange={true}
 				{diffDrawer}
 				{onNavigate}
diff --git a/frontend/src/lib/components/sessions/SessionEditorTarget.svelte b/frontend/src/lib/components/sessions/SessionEditorTarget.svelte
index 5b9ac237a1..ce1fd38221 100644
--- a/frontend/src/lib/components/sessions/SessionEditorTarget.svelte
+++ b/frontend/src/lib/components/sessions/SessionEditorTarget.svelte
@@ -16,7 +16,8 @@
 		effectivePath,
 		editor,
 		onNavigate,
-		isActiveSession = true
+		isActiveSession = true,
+		isActiveTab = true
 	}: {
 		runtime: SessionRuntime
 		kind: SessionTargetKind
@@ -31,12 +32,14 @@
 		/** The heavy editor for this kind; remounted on a data-ready target swap. */
 		editor: Snippet
 		onNavigate?: (item: WorkspaceItem) => void
-		/**
-		 * Only the visible session claims the workspace's single live-editor slot
-		 * (one per (workspace, kind)); a warm-but-hidden session must not, else
-		 * chat actions on the visible session resolve to the hidden one's path.
-		 */
+		/** A warm-but-hidden session must not claim the live-editor slot. */
 		isActiveSession?: boolean
+		/**
+		 * Only the visible editor tab claims the workspace's single live-editor slot
+		 * (one per (workspace, kind)); with several editors open at once, a hidden
+		 * tab must not, else chat actions resolve to the wrong item's path.
+		 */
+		isActiveTab?: boolean
 	} = $props()
 
 	// Mark this subtree as the session side panel: editors below detect the
@@ -47,7 +50,15 @@
 	// rely on its presence, not its identity.
 	setContext('aiChatManager', runtime.manager)
 
-	const slot = $derived(runtime.slot(kind))
+	// This tab's own editor cell (per (kind, path)); several tabs can be live at once.
+	const cell = $derived(
+		kind === 'flow'
+			? runtime.flowCell(path)
+			: kind === 'script'
+				? runtime.scriptCell(path)
+				: runtime.rawAppCell(path)
+	)
+	const slot = $derived(cell.slot)
 
 	function triggerLoad(): Promise<void> {
 		if (kind === 'flow') return runtime.loadFlow(workspaceId, path)
@@ -56,10 +67,15 @@
 	}
 
 	function buildCodec(): DraftSyncCodec<any> {
-		if (kind === 'flow') return makeFlowCodec(runtime)
-		if (kind === 'script') return makeScriptCodec(runtime, () => path)
-		return makeRawAppCodec(runtime)
+		if (kind === 'flow')
+			return makeFlowCodec(runtime.flowCell(path).store, runtime.flowCell(path).stateStore)
+		if (kind === 'script') return makeScriptCodec(runtime.scriptCell(path).store, () => path)
+		return makeRawAppCodec(runtime.rawAppCell(path).store)
 	}
+	// Rebuilds when `path` changes so the sync always binds this tab's current
+	// cell: retargeting the tab (in-editor link / breadcrumb) swaps `path` without
+	// remounting, and each codec closes over one cell's store.
+	const codec = $derived(buildCodec())
 
 	$effect(() => {
 		if (workspaceId && path) {
@@ -69,11 +85,11 @@
 
 	// Mark this editor as the live editor draft for the session's workspace so
 	// the chat's `isLiveDraft` hint / `discard_local_draft` tool resolve to this
-	// path — same registration the regular edit pages do. Gated on
-	// `isActiveSession` (see prop doc).
+	// path — same registration the regular edit pages do. Only the visible tab of
+	// the active session claims the (workspace, kind) slot (see prop docs).
 	$effect(() => {
 		if (!workspaceId || !path) return
-		if (!isActiveSession) return
+		if (!isActiveSession || !isActiveTab) return
 		UserDraft.setLiveEditorDraft({
 			workspace: workspaceId,
 			itemKind: kind,
@@ -87,7 +103,7 @@
 		path: () => path,
 		workspace: () => workspaceId,
 		ready: () => slot.loadedPath === path,
-		codec: buildCodec()
+		codec: () => codec
 	})
 
 	// Debounced loading affordance for a breadcrumb swap: while the loaded path
diff --git a/frontend/src/lib/components/sessions/SessionPicker.svelte b/frontend/src/lib/components/sessions/SessionPicker.svelte
index ae97510629..e3d1c5d21e 100644
--- a/frontend/src/lib/components/sessions/SessionPicker.svelte
+++ b/frontend/src/lib/components/sessions/SessionPicker.svelte
@@ -311,8 +311,8 @@
 		// A new session opened from a Windmill page adopts that page as its first
 		// preview tab (resetSessionPreviewTabs handles a reused transient whose
 		// tabs still show a previous destination). Skip when already on the
-		// sessions page (nothing meaningful to capture) so the preview seeds from
-		// the session's editor target (or stays empty) instead.
+		// sessions page (nothing meaningful to capture) so the preview starts
+		// empty until the chat opens something.
 		if (!onSessionsPage) {
 			const url = page.url.pathname + page.url.search
 			resetSessionPreviewTabs(fresh.id, url)
diff --git a/frontend/src/lib/components/sessions/SessionWrapper.svelte b/frontend/src/lib/components/sessions/SessionWrapper.svelte
index 8161349656..f5fa09c6d0 100644
--- a/frontend/src/lib/components/sessions/SessionWrapper.svelte
+++ b/frontend/src/lib/components/sessions/SessionWrapper.svelte
@@ -19,21 +19,12 @@
 		ArrowUpRight,
 		EllipsisVertical,
 		ExternalLink,
-		PanelRightClose,
-		PanelRightOpen,
 		Pencil,
 		Settings,
 		Trash2
 	} from 'lucide-svelte'
 	import { type Item } from '$lib/utils'
 	import WorkspaceScopeTrigger from '$lib/components/WorkspaceScopeTrigger.svelte'
-	import type { WorkspaceItem } from '$lib/components/workspacePicker'
-	import Popover from '$lib/components/meltComponents/Popover.svelte'
-	import WorkspaceItemDrillPicker from '$lib/components/WorkspaceItemDrillPicker.svelte'
-	import FlowEditorView from './FlowEditorView.svelte'
-	import ScriptEditorView from './ScriptEditorView.svelte'
-	import RawAppEditorView from './RawAppEditorView.svelte'
-	import PipelineEditorView from './PipelineEditorView.svelte'
 	import SessionWorkspaceBar from './SessionWorkspaceBar.svelte'
 	import SessionChangesBar from './SessionChangesBar.svelte'
 	import {
@@ -49,37 +40,23 @@
 		selectSession,
 		sessionState,
 		setSessionArchived,
-		setSessionTarget,
-		syncWorkspaceTo,
-		type SessionTarget
+		syncWorkspaceTo
 	} from './sessionState.svelte'
-	import { editorWarmIds, getOrCreateRuntime, removeSession } from './sessionRuntime.svelte'
+	import { getOrCreateRuntime, removeSession } from './sessionRuntime.svelte'
 	import { goto } from '$lib/navigation'
 	import { base } from '$app/paths'
-	import { slide } from 'svelte/transition'
 	import { splitterPointerCapture } from '$lib/utils/splitterPointerCapture'
 
-	// hideEditor: never mount the inline editor pane. Used by the sessions page,
-	// where the edited item is shown in a live page preview (iframe) beside the
-	// chat instead, so the wrapper contributes only its chat column.
 	// headerInset: extra left padding on the chat header so it clears a floating
 	// control (the collapsed-rail launcher) sitting at the screen's top-left.
 	let {
 		sessionId,
-		hideEditor = false,
 		headerInset = false
 	}: {
 		sessionId: string
-		hideEditor?: boolean
 		headerInset?: boolean
 	} = $props()
 
-	// LRU-warm sessions get their editor pane mounted; others render
-	// chat-only. Reading from the reactive Set keeps SessionWrapper in
-	// sync with promoteEditorWarm without an explicit prop round-trip
-	// through the page route.
-	const mountEditor = $derived(editorWarmIds.has(sessionId))
-
 	// Parent keys by sessionId; this wrapper only mounts when the session exists.
 	// Captured at script-init so we can synchronously bind context.
 	const initialSession = sessionState.sessions.find((s) => s.id === sessionId)
@@ -248,43 +225,6 @@
 		runtime?.manager.displayMessages.some((m) => m.role === 'user') ?? false
 	)
 
-	// Effective workspace for routing editor views — committed if set,
-	// otherwise the pending pick, otherwise the current active workspace.
-	const effectiveWorkspaceId = $derived(
-		session ? (getEffectiveWorkspaceId(session) ?? $workspaceStore ?? '') : ''
-	)
-
-	// Core mutation: assign a target via the canonical setter, then re-open
-	// the editor pane. Shared by every code path that swaps the session's
-	// editor target (drill picker, fork-bar dropdown, …).
-	function applyEditorTarget(target: SessionTarget, summary?: string) {
-		if (!session) return
-		setSessionTarget(session.id, target, summary)
-		// Picking a target also re-opens the editor pane (the user just chose
-		// what to view).
-		editorVisible = true
-	}
-
-	function pickEditorTarget(item: WorkspaceItem) {
-		// Legacy drag-and-drop apps aren't hosted in the session preview pane —
-		// open them in the standalone app editor instead. Only code-based raw
-		// apps (item.raw_app) are previewable here.
-		if (item.kind === 'app' && !item.raw_app) {
-			goto(`/apps/edit/${item.path}?workspace=${effectiveWorkspaceId}`)
-			return
-		}
-		// WorkspaceItem.kind is 'flow'|'script'|'app'; any 'app' reaching here is
-		// a raw app. The diff-API uses 'raw_app' as its kind so we align
-		// SessionTarget on the same canonical string.
-		const kind: SessionTarget['kind'] = item.kind === 'app' ? 'raw_app' : item.kind
-		applyEditorTarget({ kind, path: item.path }, item.summary)
-	}
-
-	// Editor pane visibility. Toggling this just hides/shows the pane via CSS
-	// — the editor stays mounted, so re-opening doesn't pay a remount cost
-	// and xy-flow / Monaco keep their viewport state.
-	let editorVisible = $state(true)
-
 	// Focus the chat input whenever this session is the active one.
 	// The textarea is disabled until copilotInfo loads (otherwise focus is
 	// a silent no-op), so we wait for that too. Triggers on initial mount,
@@ -333,13 +273,6 @@
 {#if !session || !runtime}
 	<div class="p-8 text-secondary text-sm">Session not found</div>
 {:else}
-	{@const hasTarget =
-		session.target?.kind === 'flow' ||
-		session.target?.kind === 'script' ||
-		session.target?.kind === 'raw_app' ||
-		session.target?.kind === 'pipeline'}
-	{@const hasEditor = mountEditor && hasTarget && editorVisible && !hideEditor}
-
 	{#snippet inputPreface()}
 		{#if !hasFirstUserMessage}
 			<SessionWorkspaceBar {session} />
@@ -386,11 +319,9 @@
 	     sessions have their own empty-state affordances above. -->
 	{#snippet sessionEmptyHint()}{/snippet}
 
-	<!-- Undefined pane sizes (not an explicit `size`): Splitpanes auto-distributes —
-	     a lone chat pane fills 100%, and when the editor pane mounts the two split
-	     50/50. A reactive `size={hasEditor ? 50 : 100}` here instead races the
-	     sibling pane appearing on reload → "Could not resize panes due to constraints"
-	     and a wrong split. -->
+	<!-- The wrapper contributes only the chat column; edited items are shown in the
+	     page's preview tabs (PreviewTabHost) beside it, not a second pane here. The
+	     single Pane fills 100% (no explicit `size`, so Splitpanes auto-distributes). -->
 	<div class="flex-1 min-h-0 flex flex-col" use:splitterPointerCapture>
 		<Splitpanes horizontal={false} class="flex-1 min-h-0 splitter-hidden">
 			<Pane minSize={25} class="flex flex-col min-h-0 pb-2">
@@ -476,55 +407,6 @@
 							</NameIdTooltip>
 						</div>
 					{/if}
-					{#if !hideEditor && !session.target && hasFirstUserMessage}
-						<!-- Drill-picker for sessions that have started but haven't
-				     picked an editor target yet. Hidden on fresh sessions
-				     (no messages yet) — the workspace bar is the only
-				     header affordance during the empty state. -->
-						<div class="ml-auto">
-							<Popover
-								placement="bottom-end"
-								usePointerDownOutside
-								disableFocusTrap
-								enableFlyTransition
-								class="inline-flex"
-							>
-								{#snippet trigger()}
-									<Button variant="default" unifiedSize="xs" startIcon={{ icon: PanelRightOpen }}>
-										Open editor
-									</Button>
-								{/snippet}
-								{#snippet content()}
-									<WorkspaceItemDrillPicker
-										onPick={(item: WorkspaceItem) => pickEditorTarget(item)}
-									/>
-								{/snippet}
-							</Popover>
-						</div>
-					{:else if !hideEditor && hasTarget && mountEditor && !editorVisible}
-						<div class="ml-auto">
-							<Button
-								variant="subtle"
-								unifiedSize="xs"
-								startIcon={{ icon: PanelRightOpen }}
-								onclick={() => (editorVisible = true)}
-							>
-								Show editor
-							</Button>
-						</div>
-					{:else if hasEditor}
-						<div class="ml-auto flex flex-row items-center gap-1">
-							<button
-								type="button"
-								onclick={() => (editorVisible = false)}
-								title="Close editor"
-								aria-label="Close editor"
-								class="inline-flex items-center justify-center w-6 h-6 rounded text-tertiary hover:text-primary hover:bg-surface-hover"
-							>
-								<PanelRightClose size={14} />
-							</button>
-						</div>
-					{/if}
 				</header>
 				<div class="flex-1 min-h-0 w-full flex flex-col {hasFirstUserMessage ? '' : 'pt-8'}">
 					<AIChat
@@ -545,48 +427,6 @@
 					/>
 				</div>
 			</Pane>
-			{#if hasEditor && session.target}
-				<Pane minSize={30} class="flex flex-col min-h-0 p-2 pl-0">
-					<div
-						transition:slide={{ axis: 'x', duration: 200 }}
-						class="flex flex-col flex-1 min-h-0 rounded-md border border-light overflow-hidden relative"
-					>
-						{#if session.target.kind === 'flow'}
-							<FlowEditorView
-								{runtime}
-								path={session.target.path}
-								workspaceId={effectiveWorkspaceId}
-								onNavigate={pickEditorTarget}
-								isActiveSession={sessionState.currentSessionId === sessionId}
-							/>
-						{:else if session.target.kind === 'script'}
-							<ScriptEditorView
-								{runtime}
-								path={session.target.path}
-								workspaceId={effectiveWorkspaceId}
-								onNavigate={pickEditorTarget}
-								initialTestPanelCollapsed
-								isActiveSession={sessionState.currentSessionId === sessionId}
-							/>
-						{:else if session.target.kind === 'raw_app'}
-							<RawAppEditorView
-								{runtime}
-								path={session.target.path}
-								workspaceId={effectiveWorkspaceId}
-								onNavigate={pickEditorTarget}
-								isActiveSession={sessionState.currentSessionId === sessionId}
-							/>
-						{:else if session.target.kind === 'pipeline'}
-							<PipelineEditorView
-								{runtime}
-								path={session.target.path}
-								workspaceId={effectiveWorkspaceId}
-								isActiveSession={sessionState.currentSessionId === sessionId}
-							/>
-						{/if}
-					</div>
-				</Pane>
-			{/if}
 		</Splitpanes>
 	</div>
 
