perf(terminal): keep unviewed restart survivors to the daemon's live window

Main now attaches every surviving terminal at startup; each mirror took the full
5,000-row depth with no viewer. A survivor nobody views keeps the 1,000 rows the
daemon itself holds, and grows to full depth from those rows once a view subscribes.

src/main/daemon/headless-emulator.ts

@@ -23,7 +23,7 @@ import {
   type TerminalViewAttributeResponder
 } from './terminal-view-attribute-responder'
 import { installDeviceAttributesResponder } from './startup-device-attributes-responder'
-import type { TerminalSnapshot, TerminalModes } from './types'
+import type { TerminalSnapshot } from './types'
 import type { TerminalOscLinkRange } from '../../shared/terminal-osc-link-ranges'
 import type { TerminalCursorContext } from '../../shared/terminal-composer-draft'
 import { readTerminalCursorLineContext } from '../../shared/terminal-cursor-line-context'
@@ -241,7 +241,7 @@ export class HeadlessEmulator {
   }
 
   getSnapshot(opts: { scrollbackRows?: number } = {}): TerminalSnapshot {
-    const modes = this.getModes()
+    const modes = readTerminalModes(this.terminal)
     // Absolute cursor restore avoids wrap-pending drift; carry the saved register for DECRC.
     const serializedAnsi = serializeWithAbsoluteCursor(
       this.serializer,
@@ -345,6 +345,11 @@ export class HeadlessEmulator {
     this.restoredOscLinks = links?.slice() ?? []
   }
 
+  /** Growing keeps every retained row; shrinking drops the oldest. */
+  setScrollback(rows: number): void {
+    this.terminal.options.scrollback = rows
+  }
+
   clearScrollback(): void {
     this.restoredOscLinks = []
     this.terminal.clear()
@@ -354,8 +359,4 @@ export class HeadlessEmulator {
     this.disposed = true
     this.terminal.dispose()
   }
-
-  private getModes(): TerminalModes {
-    return readTerminalModes(this.terminal)
-  }
 }

src/main/runtime/terminal-subscriber-driven-daemon-attach.test.ts

@@ -13,6 +13,7 @@ import {
   encodeTerminalStreamFrame,
   encodeTerminalStreamJson
 } from '../../shared/terminal-stream-protocol'
+import { DAEMON_SESSION_SCROLLBACK_ROWS } from '../daemon/daemon-session-scrollback-window'
 
 const WORKTREE_ID = 'repo-1::/tmp/wt'
 const PTY_ID = `${WORKTREE_ID}@@1a2b3c4d`
@@ -24,7 +25,7 @@ type RuntimeInternals = {
     state?: { connected?: boolean; connectionId?: string | null }
   ) => unknown
   issuePtyHandle: (pty: unknown) => string
-  headlessTerminals: Map<string, unknown>
+  headlessTerminals: Map<string, { writeChain: Promise<unknown> }>
   refreshPtyWorktreeRecordsWithControllerInventory: (
     worktrees: [],
     targetWorktreeId: string | null
@@ -263,6 +264,19 @@ function snapshotText(harness: ReturnType<typeof startMultiplex>): string {
     .join('')
 }
 
+function numberedLines(from: number, to: number): string {
+  return Array.from(
+    { length: to - from + 1 },
+    (_, i) => `L${String(from + i).padStart(4, '0')}`
+  ).join('\r\n')
+}
+
+async function retainedLines(runtime: OrcaRuntimeService, ptyId: string): Promise<string[]> {
+  await internals(runtime).headlessTerminals.get(ptyId)?.writeChain
+  const snapshot = await runtime.serializeMainTerminalBuffer(ptyId, { scrollbackRows: 10_000 })
+  return `${snapshot?.scrollbackAnsi ?? ''}${snapshot?.data ?? ''}`.match(/L\d{4}/g) ?? []
+}
+
 describe('subscriber-driven daemon attach (never-activated tab)', () => {
   it('attaches on first desktop multiplex subscribe and streams bytes (snapshot-null daemon)', async () => {
     const { runtime, model, handle, mountSpy } = setupNeverAttachedDaemonSession({
@@ -431,6 +445,43 @@ describe('subscriber-driven daemon attach (never-activated tab)', () => {
     expect(read.tail.join('\n')).toContain('worker still printing')
   })
 
+  it('keeps unviewed survivors to the daemon window and grows a viewed one from it', async () => {
+    const runtime = new OrcaRuntimeService()
+    const model = createDaemonProviderModel({ snapshotCapable: false })
+    model.bind(runtime)
+    runtime.setPtyController(model.controller as never)
+    const ptyIds = Array.from({ length: 10 }, (_, i) => `${WORKTREE_ID}@@0000000${i}`)
+    const records = ptyIds.map((ptyId) => {
+      model.sessions.set(ptyId, { cols: 137, rows: 41, attached: false, screen: '' })
+      return internals(runtime).recordPtyWorktree(ptyId, WORKTREE_ID, { connected: true })
+    })
+    await internals(runtime).refreshPtyWorktreeRecordsWithControllerInventory([], null)
+    await vi.waitFor(() => expect(model.attachCalls).toHaveLength(10))
+
+    for (const ptyId of ptyIds) {
+      expect(model.emitData(ptyId, numberedLines(1, 3000))).toBe(true)
+    }
+    const retained = await Promise.all(ptyIds.map((ptyId) => retainedLines(runtime, ptyId)))
+    const windowRows = DAEMON_SESSION_SCROLLBACK_ROWS + 41
+    expect(retained.map((lines) => lines.length)).toEqual(ptyIds.map(() => windowRows))
+    expect(retained[0].at(-1)).toBe('L3000')
+
+    // The first view paints exactly the rows the mirror kept, then the mirror grows past the window.
+    const harness = startMultiplex(runtime)
+    await vi.waitFor(() => expect(harness.handlers.has(0)).toBe(true))
+    sendSubscribe(harness, 1, internals(runtime).issuePtyHandle(records[0]))
+    await waitForSubscribed(harness, 1)
+    expect(snapshotText(harness).match(/L\d{4}/g)).toEqual(retained[0])
+    model.emitData(ptyIds[0], `\r\n${numberedLines(3001, 6000)}`)
+    model.emitData(ptyIds[1], `\r\n${numberedLines(3001, 6000)}`)
+    await vi.waitFor(() => expect(outputText(harness)).toContain('L6000'))
+    expect(await retainedLines(runtime, ptyIds[0])).toEqual([
+      ...retained[0],
+      ...numberedLines(3001, 6000).split('\r\n')
+    ])
+    expect(await retainedLines(runtime, ptyIds[1])).toHaveLength(windowRows)
+  })
+
   it('does not subscriber-attach or provider-read a session this app already spawned', async () => {
     const { runtime, model, handle } = setupNeverAttachedDaemonSession({
       snapshotCapable: true,

