diff --git a/frontend/src/lib/components/copilot/chat/AIChatManager.svelte.ts b/frontend/src/lib/components/copilot/chat/AIChatManager.svelte.ts
index 25179abe5d..f4abb93830 100644
--- a/frontend/src/lib/components/copilot/chat/AIChatManager.svelte.ts
+++ b/frontend/src/lib/components/copilot/chat/AIChatManager.svelte.ts
@@ -507,6 +507,11 @@ export class AIChatManager implements ChatViewHost {
 	// awaits this so the model's next build_pipeline_node call can't race ahead of
 	// the async canvas mount and hit "Unknown tool call".
 	#pipelineHelpersWaiters = new Set<(helpers: PipelineAIChatHelpers) => void>()
+	// A session's pipeline editor unmounts whenever another tab takes the preview
+	// panel. Its tools stay offered for every folder the session opened, and a call
+	// reopens the tab through this, so a page shown in between costs no failed call.
+	#pipelineReopener: ((folder: string) => void) | undefined = undefined
+	#openedPipelineFolders = new Set<string>()
 	readonly isOpen = $derived(chatState.size > 0)
 	savedSize = $state<number>(0)
 	instructions = $state<string>('')
@@ -2504,8 +2509,27 @@ export class AIChatManager implements ChatViewHost {
 
 	// Public because it is purely local, unlike `changeMode(GLOBAL)`, which also
 	// fires the three network refreshes.
+	setPipelineReopener = (reopen: (folder: string) => void) => {
+		this.#pipelineReopener = reopen
+	}
+
+	#pipelineFolders = (): string[] => [
+		...new Set([
+			...[...this.#pipelineEditors].map((p) => p.getFolder()),
+			...(this.#pipelineReopener ? this.#openedPipelineFolders : [])
+		])
+	]
+
+	#ensurePipeline = async (folder: string): Promise<PipelineAIChatHelpers | undefined> => {
+		const find = () => [...this.#pipelineEditors].find((p) => p.getFolder() === folder)
+		const live = find()
+		if (live || !this.#pipelineReopener) return live
+		this.#pipelineReopener(folder)
+		return (await this.waitForPipelineHelpers(folder)) ? find() : undefined
+	}
+
 	configureGlobalMode = () => {
-		const hasPipelines = this.#pipelineEditors.size > 0
+		const hasPipelines = this.#pipelineFolders().length > 0
 		const opts = this.globalAssemblyOpts()
 		const baseHelpers: GlobalToolHelpers = {
 			// A session targets its own fixed (possibly forked) workspace, so capture it for
@@ -2538,7 +2562,12 @@ export class AIChatManager implements ChatViewHost {
 		}
 		this.#assembledTools = assembleGlobalTools(opts)
 		this.helpers = hasPipelines
-			? { ...baseHelpers, pipelines: () => [...this.#pipelineEditors] }
+			? {
+					...baseHelpers,
+					pipelines: () => [...this.#pipelineEditors],
+					pipelineFolders: this.#pipelineFolders,
+					ensurePipeline: this.#ensurePipeline
+				}
 			: baseHelpers
 		this.systemMessage = assembleGlobalSystemMessage(getCustomPromptParts(AIMode.GLOBAL), opts)
 		this.syncArtifactsSession()
@@ -2552,7 +2581,7 @@ export class AIChatManager implements ChatViewHost {
 		mcpServers: this.mcpServers,
 		access: this.sessionAccess,
 		sessionContext: this.sessionContextResolver?.(),
-		pipelineFolders: [...new Set([...this.#pipelineEditors].map((p) => p.getFolder()))]
+		pipelineFolders: this.#pipelineFolders()
 	})
 
 	// Fetch the workspace's AI skills and, if GLOBAL mode is still active, rebuild
@@ -4885,6 +4914,7 @@ export class AIChatManager implements ChatViewHost {
 	// Returns a cleanup that tears the registration back down.