diff --git a/frontend/src/lib/components/sessions/appDraftCodec.ts b/frontend/src/lib/components/sessions/appDraftCodec.ts
index 5f870be92d..10752b8d8f 100644
--- a/frontend/src/lib/components/sessions/appDraftCodec.ts
+++ b/frontend/src/lib/components/sessions/appDraftCodec.ts
@@ -18,9 +18,9 @@ export type RawAppDraft = {
 	draft_path?: string
 }
 
-// The shape `runtime.rawApp.val` actually holds (see SessionRuntime in
-// sessionRuntime.svelte.ts). Adds `path` (a key, not a draft field) and
-// makes `policy` required for the editor's live binding.
+// The shape a raw-app cell's store (`RawAppRuntimeValue` in
+// sessionRuntime.svelte.ts) actually holds. Adds `path` (a key, not a draft
+// field) and makes `policy` required for the editor's live binding.
 export type RuntimeRawApp = {
 	summary: string
 	path: string
diff --git a/frontend/src/lib/components/sessions/previewReload.test.ts b/frontend/src/lib/components/sessions/previewReload.test.ts
new file mode 100644
index 0000000000..de11805b9a
--- /dev/null
+++ b/frontend/src/lib/components/sessions/previewReload.test.ts
@@ -0,0 +1,87 @@
+import { describe, it, expect } from 'vitest'
+import { toolReloadEffect, tabsToReload } from './previewReload'
+import type { SessionPreviewTab } from './sessionState.svelte'
+
+describe('toolReloadEffect', () => {
+	it('maps a non-item mutation to its own list page only', () => {
+		expect(toolReloadEffect('write_schedule', { path: 'u/me/s' }).pages).toEqual(['/schedules'])
+		expect(toolReloadEffect('write_resource', {}).pages).toEqual(['/resources'])
+		expect(toolReloadEffect('write_variable', {}).pages).toEqual(['/variables'])
+		expect(toolReloadEffect('create_folder', { name: 'f' }).pages).toEqual(['/folders'])
+	})
+
+	it('maps a trigger write to its kind-specific page', () => {
+		expect(toolReloadEffect('write_trigger', { kind: 'kafka' }).pages).toEqual(['/kafka_triggers'])
+		expect(toolReloadEffect('write_trigger', { kind: 'http' }).pages).toEqual(['/routes'])
+	})
+
+	it('maps a generic item tool to the page for its type', () => {
+		expect(toolReloadEffect('deploy_workspace_item', { type: 'schedule' }).pages).toEqual([
+			'/schedules'
+		])
+		expect(toolReloadEffect('delete_workspace_item', { type: 'resource' }).pages).toEqual([
+			'/resources'
+		])
+		expect(
+			toolReloadEffect('discard_local_draft', { type: 'trigger', trigger_kind: 'nats' }).pages
+		).toEqual(['/nats_triggers'])
+	})
+
+	it('reloads no page for item-editor kinds (they self-sync via their live editor)', () => {
+		for (const type of ['script', 'flow', 'app']) {
+			expect(toolReloadEffect('deploy_workspace_item', { type }).pages).toEqual([])
+		}
+		for (const name of [
+			'write_script',
+			'edit_script',
+			'write_flow',
+			'init_app',
+			'write_app_file'
+		]) {
+			expect(toolReloadEffect(name, { path: 'u/me/x' }).pages).toEqual([])
+		}
+	})
+
+	it('reloads nothing for a purely local or unknown tool (the silent-stale guard)', () => {
+		expect(toolReloadEffect('update_user_instructions', {}).pages).toEqual([])
+		expect(toolReloadEffect('some_future_tool', { path: 'p' }).pages).toEqual([])
+	})
+
+	it('reloads nothing for a trigger of unknown kind rather than guessing', () => {
+		expect(toolReloadEffect('write_trigger', { kind: 'not_a_kind' }).pages).toEqual([])
+	})
+})
+
+describe('tabsToReload', () => {
+	const scheduleTab: SessionPreviewTab = { id: 's', url: '/schedules', loc: '/schedules' }
+	const resourceTab: SessionPreviewTab = { id: 'r', url: '/resources', loc: '/resources' }
+	const scriptTab: SessionPreviewTab = {
+		id: 'sc',
+		url: '/scripts/edit/f/foo/bar',
+		loc: '/scripts/edit/f/foo/bar'
+	}
+	const pipelineTab: SessionPreviewTab = { id: 'p', url: '/pipeline/crm', loc: '/pipeline/crm' }
+	const tabs = [scheduleTab, resourceTab, scriptTab, pipelineTab]
+
+	it('returns only the tabs whose page is in the set', () => {
+		expect(tabsToReload(tabs, new Set(['/schedules']))).toEqual([scheduleTab])
+	})
+
+	it('returns list-page tabs but never item-editor or pipeline tabs', () => {
+		// toolReloadEffect only ever emits list-page paths, so item/pipeline route
+		// paths are never in `pages` — those tabs self-sync and stay put.
+		expect(tabsToReload(tabs, new Set(['/schedules', '/resources']))).toEqual([
+			scheduleTab,
+			resourceTab
+		])
+	})
+
+	it('is empty when no pages were touched', () => {
+		expect(tabsToReload(tabs, new Set())).toEqual([])
+	})
+
+	it('matches on the observed loc (with query/hash stripped) over the seeded url', () => {
+		const navigated: SessionPreviewTab = { id: 'n', url: '/runs', loc: '/schedules?workspace=w' }
+		expect(tabsToReload([navigated], new Set(['/schedules']))).toEqual([navigated])
+	})
+})
diff --git a/frontend/src/lib/components/sessions/previewReload.ts b/frontend/src/lib/components/sessions/previewReload.ts
new file mode 100644
index 0000000000..82a87285e1
--- /dev/null
+++ b/frontend/src/lib/components/sessions/previewReload.ts
@@ -0,0 +1,75 @@
+import type { SessionPreviewTab } from './sessionState.svelte'
+import { stripBase, TRIGGER_PAGES, type TriggerKind } from './previewRouter'
+
+// Which list pages a completed chat tool can change, as base-stripped paths
+// (e.g. `/schedules`). This allowlist is the single source of truth for "does
+// this tool change a list page a preview tab might show". A new mutating tool
+// that surfaces on one of these pages must be added here or that tab silently
+// goes stale — match by exact tool name, never a name regex, which mis-classifies
+// purely-local tools (e.g. `update_user_instructions`) as page mutations.
+//
+// Item-editor writes (write_script / write_flow / init_app / write_app_*) are
+// deliberately absent: every editable item is a live in-process editor that
+// self-syncs from the store the chat mutates, so its tab needs no reload — and
+// no list page we preview lists open drafts. They fall through to NO_RELOAD.
+// This "live editors self-sync, only list pages reload" invariant is the reason
+// the callers below and in the sessions page reload nothing for item tabs.
+export type ToolReloadEffect = { pages: string[] }
+const NO_RELOAD: ToolReloadEffect = { pages: [] }
+
+export function toolReloadEffect(name: string, args: any): ToolReloadEffect {
+	switch (name) {
+		case 'write_schedule':
+			return { pages: ['/schedules'] }
+		case 'write_trigger':
+			return { pages: triggerPages(args?.kind) }
+		case 'write_resource':
+			return { pages: ['/resources'] }
+		case 'write_variable':
+			return { pages: ['/variables'] }
+		case 'create_folder':
+			return { pages: ['/folders'] }
+		// Generic item tools carry a workspace-item `type`; refresh its list page
+		// when it lives on one (schedule/resource/variable/trigger). script/flow/app
+		// have their own live editor tab and no previewed list page → nothing.
+		case 'delete_workspace_item':
+		case 'discard_local_draft':
+		case 'deploy_workspace_item':
+		case 'rebase_draft':
+			return { pages: pagesForItemType(args?.type, args) }
+		default:
+			return NO_RELOAD
+	}
+}
+
+function pagesForItemType(type: unknown, args: any): string[] {
+	switch (type) {
+		case 'schedule':
+			return ['/schedules']
+		case 'resource':
+			return ['/resources']
+		case 'variable':
+			return ['/variables']
+		case 'trigger':
+			return triggerPages(args?.trigger_kind)
+		default:
+			return []
+	}
+}
+
+function triggerPages(kind: unknown): string[] {
+	const page = TRIGGER_PAGES[kind as TriggerKind]
+	return page ? [page.path] : []
+}
+
+// The open tabs a page-reload should refresh: those whose observed page path is
+// in `pages`. Item-editor and pipeline tab routes are never list pages, so they
+// never match (see the self-sync invariant above). Pure over a tab snapshot so
+// the sessions page can reload by id and this stays unit-testable.
+export function tabsToReload(
+	tabs: SessionPreviewTab[],
+	pages: ReadonlySet<string>
+): SessionPreviewTab[] {
+	if (pages.size === 0) return []
+	return tabs.filter((t) => pages.has(stripBase(t.loc || t.url)))
+}
diff --git a/frontend/src/lib/components/sessions/previewRouter.test.ts b/frontend/src/lib/components/sessions/previewRouter.test.ts
index a9a36ed462..0c8ee64d89 100644
--- a/frontend/src/lib/components/sessions/previewRouter.test.ts
+++ b/frontend/src/lib/components/sessions/previewRouter.test.ts
@@ -1,6 +1,5 @@
 import { describe, it, expect } from 'vitest'
 import { parsePreviewItemRoute, resolvePreviewTab } from './previewRouter'
-import type { SessionTarget } from './sessionState.svelte'
 
 describe('parsePreviewItemRoute', () => {
 	it('maps edit/get routes to item kinds', () => {
@@ -34,33 +33,28 @@ describe('parsePreviewItemRoute', () => {
 })
 
 describe('resolvePreviewTab', () => {
-	const scriptTarget: SessionTarget = { kind: 'script', path: 'f/foo/bar' }
-
 	it('routes a static page to the iframe fallback', () => {
-		expect(resolvePreviewTab('/runs', scriptTarget)).toEqual({ kind: 'iframe' })
+		expect(resolvePreviewTab('/runs')).toEqual({ kind: 'iframe' })
 	})
 
-	it('routes the matching target item to a live editor', () => {
-		expect(resolvePreviewTab('/scripts/edit/f/foo/bar', scriptTarget)).toEqual({
+	it('routes any script item to a live editor', () => {
+		expect(resolvePreviewTab('/scripts/edit/f/foo/bar')).toEqual({
 			kind: 'editor',
 			editorKind: 'script',
 			path: 'f/foo/bar'
 		})
 	})
 
-	it('routes a same-kind but different item to the iframe (one editor per session)', () => {
-		expect(resolvePreviewTab('/scripts/edit/f/other/script', scriptTarget)).toEqual({
-			kind: 'iframe'
+	it('routes any flow item to a live editor', () => {
+		expect(resolvePreviewTab('/flows/edit/f/foo/bar')).toEqual({
+			kind: 'editor',
+			editorKind: 'flow',
+			path: 'f/foo/bar'
 		})
 	})
 