src/main/runtime/terminal/layout/terminal-view-presence.ts

@@ -41,6 +41,10 @@ export abstract class OrcaRuntimeWithNotifyRemoteTerminalViewPresenceChanged ext
   ): Promise<WriteSettlement | undefined>
 
   protected notifyRemoteTerminalViewPresenceChanged(ptyId: string): void {
+    // A viewed survivor's mirror grows to full depth from the rows it kept.
+    if (this.hasTerminalViewer(ptyId) && this.unviewedSurvivorMirrorPtys.delete(ptyId)) {
+      this.headlessTerminals.get(ptyId)?.emulator.setScrollback(this.headlessTerminalScrollbackRows)
+    }
     try {
       this.onRemoteTerminalViewPresenceChanged?.(ptyId)
     } catch (err) {

src/main/runtime/terminal/lifecycle/pty-controller-inventory-refresh.ts

@@ -190,6 +190,12 @@ export abstract class OrcaRuntimeWithRefreshPtyWorktreeRecordsWithControllerInve
           this.restoredOrchestrationAuthorityByPtyId.delete(session.id)
         }
         pty.controllerTitle = session.title?.trim() || null
+        if (
+          !this.hasTerminalViewer(session.id) &&
+          this.mainDaemonAttachments.isKnownUnattachedLocal(session.id)
+        ) {
+          this.unviewedSurvivorMirrorPtys.add(session.id)
+        }
         this.mainDaemonAttachments.reconcile(session.id)
       }
       // Do not serialize relay probes or let one throw abort inventory cleanup.

src/main/runtime/terminal/lifecycle/pty-exit-lifecycle.ts

@@ -162,6 +162,7 @@ export abstract class OrcaRuntimeWithOnPtyExit extends OrcaRuntimeWithOnClientDi
       this.mobileSubscribers.delete(ptyId)
       this.terminalViewSubscribers.clearSubscribers(ptyId)
       this.mainDaemonAttachments.forget(ptyId)
+      this.unviewedSurvivorMirrorPtys.delete(ptyId)
       this.mobileDisplayModes.delete(ptyId)
       this.resizeListeners.delete(ptyId)
       this.lastRendererSizes.delete(ptyId)

src/main/runtime/terminal/lifecycle/terminal-view-resources.ts

@@ -53,6 +53,9 @@ export abstract class OrcaRuntimeWithFitOverrideListeners extends OrcaRuntimeWit
 
   protected providerSnapshotPreferredPtys = new Set<string>()
 
+  // Survivors main attached with no view hold the daemon's live window, not a full-depth copy.
+  protected unviewedSurvivorMirrorPtys = new Set<string>()
+
   protected providerModeTrackersByPtyId = new Map<string, TerminalKittyKeyboardModeTracker>()
 
   protected providerModeSnapshotScansByPtyId = new Map<

src/main/runtime/terminal/output/headless-terminal-state.ts

@@ -1,6 +1,7 @@
 import { OrcaRuntimeWithMaybeHydrateHeadlessFromRenderer } from './headless-terminal-hydration'
 import type { RuntimeHeadlessTerminal } from '../../runtime-terminal-state-records'
 import { HeadlessEmulator } from '../../../daemon/headless-emulator'
+import { DAEMON_SESSION_SCROLLBACK_ROWS } from '../../../daemon/daemon-session-scrollback-window'
 import { shouldForwardHeadlessTerminalQueryReply } from '../../headless-terminal-query-reply-policy'
 import { isNativeWindowsConptyPty } from '../../terminal-model-query-authority'
 import { getTerminalViewAttributes } from '../../terminal-view-attribute-store'
@@ -41,7 +42,9 @@ export abstract class OrcaRuntimeWithCreatePtyHeadlessTerminalState extends Orca
     const emulator = new HeadlessEmulator({
       cols: dims.cols,
       rows: dims.rows,
-      scrollback: this.headlessTerminalScrollbackRows,
+      scrollback: this.unviewedSurvivorMirrorPtys.has(ptyId)
+        ? Math.min(DAEMON_SESSION_SCROLLBACK_ROWS, this.headlessTerminalScrollbackRows)
+        : this.headlessTerminalScrollbackRows,
       pathFlavor,
       remotePosixFileUriAuthority:
         !!this.ptysById.get(ptyId)?.connectionId && pathFlavor !== 'win32',