 	setPipelineHelpers = (pipelineHelpers: PipelineAIChatHelpers) => {
 		this.#pipelineEditors.add(pipelineHelpers)
+		this.#openedPipelineFolders.add(pipelineHelpers.getFolder())
 		untrack(() => {
 			if (this.mode === AIMode.GLOBAL) {
 				this.configureGlobalMode()
diff --git a/frontend/src/lib/components/copilot/chat/global/core.ts b/frontend/src/lib/components/copilot/chat/global/core.ts
index b714636875..8856877d9c 100644
--- a/frontend/src/lib/components/copilot/chat/global/core.ts
+++ b/frontend/src/lib/components/copilot/chat/global/core.ts
@@ -1477,7 +1477,7 @@ ${pipelineBullet}`
 					canWriteDraft,
 					`
 - After writing or substantially editing a script / flow / app draft, show it via open_preview(kind, path) so the user sees the editor and live preview right next to the chat. First check whether it is already shown: if unsure, call get_preview_status. Only call open_preview (or offer to) when no preview is open or it is showing a different item — don't re-open a preview already showing the item you just edited.
-- Building a data pipeline: call open_preview(kind="pipeline", path="<folder>") as the FIRST step, before creating any node — this opens the pipeline editor the user reviews in. path is the folder, not an item; an empty ${when(canCreateFolder, 'or not-yet-created ')}folder is fine${when(canCreateFolder, ' (create_folder first if needed, then open it)')}. Opening it adds build_pipeline_node / edit_pipeline_node to your tools from the next step on — they are not in your tool list before open_preview returns, so call open_preview on its own, wait for its result, then build. Use ONLY those to add or change pipeline nodes, never write_script for a pipeline node — they apply directly as unsaved drafts on the canvas (no separate accept/reject step) that the user reviews and deploys. Do not write pipeline scripts without first opening the editor.`
+- Building a data pipeline: call open_preview(kind="pipeline", path="<folder>") as the FIRST step, before creating any node — this opens the pipeline editor the user reviews in. path is the folder, not an item; an empty ${when(canCreateFolder, 'or not-yet-created ')}folder is fine${when(canCreateFolder, ' (create_folder first if needed, then open it)')}. Opening it adds build_pipeline_node / edit_pipeline_node to your tools from the next step on — they are not in your tool list before open_preview returns, so call open_preview on its own, wait for its result, then build. They then stay available for the rest of the session even while another tab (a page, another preview) is shown: a call brings the pipeline editor back by itself, so do not re-open it first. Use ONLY those to add or change pipeline nodes, never write_script for a pipeline node — they apply directly as unsaved drafts on the canvas (no separate accept/reject step) that the user reviews and deploys. Do not write pipeline scripts without first opening the editor.`
 				)}
 - When debugging a running raw app, call get_app_runtime_logs to read the live preview's browser console output. It needs the raw app preview open (open_preview kind="raw_app").
 - Writing an app file does not compile it: the open preview rebuilds it afterwards. After editing a raw app's frontend files with its preview open, call get_app_runtime_logs to check the build — when it failed, it returns the build errors (e.g. syntax or import errors) and bundler logs to fix.
diff --git a/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts b/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts
index 958414dcd1..1aa7b7ef78 100644
--- a/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts
+++ b/frontend/src/lib/components/sessions/sessionRuntime.svelte.ts
@@ -634,6 +634,10 @@ function createRuntime(session: Session): SessionRuntime {
 			waiters.add(notify)
 		})
 	}
+	manager.setPipelineReopener((folder) => {
+		const target = previewTargetForSessionTarget('pipeline', folder)
+		if (target) previewTabs.open(target)
+	})
 	async function deployPipeline(folder: string): Promise<DeployResult> {
 		const key = normalizePipelineFolder(folder)
 		const target = previewTargetForSessionTarget('pipeline', key)