-	it('routes a different-kind item to the iframe even when it matches no target', () => {
-		expect(resolvePreviewTab('/flows/edit/f/foo/bar', scriptTarget)).toEqual({ kind: 'iframe' })
-	})
-
-	it('maps a raw-app target to the raw_app editor kind', () => {
-		const target: SessionTarget = { kind: 'raw_app', path: 'f/a/b' }
-		expect(resolvePreviewTab('/apps_raw/edit/f/a/b', target)).toEqual({
+	it('maps a raw app to the raw_app editor kind', () => {
+		expect(resolvePreviewTab('/apps_raw/edit/f/a/b')).toEqual({
 			kind: 'editor',
 			editorKind: 'raw_app',
 			path: 'f/a/b'
@@ -68,11 +62,18 @@ describe('resolvePreviewTab', () => {
 	})
 
 	it('never routes a regular drag-and-drop app to an editor (no wrapper exists)', () => {
-		const target = { kind: 'raw_app', path: 'f/a/b' } as SessionTarget
-		expect(resolvePreviewTab('/apps/edit/f/a/b', target)).toEqual({ kind: 'iframe' })
+		expect(resolvePreviewTab('/apps/edit/f/a/b')).toEqual({ kind: 'iframe' })
 	})
 
-	it('falls back to the iframe when the session has no target', () => {
-		expect(resolvePreviewTab('/scripts/edit/f/foo/bar', undefined)).toEqual({ kind: 'iframe' })
+	it('routes a pipeline folder to the pipeline editor kind', () => {
+		expect(resolvePreviewTab('/pipeline/my_folder')).toEqual({
+			kind: 'editor',
+			editorKind: 'pipeline',
+			path: 'my_folder'
+		})
+	})
+
+	it('routes the bare pipeline list page to the iframe fallback', () => {
+		expect(resolvePreviewTab('/pipeline')).toEqual({ kind: 'iframe' })
 	})
 })
diff --git a/frontend/src/lib/components/sessions/previewRouter.ts b/frontend/src/lib/components/sessions/previewRouter.ts
index 37e8c9c595..8fcd038f79 100644
--- a/frontend/src/lib/components/sessions/previewRouter.ts
+++ b/frontend/src/lib/components/sessions/previewRouter.ts
@@ -13,7 +13,6 @@ import {
 } from 'lucide-svelte'
 import type { DrillIcon } from '$lib/components/drillPicker'
 import type { WorkspaceItem, WorkspaceItemKind } from '$lib/components/workspacePicker'
-import type { SessionTarget } from './sessionState.svelte'
 import type { SessionTargetKind } from './sessionRuntime.svelte'
 
 /** What the preview breadcrumb picker can route to: a static workspace page
@@ -104,6 +103,8 @@ export function previewLocationLabel(url: string): string {
 	if (trigger) return trigger
 	const run = stripBase(url).match(/^\/run\/([^/?#]+)/)
 	if (run) return `Run ${decodeURIComponent(run[1]).slice(0, 8)}`
+	const pipelineFolder = parsePipelineRoute(url)
+	if (pipelineFolder) return pipelineFolder
 	const parsed = parsePreviewItemRoute(url)
 	if (parsed) return parsed.itemPath.split('/').pop() ?? parsed.itemPath
 	return stripBase(url)
@@ -125,16 +126,27 @@ export function parsePreviewItemRoute(fullPath: string): PreviewItemRoute | null
 	return { kind: 'app', raw_app: false, itemPath }
 }
 
-// How a preview tab should render: as an in-process live editor (sharing the
-// session runtime's store) or as an iframe fallback. Only the three kinds with
-// existing editor wrappers — and only the tab matching the session's target —
-// resolve to 'editor'; everything else (static pages, regular drag-and-drop
-// apps, any other item) stays an iframe.
+// A `/pipeline/<folder>` route is the data-pipeline graph editor for that folder
+// (the folder is a single path segment, not a workspace item path). The bare
+// `/pipeline` list page is not an editor. Returns the folder name, or null.
+export function parsePipelineRoute(fullPath: string): string | null {
+	const m = stripBase(fullPath).match(/^\/pipeline\/([^/?#]+)/)
+	return m ? decodeURIComponent(m[1]) : null
+}
+
+// How a preview tab should render: as an in-process live editor or an iframe
+// fallback. Any editable item of a wrappable kind (script, flow, raw app) mounts
+// its per-(kind,path) cell editor; a `/pipeline/<folder>` route mounts the
+// data-pipeline graph editor (single, shared runtime.pipelineEditorState — `path`
+// is the folder); everything else (static pages, regular drag-and-drop apps, any
+// other route) stays an iframe.
 export type PreviewSlot =
-	| { kind: 'editor'; editorKind: SessionTargetKind; path: string }
+	| { kind: 'editor'; editorKind: SessionTargetKind | 'pipeline'; path: string }
 	| { kind: 'iframe' }
 
-export function resolvePreviewTab(url: string, target: SessionTarget | undefined): PreviewSlot {
+export function resolvePreviewTab(url: string): PreviewSlot {
+	const pipelineFolder = parsePipelineRoute(url)
+	if (pipelineFolder) return { kind: 'editor', editorKind: 'pipeline', path: pipelineFolder }
 	const route = parsePreviewItemRoute(url)
 	if (!route) return { kind: 'iframe' }
 	const editorKind: SessionTargetKind | undefined =
@@ -146,11 +158,5 @@ export function resolvePreviewTab(url: string, target: SessionTarget | undefined
 					? 'raw_app'
 					: undefined
 	if (!editorKind) return { kind: 'iframe' }
-	// SessionRuntime holds one load slot per kind, so only the tab pointing at the
-	// session's own target claims it as a live editor; any other item previews as
-	// an iframe (the "one live editor per session" rule).
-	if (!target || target.kind !== editorKind || target.path !== route.itemPath) {
-		return { kind: 'iframe' }
-	}
 	return { kind: 'editor', editorKind, path: route.itemPath }
 }
diff --git a/frontend/src/lib/components/sessions/sessionDraftCodecs.test.ts b/frontend/src/lib/components/sessions/sessionDraftCodecs.test.ts
index fd20c4e2dc..dc2d8cd132 100644
--- a/frontend/src/lib/components/sessions/sessionDraftCodecs.test.ts
+++ b/frontend/src/lib/components/sessions/sessionDraftCodecs.test.ts
@@ -6,12 +6,11 @@ import { describe, it, expect, vi } from 'vitest'
 vi.mock('$lib/components/flows/flowState', () => ({ initFlowState: () => Promise.resolve() }))
 
 import { makeScriptCodec } from './sessionDraftCodecs'
-import type { SessionRuntime } from './sessionRuntime.svelte'
 import type { NewScript } from '$lib/gen'
 
-// Minimal runtime stub: the script codec only touches `runtime.scriptStore.val`.
-function runtimeWith(script: Partial<NewScript> & { path: string }): SessionRuntime {
-	return { scriptStore: { val: script as NewScript } } as unknown as SessionRuntime
+// The script codec closes over one cell's store — a plain `{ val }` object.
+function storeWith(script: Partial<NewScript> & { path: string }): { val: NewScript } {
+	return { val: script as NewScript }
 }
 
 const STORAGE = 'u/admin/draft_abc'
@@ -19,7 +18,7 @@ const STORAGE = 'u/admin/draft_abc'
 describe('makeScriptCodec — draft_path (path rename)', () => {
 	it('writes draft_path when the typed path differs from the storage key', () => {
 		const codec = makeScriptCodec(
-			runtimeWith({ path: 'u/admin/friendly', content: 'c', summary: 's' }),
+			storeWith({ path: 'u/admin/friendly', content: 'c', summary: 's' }),
 			() => STORAGE
 		)
 		const draft = codec.storeToDraft(undefined) as (NewScript & { draft_path?: string }) | undefined
@@ -28,7 +27,7 @@ describe('makeScriptCodec — draft_path (path rename)', () => {
 
 	it('drops draft_path when the typed path equals the storage key', () => {
 		const codec = makeScriptCodec(
-			runtimeWith({ path: STORAGE, content: 'c', summary: 's' }),
+			storeWith({ path: STORAGE, content: 'c', summary: 's' }),
 			() => STORAGE
 		)
 		const draft = codec.storeToDraft(undefined) as (NewScript & { draft_path?: string }) | undefined
@@ -36,9 +35,9 @@ describe('makeScriptCodec — draft_path (path rename)', () => {
 	})
 
 	it('signature changes on a rename, so the outbound sync persists it', () => {
-		const before = makeScriptCodec(runtimeWith({ path: STORAGE, content: 'c' }), () => STORAGE)
+		const before = makeScriptCodec(storeWith({ path: STORAGE, content: 'c' }), () => STORAGE)
 		const after = makeScriptCodec(
-			runtimeWith({ path: 'u/admin/renamed', content: 'c' }),
+			storeWith({ path: 'u/admin/renamed', content: 'c' }),
 			() => STORAGE
 		)
 		expect(before.sig(before.storeToDraft(undefined)!)).not.toBe(
diff --git a/frontend/src/lib/components/sessions/sessionDraftCodecs.ts b/frontend/src/lib/components/sessions/sessionDraftCodecs.ts
index 9222438534..2f531f2406 100644
--- a/frontend/src/lib/components/sessions/sessionDraftCodecs.ts
+++ b/frontend/src/lib/components/sessions/sessionDraftCodecs.ts
@@ -2,35 +2,41 @@ import type { Flow, NewScript } from '$lib/gen'
 import { initFlowState } from '$lib/components/flows/flowState'
 import { flowDraftSig } from './flowDraftSig'
 import { applyDraftToRuntimeRawApp, runtimeRawAppToDraft, type RawAppDraft } from './appDraftCodec'
-import type { SessionRuntime } from './sessionRuntime.svelte'
+import type { RawAppRuntimeValue } from './sessionRuntime.svelte'
+import type { StateStore } from '$lib/utils'
 import type { DraftSyncCodec } from './useUserDraftSync.svelte'
 
 // Outbound debounce, uniform across kinds (script was previously immediate;
 // unified to 150ms so a typing burst coalesces into one persist like flow/raw_app).
 const DEBOUNCE_MS = 150
 
-export function makeFlowCodec(runtime: SessionRuntime): DraftSyncCodec<Flow> {
+// Each codec closes over one editor cell's store, so two live editors of the
+// same kind sync to their own drafts without crossing.
+export function makeFlowCodec(
+	store: StateStore<Flow>,
+	stateStore: { val: Record<string, any> }
+): DraftSyncCodec<Flow> {
 	return {
 		itemKind: 'flow',
 		sig: flowDraftSig,
 		debounceMs: DEBOUNCE_MS,
 		applyDraftToStore(incoming) {
-			const current = runtime.flowStore.val
+			const current = store.val
 			if (!current) return
-			runtime.flowStore.val = {
+			store.val = {
 				...current,
 				value: incoming.value,
 				schema: incoming.schema ?? current.schema,
 				summary: incoming.summary ?? current.summary,
 				description: incoming.description ?? current.description
 			}
-			// flowStateStore is keyed by module_id; after an AI write the set of
+			// stateStore is keyed by module_id; after an AI write the set of
 			// module ids may differ, so rebuild the UI state. This wipes per-module
 			// test args / preview output — a known v1 trade-off.
-			void initFlowState(runtime.flowStore.val, runtime.flowStateStore)
+			void initFlowState(store.val, stateStore)
 		},
 		storeToDraft() {
-			return runtime.flowStore.val
+			return store.val
 		}
 	}
 }
@@ -40,7 +46,7 @@ export function makeFlowCodec(runtime: SessionRuntime): DraftSyncCodec<Flow> {
 type ScriptDraft = NewScript & { draft_path?: string }
 
 export function makeScriptCodec(
-	runtime: SessionRuntime,
+	store: { val: NewScript | undefined },
 	// The draft's storage key (the URL path). A never-deployed script is parked
 	// here at `…/draft_<uuid>` while the user's typed name lives in `script.path`.
 	storagePath: () => string
@@ -63,7 +69,7 @@ export function makeScriptCodec(
 			}),
 		debounceMs: DEBOUNCE_MS,
 		applyDraftToStore(incoming) {
-			const script = runtime.scriptStore.val
+			const script = store.val
 			if (!script) return
 			if (typeof incoming.content !== 'string') return
 			script.content = incoming.content
@@ -71,7 +77,7 @@ export function makeScriptCodec(
 			if (incoming.summary !== undefined) script.summary = incoming.summary
 		},
 		storeToDraft(current) {
-			const script = runtime.scriptStore.val
+			const script = store.val
 			if (!script) return undefined
 			// Merge over the existing entry so fields the preview doesn't edit
 			// (set by the chat) survive a content-only save.
@@ -89,18 +95,20 @@ export function makeScriptCodec(
 	}
 }
 
-export function makeRawAppCodec(runtime: SessionRuntime): DraftSyncCodec<RawAppDraft> {
+export function makeRawAppCodec(store: {
+	val: RawAppRuntimeValue | undefined
+}): DraftSyncCodec<RawAppDraft> {
 	return {
 		itemKind: 'raw_app',
 		sig: (d) => JSON.stringify(d),
 		debounceMs: DEBOUNCE_MS,
 		applyDraftToStore(incoming) {
-			const current = runtime.rawApp.val
+			const current = store.val
 			if (!current) return
-			runtime.rawApp.val = applyDraftToRuntimeRawApp(current, incoming)
+			store.val = applyDraftToRuntimeRawApp(current, incoming)
 		},
 		storeToDraft() {
-			const raw = runtime.rawApp.val
+			const raw = store.val
 			if (!raw) return undefined
 			return runtimeRawAppToDraft(raw)
 		}
diff --git a/frontend/src/lib/components/sessions/sessionPreviewTabs.svelte.ts b/frontend/src/lib/components/sessions/sessionPreviewTabs.svelte.ts
index dbb4149472..be25a3a75d 100644
--- a/frontend/src/lib/components/sessions/sessionPreviewTabs.svelte.ts
+++ b/frontend/src/lib/components/sessions/sessionPreviewTabs.svelte.ts
@@ -3,21 +3,21 @@ import { randomUUID } from '$lib/utils/uuid'
 import { editPathFor, type WorkspaceItem } from '$lib/components/workspacePicker'
 import {
 	matchPreviewPage,
+	parsePipelineRoute,
 	parsePreviewItemRoute,
 	previewLocationLabel,
 	resolvePreviewTab,
 	stripBase,
 	type PreviewTarget
 } from './previewRouter'
-import { sessionTargetHref } from './sessionMode.svelte'
 import type { SessionPreviewTab, SessionTarget } from './sessionState.svelte'
 
 // The single live owner of a session's preview tabs. Runs behind a small
 // interface both the sessions page (renderer) and the `open_preview` tool cross,
 // so there is exactly one live copy of the tab model instead of three drifting
-// ones synced by effects. Persistence and the session-record `target` write are
-// injected as an adapter, so the class is pure runes with no sessionState / IDB
-// coupling (mirrors PipelineEditorState). Held on SessionRuntime.previewTabs.
+// ones synced by effects. Persistence (and cell pruning) are injected as an
+// adapter, so the class is pure runes with no sessionState / IDB coupling
+// (mirrors PipelineEditorState). Held on SessionRuntime.previewTabs.
 
 export type PreviewTabsSnapshot = {
 	tabs: SessionPreviewTab[]
@@ -29,9 +29,17 @@ export type PreviewTabsAdapter = {
 	// Write-behind the full tab model onto the durable backing (debounced by the
 	// owner). Fire-and-forget.
 	persist: (snapshot: PreviewTabsSnapshot) => void
-	// Point the session's live editor at `target`. Called atomically with the tab
-	// open/navigate that shows the item, so tab and target can never drift apart.
-	setTarget: (target: SessionTarget) => void
+	// Fired synchronously on every tab-set change, so the runtime can drop editor
+	// cells no open tab references anymore (a closed / navigated-away item).
+	onTabsChanged?: () => void
+}
+
+// True when a tab's URL is the live editor for a specific editable item. Every
+// editable route resolves to an editor, so this doubles as the "same item" dedupe
+// test in open()/navigate().
+function isEditorTabFor(url: string, target: SessionTarget): boolean {
+	const slot = resolvePreviewTab(url)
+	return slot.kind === 'editor' && slot.editorKind === target.kind && slot.path === target.path
 }
 
 // URL a tab should load for a destination: a page's href, or an item's edit route.
@@ -56,8 +64,8 @@ export function canonicalizeObservedLoc(loc: string): string {
 }
 
 // The editor target a destination maps to, or undefined when it isn't an item we
-// host live (static pages, legacy drag-and-drop apps). Drives the "set the
-// session target iff the destination is an editable item" rule.
+// host live (static pages, legacy drag-and-drop apps). Drives the open()/navigate()
+// dedupe — one editor tab per (kind, path).
 function editorTargetFor(target: PreviewTarget): SessionTarget | undefined {
 	if (target.type !== 'item') return undefined
 	const item = target.item
@@ -68,13 +76,16 @@ function editorTargetFor(target: PreviewTarget): SessionTarget | undefined {
 }
 
 // Adapt a session editor target (`open_preview` tool arg) to a preview
-// destination. Pipeline targets have no full-page route, so they can't be
-// previewed as a tab (returns undefined).
+// destination. A pipeline target's `path` is a folder name, not a workspace
+// item — it maps to the `/pipeline/<folder>` route, which resolvePreviewTab
+// mounts as the in-process graph editor.
 export function previewTargetForSessionTarget(
 	kind: SessionTarget['kind'],
 	path: string
 ): PreviewTarget | undefined {
-	if (kind === 'pipeline') return undefined
+	if (kind === 'pipeline') {
+		return { type: 'page', href: `${base}/pipeline/${encodeURIComponent(path)}`, label: path }
+	}
 	const item: WorkspaceItem =
 		kind === 'raw_app'
 			? { kind: 'app', raw_app: true, path, summary: '' }
@@ -82,14 +93,12 @@ export function previewTargetForSessionTarget(
 	return { type: 'item', item }
 }
 
-// Build the initial tab model for a session: its saved tabs, else a single tab
-// on its editor target, else empty. Default collapse: collapsed only for a
-// session with nothing to preview.
+// Build the initial tab model for a session: its saved tabs, else empty. Default
+// collapse: collapsed only for a session with nothing to preview.
 export function hydratePreviewTabs(session: {
 	previewTabs?: SessionPreviewTab[]
 	activePreviewTabId?: string
 	previewCollapsed?: boolean
-	target?: SessionTarget
 }): PreviewTabsSnapshot {
 	// Saved tabs come straight from IndexedDB — drop malformed records (missing
 	// id/url) and duplicate ids, which would break the page's keyed {#each}.
@@ -107,14 +116,6 @@ export function hydratePreviewTabs(session: {
 		const activeId = wantActive && tabs.some((t) => t.id === wantActive) ? wantActive : tabs[0].id
 		return { tabs, activeId, collapsed: session.previewCollapsed ?? false }
 	}
-	const seedUrl = sessionTargetHref(session.target)
-	if (seedUrl) {
-		return {
-			tabs: [{ id: 'session', url: seedUrl, loc: seedUrl }],
-			activeId: 'session',
-			collapsed: session.previewCollapsed ?? false
-		}
-	}
 	return { tabs: [], activeId: '', collapsed: session.previewCollapsed ?? true }
 }
 
@@ -158,21 +159,16 @@ export class SessionPreviewTabs {
 	}
 
 	// Open — or focus, if already shown — a tab for a destination, and reveal the
-	// panel. An editable item is made the session's live editor (setTarget) and
-	// deduped against the tab already hosting it; anything else dedupes on the
-	// tab's observed location.
+	// panel. An editable item dedupes against the tab already hosting that same
+	// (kind, path); anything else dedupes on the tab's observed location.
 	open(target: PreviewTarget): { status: 'opened' | 'focused' } {
 		const editorTarget = editorTargetFor(target)
-		if (editorTarget) this.#adapter.setTarget(editorTarget)
 		// A fresh session starts collapsed, so without this the tab opens behind a
 		// collapsed panel and the user sees nothing change.
 		this.#collapsed = false
 		if (editorTarget) {
-			// resolvePreviewTab(url, target) is 'editor' exactly for the tab showing
-			// `target`'s item, so it doubles as the dedupe test.
-			const existing = this.#tabs.find(
-				(t) => resolvePreviewTab(t.url, editorTarget).kind === 'editor'
-			)
+			// One editor tab per item: focus the tab already hosting this exact item.
+			const existing = this.#tabs.find((t) => isEditorTabFor(t.url, editorTarget))
 			if (existing) {
 				this.#activeId = existing.id
 				this.#flush()
@@ -180,6 +176,23 @@ export class SessionPreviewTabs {
 			}
 		}
 		const url = targetUrl(target)
+		// Pipeline previews all share one runtime.pipelineEditorState, so keep at
+		// most one pipeline tab: re-point the existing one to the requested folder
+		// rather than opening a second pipeline editor that would fight over the
+		// shared state (`focused` when it already showed this folder, else `opened`
+		// since the view now shows a different pipeline).
+		const pipelineFolder = parsePipelineRoute(url)
+		if (pipelineFolder) {
+			const existing = this.#tabs.find((t) => parsePipelineRoute(t.url) !== null)
+			if (existing) {
+				const same = existing.url === url
+				existing.url = url
+				existing.loc = url
+				this.#activeId = existing.id
+				this.#flush()
+				return { status: same ? 'focused' : 'opened' }
+			}
+		}
 		// Focus the tab currently *showing* this destination instead of opening a
 		// duplicate. Matched on the observed `loc`, not `url`: a tab that was
 		// opened here but navigated away no longer counts as showing it.
@@ -197,21 +210,16 @@ export class SessionPreviewTabs {
 	}
 
 	// Re-point the active tab at a destination (breadcrumb pick / in-editor link /
-	// iframe-posted editor navigation). Same target rule as open: an editable item
-	// becomes the session's live editor.
+	// iframe-posted editor navigation).
 	navigate(target: PreviewTarget): void {
 		const t = this.#tabs.find((x) => x.id === this.#activeId)
 		if (!t) return
 		const editorTarget = editorTargetFor(target)
 		if (editorTarget) {
-			this.#adapter.setTarget(editorTarget)
-			// Same dedupe as open(): if another tab already hosts `target` as the
-			// live editor, focus it instead of re-pointing this one — two tabs
-			// resolving 'editor' for one target would mount two editor instances
-			// on the same runtime slot.
-			const existing = this.#tabs.find(
-				(x) => resolvePreviewTab(x.url, editorTarget).kind === 'editor'
-			)
+			// Same dedupe as open(): if another tab already hosts this exact item,
+			// focus it instead of re-pointing this one — two tabs for one item would
+			// mount two editors racing the same (kind, path) cell.
+			const existing = this.#tabs.find((x) => isEditorTabFor(x.url, editorTarget))
 			if (existing && existing.id !== t.id) {
 				this.#activeId = existing.id
 				this.#flush()
@@ -219,6 +227,21 @@ export class SessionPreviewTabs {
 			}
 		}
 		const url = targetUrl(target)
+		// Keep at most one pipeline tab (all share runtime.pipelineEditorState): if a
+		// *different* tab already hosts a pipeline, retarget and focus it rather than
+		// turning the active tab into a second pipeline editor racing the shared
+		// state. Same invariant as open(); a no-op when the active tab is that tab.
+		const pipelineFolder = parsePipelineRoute(url)
+		if (pipelineFolder) {
+			const existing = this.#tabs.find((x) => parsePipelineRoute(x.url) !== null)
+			if (existing && existing.id !== t.id) {
+				existing.url = url
+				existing.loc = url
+				this.#activeId = existing.id
+				this.#flush()
+				return
+			}
+		}
 		t.url = url
 		t.loc = url
 		this.#flush()
@@ -298,6 +321,9 @@ export class SessionPreviewTabs {
 	}
 
 	#flush(): void {
+		// Prune cells promptly (cheap, synchronous) even though the durable persist
+		// stays debounced — a closed tab's editor cell should be reclaimable now.
+		this.#adapter.onTabsChanged?.()
 		clearTimeout(this.#flushHandle)
 		this.#flushHandle = setTimeout(() => {
 			this.#flushHandle = undefined
@@ -335,25 +361,23 @@ export function selectPreviewTabsToClose(
 }
 
 // Human-readable summary of a session's open preview tabs, for the
-// `get_preview_status` AI tool. Pure over the owner's model + the session target
-// so the owner needs no target-read dependency. The "no session" case is the
-// caller's (the tool handler has the session context).
-export function describePreview(
-	tabs: SessionPreviewTab[],
-	activeId: string,
-	target: SessionTarget | undefined
-): string {
+// `get_preview_status` AI tool. Pure over the owner's model. The "no session"
+// case is the caller's (the tool handler has the session context).
+export function describePreview(tabs: SessionPreviewTab[], activeId: string): string {
 	if (tabs.length === 0) return 'No preview tabs are open in the side panel.'
 	const lines = tabs.map((t) => {
 		const where = t.loc || t.url
 		const page = matchPreviewPage(where)
+		const pipelineFolder = parsePipelineRoute(where)
 		const route = parsePreviewItemRoute(where)
 		const label = page
 			? `page "${page.label}"`
-			: route
-				? `${route.raw_app ? 'raw_app' : route.kind} "${route.itemPath}"`
-				: stripBase(where)
-		const live = resolvePreviewTab(t.url, target).kind === 'editor' ? ', live editor' : ''
+			: pipelineFolder
+				? `pipeline "${pipelineFolder}"`
+				: route
+					? `${route.raw_app ? 'raw_app' : route.kind} "${route.itemPath}"`
+					: stripBase(where)
+		const live = resolvePreviewTab(t.url).kind === 'editor' ? ', live editor' : ''
 		const active = t.id === activeId ? ', active' : ''
 		return `- ${label}${live}${active}`
 	})
diff --git a/frontend/src/lib/components/sessions/sessionPreviewTabs.test.ts b/frontend/src/lib/components/sessions/sessionPreviewTabs.test.ts
index 08f139499e..00e3f6cc90 100644
--- a/frontend/src/lib/components/sessions/sessionPreviewTabs.test.ts
+++ b/frontend/src/lib/components/sessions/sessionPreviewTabs.test.ts
@@ -9,17 +9,16 @@ import {
 	type PreviewTabsSnapshot
 } from './sessionPreviewTabs.svelte'
 import type { PreviewTarget } from './previewRouter'
-import type { SessionPreviewTab, SessionTarget } from './sessionState.svelte'
+import type { SessionPreviewTab } from './sessionState.svelte'
+import { base } from '$lib/base'
 
-// In-memory adapter spy: records persisted snapshots + target writes, no IDB.
+// In-memory adapter spy: records persisted snapshots, no IDB.
 function makeAdapter() {
 	const persisted: PreviewTabsSnapshot[] = []
-	const targets: SessionTarget[] = []
 	const adapter: PreviewTabsAdapter = {
-		persist: (snap) => persisted.push(snap),
-		setTarget: (t) => targets.push(t)
+		persist: (snap) => persisted.push(snap)
 	}
-	return { adapter, persisted, targets }
+	return { adapter, persisted }
 }
 
 function owner(initial: Partial<PreviewTabsSnapshot> = {}, adapter?: PreviewTabsAdapter) {
@@ -48,6 +47,12 @@ const dndAppTarget: PreviewTarget = {
 	item: { kind: 'app', path: 'u/me/legacy', summary: '' }
 }
 const pageTarget: PreviewTarget = { type: 'page', href: '/runs', label: 'Runs' }
+const pipelineTarget: PreviewTarget = { type: 'page', href: `${base}/pipeline/crm`, label: 'crm' }
+const pipelineTarget2: PreviewTarget = {
+	type: 'page',
+	href: `${base}/pipeline/sales`,
+	label: 'sales'
+}
 
 beforeEach(() => {
 	vi.useFakeTimers()
@@ -76,15 +81,6 @@ describe('hydratePreviewTabs', () => {
 		expect(snap.activeId).toBe('a')
 	})
 
-	it('seeds a single tab on the editor target when there are no saved tabs', () => {
-		const snap = hydratePreviewTabs({ target: { kind: 'script', path: 'u/me/foo' } })
-		expect(snap.tabs).toEqual([
-			{ id: 'session', url: '/scripts/edit/u/me/foo', loc: '/scripts/edit/u/me/foo' }
-		])
-		expect(snap.activeId).toBe('session')
-		expect(snap.collapsed).toBe(false)
-	})
-
 	it('is empty and collapsed for a session with nothing to preview', () => {
 		const snap = hydratePreviewTabs({})
 		expect(snap.tabs).toEqual([])
@@ -93,10 +89,7 @@ describe('hydratePreviewTabs', () => {
 	})
 
 	it('honours an explicit previewCollapsed override', () => {
-		expect(
-			hydratePreviewTabs({ previewCollapsed: true, target: { kind: 'script', path: 'p' } })
-				.collapsed
-		).toBe(true)
+		expect(hydratePreviewTabs({ previewCollapsed: true }).collapsed).toBe(true)
 		expect(hydratePreviewTabs({ previewCollapsed: false }).collapsed).toBe(false)
 	})
 
@@ -115,13 +108,12 @@ describe('hydratePreviewTabs', () => {
 		expect(snap.activeId).toBe('a')
 	})
 
-	it('falls back to the target seed when every saved tab is malformed', () => {
+	it('is empty when every saved tab is malformed', () => {
 		const snap = hydratePreviewTabs({
-			previewTabs: [{ id: '', url: '', loc: '' }],
-			target: { kind: 'script', path: 'u/me/foo' }
+			previewTabs: [{ id: '', url: '', loc: '' }]
 		})
-		expect(snap.tabs).toHaveLength(1)
-		expect(snap.activeId).toBe('session')
+		expect(snap.tabs).toEqual([])
+		expect(snap.activeId).toBe('')
 	})
 })
 
@@ -142,22 +134,24 @@ describe('previewTargetForSessionTarget', () => {
 			item: { kind: 'flow', path: 'p', summary: '' }
 		})
 	})
-	it('returns undefined for pipeline (no full-page route)', () => {
-		expect(previewTargetForSessionTarget('pipeline', 'p')).toBeUndefined()
+	it('maps pipeline to its folder route page target', () => {
+		expect(previewTargetForSessionTarget('pipeline', 'my_folder')).toEqual({
+			type: 'page',
+			href: `${base}/pipeline/my_folder`,
+			label: 'my_folder'
+		})
 	})
 })
 
 describe('SessionPreviewTabs.open', () => {
-	it('opens an editor item, points the target at it, activates it, and reveals the panel', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({ collapsed: true }, adapter)
+	it('opens an editor item, activates it, and reveals the panel', () => {
+		const o = owner({ collapsed: true })
 		const res = o.open(scriptTarget)
 		expect(res.status).toBe('opened')
 		expect(o.tabs).toHaveLength(1)
 		expect(o.tabs[0].url).toBe('/scripts/edit/u/me/foo')
 		expect(o.activeId).toBe(o.tabs[0].id)
 		expect(o.collapsed).toBe(false)
-		expect(targets).toEqual([{ kind: 'script', path: 'u/me/foo' }])
 	})
 
 	it('focuses the existing tab instead of duplicating when the item is already shown', () => {
@@ -171,27 +165,23 @@ describe('SessionPreviewTabs.open', () => {
 		expect(o.activeId).toBe(firstId)
 	})
 
-	it('opens a second tab and repoints the live editor for a different item', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({}, adapter)
+	it('opens a second tab for a different editor item', () => {
+		const o = owner()
 		o.open(scriptTarget)
 		const res = o.open(flowTarget)
 		expect(res.status).toBe('opened')
 		expect(o.tabs).toHaveLength(2)
-		expect(targets.at(-1)).toEqual({ kind: 'flow', path: 'u/me/bar' })
+		expect(o.tabs.at(-1)!.url).toBe('/flows/edit/u/me/bar')
 	})
 
 	it('opens a raw app via its apps_raw route', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({}, adapter)
+		const o = owner()
 		o.open(rawAppTarget)
 		expect(o.tabs[0].url).toBe('/apps_raw/edit/u/me/app')
-		expect(targets).toEqual([{ kind: 'raw_app', path: 'u/me/app' }])
 	})
 
-	it('focuses the tab already showing a page instead of duplicating, and never sets a target', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({}, adapter)
+	it('focuses the tab already showing a page instead of duplicating', () => {
+		const o = owner()
 		o.open(pageTarget)
 		const firstId = o.activeId
 		o.open(scriptTarget)
@@ -199,7 +189,6 @@ describe('SessionPreviewTabs.open', () => {
 		expect(res.status).toBe('focused')
 		expect(o.tabs).toHaveLength(2)
 		expect(o.activeId).toBe(firstId)
-		expect(targets).toEqual([{ kind: 'script', path: 'u/me/foo' }])
 	})
 
 	it('opens a fresh page tab when the original navigated away', () => {
@@ -221,19 +210,16 @@ describe('SessionPreviewTabs.open', () => {
 		expect(o.tabs).toHaveLength(1)
 	})
 
-	it('does not set a target for a legacy drag-and-drop app', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({}, adapter)
+	it('opens a legacy drag-and-drop app as an iframe route', () => {
+		const o = owner()
 		o.open(dndAppTarget)
-		expect(targets).toEqual([])
 		expect(o.tabs[0].url).toBe('/apps/edit/u/me/legacy')
 	})
 })
 
 describe('SessionPreviewTabs.navigate', () => {
-	it('retargets the active tab and sets the target for an editor item', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({}, adapter)
+	it('retargets the active tab to an editor item', () => {
+		const o = owner()
 		o.open(pageTarget)
 		const tabId = o.activeId
 		o.navigate(flowTarget)
@@ -241,25 +227,19 @@ describe('SessionPreviewTabs.navigate', () => {
 		expect(o.activeId).toBe(tabId)
 		expect(o.tabs[0].url).toBe('/flows/edit/u/me/bar')
 		expect(o.tabs[0].loc).toBe('/flows/edit/u/me/bar')
-		expect(targets).toEqual([{ kind: 'flow', path: 'u/me/bar' }])
 	})
 
 	it('no-ops with no active tab', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({}, adapter)
+		const o = owner()
 		o.navigate(flowTarget)
 		expect(o.tabs).toHaveLength(0)
-		expect(targets).toEqual([])
 	})
 
-	it('retargets to a page without touching the target', () => {
-		const { adapter, targets } = makeAdapter()
-		const o = owner({}, adapter)
+	it('retargets to a page', () => {
+		const o = owner()
 		o.open(scriptTarget)
-		targets.length = 0
 		o.navigate(pageTarget)
 		expect(o.tabs[0].url).toBe('/runs')
-		expect(targets).toEqual([])
 	})
 
 	it('focuses the tab already hosting the item instead of duplicating the editor', () => {
@@ -275,6 +255,31 @@ describe('SessionPreviewTabs.navigate', () => {
 		// The page tab must keep its own url — only focus moved.
 		expect(o.tabs.find((t) => t.id === pageTabId)?.url).toBe('/runs')
 	})
+
+	it('retargets the one pipeline tab instead of turning the active tab into a second', () => {
+		const o = owner()
+		o.open(pipelineTarget)
+		const pipelineTabId = o.activeId
+		o.open(scriptTarget) // a second, non-pipeline tab is now active
+		const scriptTabId = o.activeId
+		o.navigate(pipelineTarget2)
+		// No second pipeline editor: the existing one is retargeted and focused.
+		expect(o.tabs).toHaveLength(2)
+		expect(o.activeId).toBe(pipelineTabId)
+		expect(o.tabs.find((t) => t.id === pipelineTabId)?.url).toBe(`${base}/pipeline/sales`)
+		// The script tab is untouched.
+		expect(o.tabs.find((t) => t.id === scriptTabId)?.url).toBe('/scripts/edit/u/me/foo')
+	})
+
+	it('retargets the active pipeline tab in place to a new folder', () => {
+		const o = owner()
+		o.open(pipelineTarget)
+		const tabId = o.activeId
+		o.navigate(pipelineTarget2)
+		expect(o.tabs).toHaveLength(1)
+		expect(o.activeId).toBe(tabId)
+		expect(o.tabs[0].url).toBe(`${base}/pipeline/sales`)
+	})
 })
 
 describe('SessionPreviewTabs.select / close / setCollapsed', () => {
@@ -442,23 +447,23 @@ describe('SessionPreviewTabs persistence', () => {
 
 describe('describePreview', () => {
 	it('reports no tabs when there are none', () => {
-		expect(describePreview([], '', undefined)).toContain('No preview tabs')
+		expect(describePreview([], '')).toContain('No preview tabs')
 	})
 
 	it('lists tabs, marks the active one, and flags the live editor', () => {
 		const tabs: SessionPreviewTab[] = [
 			{ id: 'a', url: '/scripts/edit/u/me/foo', loc: '/scripts/edit/u/me/foo' }
 		]
-		const out = describePreview(tabs, 'a', { kind: 'script', path: 'u/me/foo' })
+		const out = describePreview(tabs, 'a')
 		expect(out).toContain('1 preview tab')
 		expect(out).toContain('script "u/me/foo"')
 		expect(out).toContain('live editor')
 		expect(out).toContain('active')
 	})
 
-	it('labels a known page and omits the live-editor flag when the target differs', () => {
+	it('labels a known page and omits the live-editor flag for a non-item page', () => {
 		const tabs: SessionPreviewTab[] = [{ id: 'a', url: '/runs', loc: '/runs' }]
-		const out = describePreview(tabs, 'a', { kind: 'script', path: 'u/me/foo' })
+		const out = describePreview(tabs, 'a')
 		expect(out).toContain('page "Runs"')
 		expect(out).not.toContain('live editor')
 	})
diff --git a/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts b/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts
index 261cc6aedc..f55fbe68ec 100644
--- a/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts
+++ b/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts
@@ -1,4 +1,4 @@
-import { SvelteMap, SvelteSet } from 'svelte/reactivity'
+import { SvelteMap } from 'svelte/reactivity'
 import { get } from 'svelte/store'
 import { base } from '$lib/base'
 import { AIChatManager, AIMode } from '$lib/components/copilot/chat/AIChatManager.svelte'
@@ -39,7 +39,6 @@ import {
 	setSessionChatId,
 	setSessionPreviewCollapsed,
 	setSessionTabs,
-	setSessionTarget,
 	type Session
 } from './sessionState.svelte'
 import {
@@ -49,7 +48,7 @@ import {
 	previewTargetForSessionTarget,
 	selectPreviewTabsToClose
 } from './sessionPreviewTabs.svelte'
-import { matchPreviewPage, previewLocationLabel } from './previewRouter'
+import { matchPreviewPage, parsePreviewItemRoute, previewLocationLabel } from './previewRouter'
 import { UserDraft } from '$lib/userDraft.svelte'
 import { UserDraftDbSyncer } from '$lib/userDraftDbSyncer.svelte'
 import { armRestartOnFirstInteraction } from '$lib/userDraftToast'
@@ -93,6 +92,55 @@ export interface LoadSlot {
 
 export type SessionTargetKind = 'flow' | 'script' | 'raw_app'
 
+// The live runtime value a raw-app editor cell binds. Legacy drag-and-drop apps
+// are intentionally NOT hosted in the session preview (only code-based raw apps).
+export interface RawAppRuntimeValue {
+	files: Record<string, string>
+	runnables: Record<string, any>
+	data: RawAppData
+	policy: any
+	summary: string
+	path: string
+	custom_path?: string
+	draft_path?: string
+}
+// The deployed baseline a raw-app cell diffs against (topbar Diff drawer).
+export interface RawAppSavedValue {
+	value: {
+		files: Record<string, { code: string }>
+		runnables: Record<string, HiddenRunnable>
+	}
+	draft?: any
+	path: string
+	summary: string
+	policy: any
+	draft_only?: boolean
+	/** No deployed counterpart (draft-only); disables the topbar Diff. */
+	no_deployed?: boolean
+	custom_path?: string
+}
+
+// One editor cell per (kind, path) the session loads: the load slot plus the
+// content/baseline stores for that item. Keying by path lets several items of the
+// same kind stay loaded — and mounted as separate live editors — at once. A tab's
+// editor resolves its own cell via the accessors below.
+export interface FlowCell {
+	slot: LoadSlot
+	store: StateStore<Flow>
+	stateStore: { val: Record<string, any> }
+	saved: { val: SavedFlow | undefined }
+}
+export interface ScriptCell {
+	slot: LoadSlot
+	store: { val: NewScript | undefined }
+	saved: { val: SavedScript | undefined }
+}
+export interface RawAppCell {
+	slot: LoadSlot
+	store: { val: RawAppRuntimeValue | undefined }
+	saved: { val: RawAppSavedValue | undefined }
+}
+
 export interface SessionRuntime {
 	readonly sessionId: string
 	readonly manager: AIChatManager
@@ -103,54 +151,18 @@ export interface SessionRuntime {
 	// Pipeline target state — persists across editor hide/show (the pane unmounts
 	// on hide, so this can't be component-local) and across session switches.
 	readonly pipelineEditorState: PipelineEditorState
-	// Kind-agnostic accessor over the per-kind load slots, for consumers (the
-	// editor-target gate) that only need load state and not the typed store.
-	slot(kind: SessionTargetKind): LoadSlot
-	// Flow target state
-	readonly flowStore: StateStore<Flow>
-	readonly flowStateStore: { val: Record<string, any> }
-	readonly savedFlow: { val: SavedFlow | undefined }
+	// Per-(kind, path) editor cells (content/baseline stores + load slot), created
+	// on demand. Each editable preview tab resolves its own cell, so several items
+	// stay live at once.
+	flowCell(path: string): FlowCell
 	loadFlow(workspace: string, path: string, force?: boolean): Promise<void>
-	// Script target state (parallel to flow, populated only for script-targeted sessions)
-	readonly scriptStore: { val: NewScript | undefined }
-	readonly savedScript: { val: SavedScript | undefined }
+	scriptCell(path: string): ScriptCell
 	loadScript(workspace: string, path: string, force?: boolean): Promise<void>
-	// Note: legacy drag-and-drop apps are intentionally NOT hosted in the
-	// session preview pane (only code-based raw apps are), so there's no
-	// app target state here.
-	// Raw App (HTML-based) target state
-	readonly rawApp: {
-		val:
-			| {
-					files: Record<string, string>
-					runnables: Record<string, any>
-					data: RawAppData
-					policy: any
-					summary: string
-					path: string
-					custom_path?: string
-					draft_path?: string
-			  }
-			| undefined
-	}
-	readonly savedRawApp: {
-		val:
-			| {
-					value: {
-						files: Record<string, { code: string }>
-						runnables: Record<string, HiddenRunnable>
-					}
-					draft?: any
-					path: string
-					summary: string
-					policy: any
-					draft_only?: boolean
-					/** No deployed counterpart (draft-only); disables the topbar Diff. */
-					no_deployed?: boolean
-					custom_path?: string
-			  }
-			| undefined
-	}
+	rawAppCell(path: string): RawAppCell
+	// Non-creating peek at an editor cell's settled path (undefined when no cell
+	// exists yet for this (kind, path)), so callers can check load state without
+	// the cell accessors' create-on-miss side effect.
+	loadedEditorPath(kind: SessionTargetKind, path: string): string | undefined
 	loadRawApp(
 		workspace: string,
 		path: string,
@@ -185,6 +197,32 @@ function emptyFlow(): Flow {
 	}
 }
 
+function emptyLoadSlot(): LoadSlot {
+	return { loadedPath: undefined, loadedWorkspace: undefined, loading: false, notFound: false }
+}
+
+// Cell factories — a cell starts in the empty-editor state (empty flow / no
+// script / no app) until its first load populates it.
+function makeFlowCell(): FlowCell {
+	const slot: LoadSlot = $state(emptyLoadSlot())
+	const store: StateStore<Flow> = $state({ val: emptyFlow() })
+	const stateStore: { val: Record<string, any> } = $state({ val: {} })
+	const saved: { val: SavedFlow | undefined } = $state({ val: undefined })
+	return { slot, store, stateStore, saved }
+}
+function makeScriptCell(): ScriptCell {
+	const slot: LoadSlot = $state(emptyLoadSlot())
+	const store: { val: NewScript | undefined } = $state({ val: undefined })
+	const saved: { val: SavedScript | undefined } = $state({ val: undefined })
+	return { slot, store, saved }
+}
+function makeRawAppCell(): RawAppCell {
+	const slot: LoadSlot = $state(emptyLoadSlot())
+	const store: { val: RawAppRuntimeValue | undefined } = $state({ val: undefined })
+	const saved: { val: RawAppSavedValue | undefined } = $state({ val: undefined })
+	return { slot, store, saved }
+}
+
 const GENERATED_SUMMARY_TIMEOUT_MS = 15000
 const GENERATED_SUMMARY_MAX_TRANSCRIPT_CHARS = 4000
 const GENERATED_SUMMARY_MAX_LENGTH = 60
@@ -309,48 +347,65 @@ function createRuntime(session: Session): SessionRuntime {
 	}
 	manager.afterFirstTurnSaved = () => generateAndApplySessionSummary(session.id, manager)
 
-	const flowStore: StateStore<Flow> = $state({ val: emptyFlow() })
-	const flowStateStore: { val: Record<string, any> } = $state({ val: {} })
-	const savedFlow: { val: SavedFlow | undefined } = $state({
-		val: undefined
-	})
-
-	const flowSlot: LoadSlot = $state({
-		loadedPath: undefined,
-		loadedWorkspace: undefined,
-		loading: false,
-		notFound: false
-	})
-
-	const scriptStore: { val: NewScript | undefined } = $state({ val: undefined })
-	const savedScript: { val: SavedScript | undefined } = $state({ val: undefined })
-	const scriptSlot: LoadSlot = $state({
-		loadedPath: undefined,
-		loadedWorkspace: undefined,
-		loading: false,
-		notFound: false
-	})
-
-	const rawApp: { val: SessionRuntime['rawApp']['val'] } = $state({ val: undefined })
-	const savedRawApp: { val: SessionRuntime['savedRawApp']['val'] } = $state({ val: undefined })
-	const rawAppSlot: LoadSlot = $state({
-		loadedPath: undefined,
-		loadedWorkspace: undefined,
-		loading: false,
-		notFound: false
-	})
+	// One cell per (kind, path). Created on demand by the load methods; each holds
+	// cached content (KB–MB), not a mounted editor. Bounded to the items open
+	// preview tabs reference: pruneEditorCells (below) drops the rest when the tab
+	// set changes, so re-pointing one tab through many items can't leak cells.
+	const flowCells = new Map<string, FlowCell>()
+	const scriptCells = new Map<string, ScriptCell>()
+	const rawAppCells = new Map<string, RawAppCell>()
+	function flowCell(path: string): FlowCell {
+		let c = flowCells.get(path)
+		if (!c) flowCells.set(path, (c = makeFlowCell()))
+		return c
+	}
+	function scriptCell(path: string): ScriptCell {
+		let c = scriptCells.get(path)
+		if (!c) scriptCells.set(path, (c = makeScriptCell()))
+		return c
+	}
+	function rawAppCell(path: string): RawAppCell {
+		let c = rawAppCells.get(path)
+		if (!c) rawAppCells.set(path, (c = makeRawAppCell()))
+		return c
+	}
+	function loadedEditorPath(kind: SessionTargetKind, path: string): string | undefined {
+		const cell =
+			kind === 'flow'
+				? flowCells.get(path)
+				: kind === 'script'
+					? scriptCells.get(path)
+					: rawAppCells.get(path)
+		return cell?.slot.loadedPath
+	}
+	// Drop every editor cell no open preview tab still points at. Called on each
+	// tab-set change: a closed or navigated-away item's cell (and its cached
+	// content) is reclaimed. Deduping keeps at most one editor tab per item, so an
+	// item absent from the open tabs has no live editor to strand.
+	function pruneEditorCells(): void {
+		const keep = { flow: new Set<string>(), script: new Set<string>(), raw_app: new Set<string>() }
+		for (const t of previewTabs.tabs) {
+			const route = parsePreviewItemRoute(t.url)
+			if (!route) continue
+			const kind = route.raw_app ? 'raw_app' : route.kind
+			if (kind === 'flow' || kind === 'script' || kind === 'raw_app') keep[kind].add(route.itemPath)
+		}
+		for (const p of [...flowCells.keys()]) if (!keep.flow.has(p)) flowCells.delete(p)
+		for (const p of [...scriptCells.keys()]) if (!keep.script.has(p)) scriptCells.delete(p)
+		for (const p of [...rawAppCells.keys()]) if (!keep.raw_app.has(p)) rawAppCells.delete(p)
+	}
 
 	// Hydrate the preview-tab owner from the session record (the durable backing);
 	// from here on the owner is the single live copy and writes back through the
-	// adapter. setSessionTabs / setSessionPreviewCollapsed / setSessionTarget stay
-	// the low-level record writers (a transient session's writes land in the
-	// localStorage draft slot until it materialises).
+	// adapter. setSessionTabs / setSessionPreviewCollapsed stay the low-level record
+	// writers (a transient session's writes land in the localStorage draft slot
+	// until it materialises).
 	const previewTabs = new SessionPreviewTabs(hydratePreviewTabs(session), {
 		persist: (snap) => {
 			setSessionTabs(session.id, snap.tabs, snap.activeId)
 			setSessionPreviewCollapsed(session.id, snap.collapsed)
 		},
-		setTarget: (target) => setSessionTarget(session.id, target)
+		onTabsChanged: pruneEditorCells
 	})
 
 	// Let the jobs tray open a run in this session's preview panel (as an iframe
@@ -376,23 +431,20 @@ function createRuntime(session: Session): SessionRuntime {
 		sessionId: session.id,
 		manager,
 		previewTabs,
-		slot(kind: SessionTargetKind): LoadSlot {
-			return kind === 'flow' ? flowSlot : kind === 'script' ? scriptSlot : rawAppSlot
-		},
 		pipelineEditorState,
-		flowStore,
-		flowStateStore,
-		savedFlow,
+		flowCell,
+		loadedEditorPath,
 
 		async loadFlow(workspace: string, path: string, force = false) {
-			if (flowSlot.loadedPath === path && flowSlot.loadedWorkspace === workspace && !force) return
+			const { slot, store, stateStore, saved } = flowCell(path)
+			if (slot.loadedPath === path && slot.loadedWorkspace === workspace && !force) return
 			// See loadScript: forced reload remounts via the render gate. A workspace
 			// retarget (same path, new fork) drops the stale content the same way so
 			// the editor gate shows loading and outbound sync can't write the old
 			// workspace's content into the new one before the fetch lands.
-			if (force || flowSlot.loadedWorkspace !== workspace) flowSlot.loadedPath = undefined
-			flowSlot.loading = true
-			flowSlot.notFound = false
+			if (force || slot.loadedWorkspace !== workspace) slot.loadedPath = undefined
+			slot.loading = true
+			slot.notFound = false
 			try {
 				// Draft first. UserDraft is the shared authoritative content
 				// source — the chat (write_flow / patch_flow_json /
@@ -416,21 +468,20 @@ function createRuntime(session: Session): SessionRuntime {
 					// yet on the backend — draft-only flows are a valid state.
 					try {
 						const result = await FlowService.getFlowByPath({ workspace, path, getDraft: true })
-						savedFlow.val = result as SavedFlow
+						saved.val = result as SavedFlow
 					} catch {
-						savedFlow.val = undefined
+						saved.val = undefined
 					}
-					await initFlow(aiDraft, flowStore, flowStateStore)
-					if (deployedVersionId != null && flowStore.val)
-						flowStore.val.version_id = deployedVersionId
-					flowSlot.loadedPath = path
-					flowSlot.loadedWorkspace = workspace
+					await initFlow(aiDraft, store, stateStore)
+					if (deployedVersionId != null && store.val) store.val.version_id = deployedVersionId
+					slot.loadedPath = path
+					slot.loadedWorkspace = workspace
 					return
 				}
 
 				// No local draft yet — seed from `result.draft ?? result`.
 				const result = await FlowService.getFlowByPath({ workspace, path, getDraft: true })
-				savedFlow.val = result as SavedFlow
+				saved.val = result as SavedFlow
 				const flow: Flow = ((result as SavedFlow).draft ?? (result as Flow)) as Flow
 				// Seed the per-tab last_sync from the server draft's timestamp so the
 				// seeding save below attaches a matching last_sync and the server can
@@ -443,31 +494,30 @@ function createRuntime(session: Session): SessionRuntime {
 					(result as SavedFlow).draft_saved_at
 				)
 				UserDraft.save('flow', path, flow, { workspace })
-				await initFlow(flow, flowStore, flowStateStore)
-				if (deployedVersionId != null && flowStore.val) flowStore.val.version_id = deployedVersionId
-				flowSlot.loadedPath = path
-				flowSlot.loadedWorkspace = workspace
+				await initFlow(flow, store, stateStore)
+				if (deployedVersionId != null && store.val) store.val.version_id = deployedVersionId
+				slot.loadedPath = path
+				slot.loadedWorkspace = workspace
 			} catch (err) {
 				console.error('Failed to load flow', err)
-				flowSlot.notFound = true
+				slot.notFound = true
 			} finally {
-				flowSlot.loading = false
+				slot.loading = false
 			}
 		},
 
-		scriptStore,
-		savedScript,
+		scriptCell,
 
 		async loadScript(workspace: string, path: string, force = false) {
-			if (scriptSlot.loadedPath === path && scriptSlot.loadedWorkspace === workspace && !force)
-				return
+			const { slot, store, saved } = scriptCell(path)
+			if (slot.loadedPath === path && slot.loadedWorkspace === workspace && !force) return
 			// Forced reload: clearing the slot's loadedPath drops us into
 			// SessionEditorTarget's `{:else if slot.loadedPath === undefined}` gate,
 			// which unmounts then remounts the editor — avoids the Monaco init race a
 			// synchronous {#key} would hit.
-			if (force || scriptSlot.loadedWorkspace !== workspace) scriptSlot.loadedPath = undefined
-			scriptSlot.loading = true
-			scriptSlot.notFound = false
+			if (force || slot.loadedWorkspace !== workspace) slot.loadedPath = undefined
+			slot.loading = true
+			slot.notFound = false
 			try {
 				// Draft first. UserDraft is the shared authoritative content
 				// source — the chat (write_script / edit_script) and the
@@ -482,16 +532,16 @@ function createRuntime(session: Session): SessionRuntime {
 					// savedScript undefined and skip parent_hash.
 					try {
 						const result = await ScriptService.getScriptByPath({ workspace, path, getDraft: true })
-						savedScript.val = result as SavedScript
+						saved.val = result as SavedScript
 					} catch {
-						savedScript.val = undefined
+						saved.val = undefined
 					}
 					// Clone before layering the AI draft on top, else we'd mutate
-					// `savedScript.val` in place and lose the pristine diff baseline.
-					const baseline: NewScript = savedScript.val
+					// `saved.val` in place and lose the pristine diff baseline.
+					const baseline: NewScript = saved.val
 						? (structuredClone(
 								$state.snapshot(
-									(savedScript.val.draft as NewScript | undefined) ?? (savedScript.val as NewScript)
+									(saved.val.draft as NewScript | undefined) ?? (saved.val as NewScript)
 								)
 							) as NewScript)
 						: {
@@ -510,21 +560,21 @@ function createRuntime(session: Session): SessionRuntime {
 								schema: emptySchema(),
 								language: (aiDraft.language ?? 'bun') as any
 							}
-					if (savedScript.val?.hash) {
-						baseline.parent_hash = savedScript.val.hash
+					if (saved.val?.hash) {
+						baseline.parent_hash = saved.val.hash
 					}
 					baseline.content = aiDraft.content
 					if (aiDraft.language) baseline.language = aiDraft.language
 					if (aiDraft.summary !== undefined) baseline.summary = aiDraft.summary
-					scriptStore.val = baseline
-					scriptSlot.loadedPath = path
-					scriptSlot.loadedWorkspace = workspace
+					store.val = baseline
+					slot.loadedPath = path
+					slot.loadedWorkspace = workspace
 					return
 				}
 
 				// No local draft yet — seed from `result.draft ?? result`.
 				const result = await ScriptService.getScriptByPath({ workspace, path, getDraft: true })
-				savedScript.val = result as SavedScript
+				saved.val = result as SavedScript
 				// Clone before mutating, else `baseline` aliases `result` and
 				// `baseline.parent_hash` corrupts the diff baseline.
 				const baseline = structuredClone(
@@ -542,27 +592,26 @@ function createRuntime(session: Session): SessionRuntime {
 					(result as SavedScript).draft_saved_at
 				)
 				UserDraft.save<NewScript>('script', path, baseline, { workspace })
-				scriptStore.val = baseline
-				scriptSlot.loadedPath = path
-				scriptSlot.loadedWorkspace = workspace
+				store.val = baseline
+				slot.loadedPath = path
+				slot.loadedWorkspace = workspace
 			} catch (err) {
 				console.error('Failed to load script', err)
-				scriptSlot.notFound = true
+				slot.notFound = true
 			} finally {
-				scriptSlot.loading = false
+				slot.loading = false
 			}
 		},
 
-		rawApp,
-		savedRawApp,
+		rawAppCell,
 
 		async loadRawApp(workspace: string, path: string, force = false, deployedOnly = false) {
-			if (rawAppSlot.loadedPath === path && rawAppSlot.loadedWorkspace === workspace && !force)
-				return
+			const { slot, store, saved } = rawAppCell(path)
+			if (slot.loadedPath === path && slot.loadedWorkspace === workspace && !force) return
 			// See loadScript: forced reload remounts via the render gate.
-			if (force || rawAppSlot.loadedWorkspace !== workspace) rawAppSlot.loadedPath = undefined
-			rawAppSlot.loading = true
-			rawAppSlot.notFound = false
+			if (force || slot.loadedWorkspace !== workspace) slot.loadedPath = undefined
+			slot.loading = true
+			slot.notFound = false
 			try {
 				// Draft first. UserDraft is the shared authoritative content
 				// source — the chat (init_app / write_app_file / ...) and the
@@ -586,7 +635,7 @@ function createRuntime(session: Session): SessionRuntime {
 						})
 						// Top-level fields are the deployed payload — the diff
 						// baseline, since the session has its own `aiDraft`.
-						savedRawApp.val = {
+						saved.val = {
 							summary: result.summary,
 							value: result.value as any,
 							path: result.path,
@@ -595,9 +644,9 @@ function createRuntime(session: Session): SessionRuntime {
 							no_deployed: result.no_deployed
 						}
 					} catch {
-						savedRawApp.val = undefined
+						saved.val = undefined
 					}
-					rawApp.val = applyDraftToRuntimeRawApp(
+					store.val = applyDraftToRuntimeRawApp(
 						{
 							files: {},
 							runnables: {},
@@ -608,8 +657,8 @@ function createRuntime(session: Session): SessionRuntime {
 						},
 						aiDraft
 					)
-					rawAppSlot.loadedPath = path
-					rawAppSlot.loadedWorkspace = workspace
+					slot.loadedPath = path
+					slot.loadedWorkspace = workspace
 					return
 				}
 
@@ -622,7 +671,7 @@ function createRuntime(session: Session): SessionRuntime {
 					rawApp: true
 				})
 				// Deployed baseline for the diff drawer (top-level fields).
-				savedRawApp.val = {
+				saved.val = {
 					summary: result.summary,
 					value: result.value as any,
 					path: result.path,
@@ -669,14 +718,14 @@ function createRuntime(session: Session): SessionRuntime {
 					(result as any).draft_saved_at as string | undefined
 				)
 				UserDraft.save('raw_app', path, runtimeRawAppToDraft(runtimeValue), { workspace })
-				rawApp.val = runtimeValue
-				rawAppSlot.loadedPath = path
-				rawAppSlot.loadedWorkspace = workspace
+				store.val = runtimeValue
+				slot.loadedPath = path
+				slot.loadedWorkspace = workspace
 			} catch (err) {
 				console.error('Failed to load raw app', err)
-				rawAppSlot.notFound = true
+				slot.notFound = true
 			} finally {
-				rawAppSlot.loading = false
+				slot.loading = false
 			}
 		},
 
@@ -794,33 +843,14 @@ export type SessionChatStatus =
 	| 'draft'
 	| 'error'
 
-// MRU set of session ids whose FlowEditorView is currently mounted. Capped at
-// MAX_WARM_EDITORS — sessions outside the set show chat-only. Module-scoped so
-// both the page (which mutates) and the sidebar (which reads for the dev clue)
-// see the same state.
-const MAX_WARM_EDITORS = 3
-export const editorWarmIds = new SvelteSet<string>()
-
-// Full session teardown: dispose the runtime, drop the LRU entry, and remove
-// from sessionState in one call. Callers (sidebar / header dropdowns) just
-// invoke this; navigation away from a deleted active session is the caller's
-// responsibility.
+// Full session teardown: dispose the runtime and remove from sessionState in one
+// call. Callers (sidebar / header dropdowns) just invoke this; navigation away
+// from a deleted active session is the caller's responsibility.
 export function removeSession(sessionId: string): void {
 	disposeRuntime(sessionId)
-	editorWarmIds.delete(sessionId)
 	deleteSessionState(sessionId)
 }
 
-export function promoteEditorWarm(sessionId: string): void {
-	editorWarmIds.delete(sessionId)
-	editorWarmIds.add(sessionId)
-	while (editorWarmIds.size > MAX_WARM_EDITORS) {
-		const oldest = editorWarmIds.values().next().value
-		if (oldest === undefined) break
-		editorWarmIds.delete(oldest)
-	}
-}
-
 // Register the global open_preview tool handler once at module load. It
 // dispatches to the *calling* session (sessionId threaded from the tool ctx),
 // falling back to the UI-active session only when none was passed — so a
@@ -841,7 +871,6 @@ setOpenPreviewHandler(({ sessionId: callerSessionId, kind, path }) => {
 		return `Error: ${kind} targets cannot be shown in the preview panel.`
 	}
 	const result = getOrCreateRuntime(session).previewTabs.open(target)
-	promoteEditorWarm(sessionId)
 	return result.status === 'focused'
 		? `A preview tab is already showing ${kind} "${path}" — focused it.`
 		: `Opened ${kind} preview for ${path} in a new tab in the side panel.`
@@ -869,12 +898,10 @@ setOpenPagePreviewHandler(({ sessionId: callerSessionId, href, label, newTab })
 			owner.select(existing.id)
 			owner.navigate({ type: 'page', href, label })
 			owner.setCollapsed(false)
-			promoteEditorWarm(sessionId)
 			return `Updated the ${label} preview tab with the new filters.`
 		}
 	}
 	const result = owner.open({ type: 'page', href, label })
-	promoteEditorWarm(sessionId)
 	return result.status === 'focused'
 		? `A preview tab is already showing ${label} — focused it and applied the filters.`
 		: `Opened ${label} in a new preview tab in the side panel.`
@@ -889,7 +916,7 @@ setGetPreviewStatusHandler((callerSessionId) => {
 	const session = sessionState.sessions.find((s) => s.id === sessionId)
 	if (!session) return 'No active session; the preview panel is unavailable.'
 	const owner = getOrCreateRuntime(session).previewTabs
-	return describePreview(owner.tabs, owner.activeId, session.target)
+	return describePreview(owner.tabs, owner.activeId)
 })
 
 // close_page dispatches here to close preview tabs in the calling session's
@@ -923,7 +950,9 @@ setDeployedInSessionHandler(({ sessionId: callerSessionId, kind, path }) => {
 	const session = sessionState.sessions.find((s) => s.id === sessionId)
 	const runtime = runtimes.get(sessionId)
 	if (!session?.workspace_id || !runtime) return
-	if (runtime.slot(kind).loadedPath !== path) return
+	// Peek without creating a cell: a deploy for an item with no open editor tab
+	// must not allocate an empty cell that lingers until the next prune.
+	if (runtime.loadedEditorPath(kind, path) !== path) return
 	runtime.syncPreviewWithDeployed(session.workspace_id, kind, path)
 })
 
diff --git a/frontend/src/lib/components/sessions/sessionState.svelte.ts b/frontend/src/lib/components/sessions/sessionState.svelte.ts
index 7896f6915d..8382c201ce 100644
--- a/frontend/src/lib/components/sessions/sessionState.svelte.ts
+++ b/frontend/src/lib/components/sessions/sessionState.svelte.ts
@@ -37,21 +37,12 @@ import { sendUserToast } from '$lib/toast'
 import type HistoryManager from '$lib/components/copilot/chat/HistoryManager.svelte'
 import { onUserChange, scopedKey } from '$lib/userScopedStorage'
 
-// Kinds the in-session editor pane can host. Legacy drag-and-drop apps are
-// intentionally not previewable — only code-based 'raw_app' apps are. A
-// 'pipeline' target's `path` is the folder name (not a workspace item path):
-// it hosts the data-pipeline graph editor for that folder, which uses its own
-// fetch/draft model rather than the single-item load slots the other kinds share.
+// A destination the session preview can open as an editor: a workspace item
+// (`path`) for flow/script/raw_app, or — for 'pipeline' — a folder name (not an
+// item path), which resolves to the data-pipeline graph editor for that folder.
+// Legacy drag-and-drop apps aren't previewable; only code-based 'raw_app' apps.
 export type SessionTarget = { kind: 'flow' | 'script' | 'raw_app' | 'pipeline'; path: string }
 
-// Useful for filtering dropdowns / pickers to "items the side panel can open".
-export const EDITOR_TARGET_KINDS: ReadonlySet<SessionTarget['kind']> = new Set([
-	'flow',
-	'script',
-	'raw_app',
-	'pipeline'
-])
-
 // Whether the session points at a workspace that is itself a fork (i.e.
 // has a parent). Used by the sidebar to pick between a root (Building)
 // icon and a fork icon.
@@ -97,7 +88,6 @@ export type Session = {
 	// workspace_id, not this field. Root sessions store the same id in both fields.
 	workspace_root_id?: string
 	chatId?: string
-	target?: SessionTarget
 	summary?: string
 	summarySource?: SessionSummarySource
 	createdAt: number
@@ -151,12 +141,12 @@ interface SessionSchema extends DBSchema {
 }
 
 // Normalise legacy localStorage records in place: drop empty-string
-// workspace_id (older drafts used '' as a missing marker), migrate the
-// deprecated 'rawapp' target.kind, and coerce unknown summarySource values.
-// Operates on raw parsed JSON, so the record is loosely typed.
+// workspace_id (older drafts used '' as a missing marker), drop the retired
+// `target` field (the preview is tab-driven now), and coerce unknown
+// summarySource values. Operates on raw parsed JSON, so the record is loosely typed.
 function normalizeLegacySession(s: Record<string, any>): void {
 	if (s.workspace_id === '') delete s.workspace_id
-	if (s.target?.kind === 'rawapp') s.target.kind = 'raw_app'
+	delete s.target
 	if (
 		s.summarySource !== undefined &&
 		s.summarySource !== 'placeholder' &&
@@ -804,20 +794,6 @@ export function getEffectiveWorkspaceId(session: Session): string | undefined {
 	return session.workspace_id ?? session.pending_workspace_id
 }
 
-// Canonical mutation for session.target. Persists, optionally seeds the
-// session summary, and centralises the path so callers don't reach into
-// session.target directly.
-export function setSessionTarget(id: string, target: SessionTarget, summary?: string): void {
-	const s = sessionState.sessions.find((x) => x.id === id)
-	if (!s) return
-	s.target = target
-	if (!s.summary && summary) {
-		s.summary = summary
-		s.summarySource = 'generated'
-	}
-	void putSession(s)
-}
-
 // Persist the session's preview tabs. Fire-and-forget write-behind (transient
 // sessions land in the localStorage draft slot).
 export function setSessionTabs(id: string, tabs: SessionPreviewTab[], activeTabId: string): void {
diff --git a/frontend/src/lib/components/sessions/sessionStateIndexedDb.test.ts b/frontend/src/lib/components/sessions/sessionStateIndexedDb.test.ts
index 2ebe031597..131a299082 100644
--- a/frontend/src/lib/components/sessions/sessionStateIndexedDb.test.ts
+++ b/frontend/src/lib/components/sessions/sessionStateIndexedDb.test.ts
@@ -123,7 +123,6 @@ describe('sessionState IndexedDB persistence', () => {
 			session({
 				id: 't1b',
 				transient: true,
-				target: { kind: 'script', path: 'u/me/foo' },
 				previewTabs: [{ id: 'session', url: '/x', loc: '/x' }],
 				activePreviewTabId: 'session',
 				previewCollapsed: false
@@ -132,7 +131,6 @@ describe('sessionState IndexedDB persistence', () => {
 		await rehydrate(user)
 		await flush()
 		const restored = sessionState.sessions.find((s) => s.id === 't1b')
-		expect(restored?.target).toEqual({ kind: 'script', path: 'u/me/foo' })
 		expect(restored?.previewTabs).toEqual([{ id: 'session', url: '/x', loc: '/x' }])
 		expect(restored?.activePreviewTabId).toBe('session')
 		expect(restored?.previewCollapsed).toBe(false)
diff --git a/frontend/src/lib/components/sessions/sessionSwitch.svelte.ts b/frontend/src/lib/components/sessions/sessionSwitch.svelte.ts
index e045632e3c..45d72ae3ae 100644
--- a/frontend/src/lib/components/sessions/sessionSwitch.svelte.ts
+++ b/frontend/src/lib/components/sessions/sessionSwitch.svelte.ts
@@ -7,7 +7,6 @@ import {
 	sessionInCurrentFamily,
 	sessionState,
 	setSessionPendingWorkspace,
-	setSessionTarget,
 	type SessionTarget
 } from './sessionState.svelte'
 import { sessionTargetHref } from './sessionMode.svelte'
@@ -66,8 +65,8 @@ export async function exitSessionMode(): Promise<void> {
 	await goto(target)
 }
 
-// Open a fresh AI session pre-targeted at an editor (flow/script/raw_app), then
-// route into session mode. The session preview loads that editor via its target,
+// Open a fresh AI session showing an editor (flow/script/raw_app) in its preview,
+// then route into session mode. The preview loads the item from its live draft,
 // so the caller MUST persist any unsaved edits first (e.g. save a draft) for the
 // preview to reflect the live state. `workspaceId` scopes the session to the
 // editor's workspace (instead of createSession's root default) so it opens the
@@ -76,16 +75,14 @@ export async function openEditorInSession(
 	target: SessionTarget,
 	workspaceId?: string
 ): Promise<void> {
-	// createSession() reuses an existing transient draft, which may still be
-	// pointed at a *different* item — and its preview tabs (persisted with the
-	// draft and/or held by a live runtime) keep showing that old target unless
-	// the tab model is reset along with the target field.
+	// createSession() reuses an existing transient draft, whose preview tabs
+	// (persisted with the draft and/or held by a live runtime) may still show a
+	// different item — so seed the preview with a single tab on `target`, resetting
+	// whatever it was showing.
 	const session = createSession()
-	const retargeted = session.target?.kind !== target.kind || session.target?.path !== target.path
 	if (workspaceId) setSessionPendingWorkspace(session.id, workspaceId)
-	setSessionTarget(session.id, target)
 	const url = sessionTargetHref(target)
-	if (url && retargeted) {
+	if (url) {
 		// Dynamic import: a static one would drag the runtime's heavy graph
 		// (chat manager → monaco) into this thin navigation seam, breaking its
 		// node-run unit tests.
diff --git a/frontend/src/lib/components/sessions/useUserDraftSync.svelte.ts b/frontend/src/lib/components/sessions/useUserDraftSync.svelte.ts
index e5af840242..7e89d3b945 100644
--- a/frontend/src/lib/components/sessions/useUserDraftSync.svelte.ts
+++ b/frontend/src/lib/components/sessions/useUserDraftSync.svelte.ts
@@ -37,7 +37,13 @@ export interface UserDraftSyncOptions<Draft> {
 	 * `loadedX !== path` guards.
 	 */
 	ready: () => boolean
-	codec: DraftSyncCodec<Draft>
+	/**
+	 * Reactive codec. Retargeting a mounted editor (breadcrumb / in-editor link)
+	 * changes `path` without remounting, and the codec closes over one
+	 * `(kind, path)` cell's store — so it must be re-read per path, not captured
+	 * once, or the sync would read/write the previously-targeted cell.
+	 */
+	codec: () => DraftSyncCodec<Draft>
 }
 
 /**
@@ -61,18 +67,19 @@ export interface UserDraftSyncOptions<Draft> {
  * Must be called once during component init (registers `useMany` + two `$effect`s).
  */
 export function useUserDraftSync<Draft>(opts: UserDraftSyncOptions<Draft>): void {
-	const { codec } = opts
 	const handles = UserDraft.useMany<Draft>(() => {
 		const p = opts.path()
 		const ws = opts.workspace()
-		return p && ws ? [{ itemKind: codec.itemKind, path: p, workspace: ws }] : []
+		return p && ws ? [{ itemKind: opts.codec().itemKind, path: p, workspace: ws }] : []
 	})
 	let lastInboundSig: string | undefined = $state(undefined)
 
 	// inbound: handle.draft → store. Re-runs when the handle's draft changes
-	// (chat write / another session's edit). The store read happens inside
-	// applyDraftToStore under untrack so the editor's own mutations don't refire.
+	// (chat write / another session's edit) or the target retargets (new codec).
+	// The store read happens inside applyDraftToStore under untrack so the
+	// editor's own mutations don't refire.
 	$effect(() => {
+		const codec = opts.codec()
 		const incoming = handles[0]?.draft
 		if (incoming == null) return
 		const sig = codec.sig(incoming)
@@ -101,6 +108,7 @@ export function useUserDraftSync<Draft>(opts: UserDraftSyncOptions<Draft>): void
 	let pendingFlush: (() => void) | undefined
 	$effect(() => {
 		if (!opts.ready()) return
+		const codec = opts.codec()
 		const draft = codec.storeToDraft(undefined)
 		if (draft == null) return
 		const sig = codec.sig(draft)
diff --git a/frontend/src/routes/(root)/(logged)/sessions/+page.svelte b/frontend/src/routes/(root)/(logged)/sessions/+page.svelte
index 232f2fb003..6571e6a1b3 100644
--- a/frontend/src/routes/(root)/(logged)/sessions/+page.svelte
+++ b/frontend/src/routes/(root)/(logged)/sessions/+page.svelte
@@ -38,8 +38,7 @@
 	import {
 		getOrCreateRuntime,
 		getRuntime,
-		listRuntimes,
-		promoteEditorWarm
+		listRuntimes
 	} from '$lib/components/sessions/sessionRuntime.svelte'
 	import { markSessionSeen } from '$lib/components/sessions/sessionUnread.svelte'
 	import { isGlobalAiEnabled } from '$lib/components/copilot/chat/global/gate'
@@ -52,6 +51,7 @@
 		previewLocationLabel,
 		type PreviewTarget
 	} from '$lib/components/sessions/previewRouter'
+	import { toolReloadEffect, tabsToReload } from '$lib/components/sessions/previewReload'
 	import { leafKeyFor, type WorkspaceItem } from '$lib/components/workspacePicker'
 	import { splitterPointerCapture } from '$lib/utils/splitterPointerCapture'
 
@@ -132,14 +132,6 @@
 			.filter((s): s is NonNullable<typeof s> => s != null)
 	)
 
-	// Promote the active session in the LRU. Mutations untracked so the effect
-	// only re-runs when activeSession changes, not on its own writes.
-	$effect(() => {
-		const id = activeSession?.id
-		if (!id) return
-		untrack(() => promoteEditorWarm(id))
-	})
-
 	// Mark the active session "seen" up to its current message count: arrive →
 	// clear unread; AI streams a new message while we're here → clear again. The
 	// effect depends only on the length, not the array contents, so token-by-token
@@ -317,61 +309,49 @@
 		}
 	}
 
-	// Reload mounted preview tabs affected by a mutating chat tool (write_/patch_/
-	// delete_/deploy_/…; read/test/navigate tools don't match). Scoped to the changed
-	// item so editing one item never blank-reboots an unrelated item's preview iframe
-	// (a full-page /apps_raw/edit reload is jarring).
+	// Reload mounted preview tabs affected by a mutating chat tool. Item and pipeline
+	// tabs are live editors that self-sync from the store the chat mutates, so nothing
+	// reloads them. Only list-page tabs (schedules, resources, …) are iframes, and each
+	// reloads only when a tool actually changed *its* page (toolReloadEffect) — so a
+	// schedule write leaves the Resources tab alone, and a purely local tool (saving
+	// user instructions) reloads nothing.
 	const tabHosts: Record<string, PreviewTabHost | undefined> = {}
-	const MUTATING_TOOL_RE = /^(write_|patch_|delete_|deploy_|discard_|set_|create_|update_|remove_)/
-	let reloadHandle: ReturnType<typeof setTimeout> | undefined
-	// Drained each flush: item paths touched since the last flush, and a flag for an
-	// unresolved mutation that forces a full reload (safe fallback).
-	let pendingReloadPaths = new Set<string>()
-	let pendingReloadAll = false
 
-	// Reload the batched-mutation tabs across all warm sessions' mounted tabs (a
-	// hidden preview would otherwise show pre-mutation content on return). `null`
-	// reloads all; otherwise an item-route iframe reloads only when its item was
-	// touched. Non-item pages always reload; a live-editor slot no-ops in reload().
-	function reloadTabs(paths: Set<string> | null) {
+	let reloadHandle: ReturnType<typeof setTimeout> | undefined
+	// Base-stripped list-page paths (e.g. `/schedules`) a chat round touched since
+	// the last flush — see toolReloadEffect for how tools map to pages.
+	let pendingPages = new Set<string>()
+
+	// Reload the mounted list-page tabs a chat round changed, across all warm
+	// sessions (a hidden preview would otherwise show pre-mutation content on
+	// return). tabsToReload picks only the tabs whose page is in `pages`.
+	function reloadTabs(pages: Set<string>) {
 		for (const s of warmSessions) {
-			const tabs = getRuntime(s.id)?.previewTabs?.tabs ?? []
-			for (const tab of tabs) {
+			const owner = getRuntime(s.id)?.previewTabs
+			if (!owner) continue
+			for (const tab of tabsToReload(owner.tabs, pages)) {
 				const key = tabKey(s.id, tab.id)
-				if (!mountedTabKeys.has(key)) continue
-				if (paths) {
-					const route = parsePreviewItemRoute(tab.url)
-					if (route && !paths.has(route.itemPath)) continue
-				}
-				tabHosts[key]?.reload()
+				if (mountedTabKeys.has(key)) tabHosts[key]?.reload()
 			}
 		}
 	}
 	function flushReload() {
-		const paths = pendingReloadAll ? null : pendingReloadPaths
-		pendingReloadPaths = new Set()
-		pendingReloadAll = false
-		reloadTabs(paths)
+		const pages = pendingPages
+		pendingPages = new Set()
+		reloadTabs(pages)
 	}
 	$effect(() => {
 		// Debounced so a burst of writes (the AI editing several files) reloads once.
 		setToolCompletionListener((name, args) => {
-			if (!MUTATING_TOOL_RE.test(name)) return
-			// A workspace item path scopes the reload to that item. The raw-app file
-			// tools (write_app_file, …) pass a leading-'/' frontend file path and edit
-			// the active session's target app, so scope to the target. Anything else is
-			// unresolved → reload everything (safe fallback).
-			const p = typeof args?.path === 'string' ? args.path : undefined
-			if (p && !p.startsWith('/')) pendingReloadPaths.add(p)
-			else if (p && activeSession?.target?.path) pendingReloadPaths.add(activeSession.target.path)
-			else pendingReloadAll = true
+			const { pages } = toolReloadEffect(name, args)
+			if (pages.length === 0) return
+			for (const p of pages) pendingPages.add(p)
 			clearTimeout(reloadHandle)
 			reloadHandle = setTimeout(flushReload, 500)
 		})
 		return () => {
 			clearTimeout(reloadHandle)
-			pendingReloadPaths = new Set()
-			pendingReloadAll = false
+			pendingPages = new Set()
 			setToolCompletionListener(undefined)
 		}
 	})
@@ -565,7 +545,7 @@
 										: 'z-0 opacity-0 pointer-events-none'}"
 									aria-hidden={s.id !== activeSession?.id}
 								>
-									<SessionWrapper sessionId={s.id} hideEditor />
+									<SessionWrapper sessionId={s.id} />
 								</div>
 							{/each}
 						</div>