fix(daemon): bound durable snapshot replay

src/main/daemon/daemon-durable-history-snapshot.ts

@@ -23,7 +23,7 @@ export function terminalSnapshotFromColdRestore(
 ): TerminalSnapshot {
   return {
     snapshotAnsi: info.snapshotAnsi,
-    scrollbackAnsi: info.scrollbackAnsi,
+    scrollbackAnsi: info.modes.alternateScreen ? info.scrollbackAnsi : '',
     oscLinks: info.oscLinks,
     rehydrateSequences: info.rehydrateSequences,
     ...(info.pendingEscapeTailAnsi ? { pendingEscapeTailAnsi: info.pendingEscapeTailAnsi } : {}),
@@ -42,12 +42,17 @@ export async function buildDurableCheckpointSnapshot(opts: {
   liveSnapshot: TerminalSnapshot
   restoreInfo: ColdRestoreInfo | null
   pendingRecords?: readonly PendingOutputRecord[]
+  scrollbackRows?: number
 }): Promise<TerminalSnapshot> {
   const pendingRecords = opts.pendingRecords ?? []
   if (!opts.restoreInfo && pendingRecords.length === 0) {
     return opts.liveSnapshot
   }
-  if (opts.restoreInfo && pendingRecords.length === 0) {
+  if (
+    opts.restoreInfo &&
+    pendingRecords.length === 0 &&
+    (opts.scrollbackRows === undefined || opts.scrollbackRows >= DAEMON_RESTORE_SCROLLBACK_ROWS)
+  ) {
     return terminalSnapshotFromColdRestore(opts.restoreInfo, {
       outputSequence: opts.liveSnapshot.outputSequence,
       frameRestoreAnsi: opts.liveSnapshot.frameRestoreAnsi
@@ -57,7 +62,10 @@ export async function buildDurableCheckpointSnapshot(opts: {
   const emulator = new HeadlessEmulator({
     cols: opts.restoreInfo?.cols ?? opts.liveSnapshot.cols,
     rows: opts.restoreInfo?.rows ?? opts.liveSnapshot.rows,
-    scrollback: DAEMON_RESTORE_SCROLLBACK_ROWS
+    scrollback: Math.min(
+      opts.scrollbackRows ?? DAEMON_RESTORE_SCROLLBACK_ROWS,
+      DAEMON_RESTORE_SCROLLBACK_ROWS
+    )
   })
   const replay = new ColdRestoreReplayWriter(emulator)
   try {
@@ -104,7 +112,7 @@ export async function buildDurableCheckpointSnapshot(opts: {
 
 function restoreBaseFrom(restoreInfo: ColdRestoreInfo): RestoreBase {
   return {
-    scrollbackAnsi: restoreInfo.scrollbackAnsi,
+    scrollbackAnsi: restoreInfo.modes.alternateScreen ? restoreInfo.scrollbackAnsi : '',
     rehydrateSequences: restoreInfo.rehydrateSequences,
     snapshotAnsi: restoreInfo.snapshotAnsi,
     ...(restoreInfo.pendingEscapeTailAnsi

src/main/daemon/daemon-pty-adapter.ts

@@ -70,6 +70,7 @@ import { resolveSafePtyDefaultCwd } from '../providers/pty-default-cwd'
 import { PtyWriteUnavailableError } from '../providers/pty-write-unavailable-error'
 import { ColdRestorePayloadCache, type ColdRestorePayload } from './cold-restore-payload-cache'
 import { buildDurableCheckpointSnapshot } from './daemon-durable-history-snapshot'
+import { DAEMON_SESSION_SCROLLBACK_ROWS } from './daemon-session-scrollback-window'
 import { PtyProcessListAdmission } from '../providers/pty-process-list-admission'
 import {
   iterateTerminalHistorySeedChunks,
@@ -87,6 +88,7 @@ import {
 } from './daemon-audit-classifier'
 import type { DaemonEvidenceSource, ExactDaemonIncarnation } from './daemon-incarnation-evidence'
 import { createDaemonAuditEligibilityTracker } from './daemon-audit-eligibility-event'
+import { normalizeDesktopTerminalSnapshotRows } from '../../shared/terminal-scrollback-policy'
 
 type PendingDaemonSpawnOperation = {
   exitsBySessionId: Map<string, { incarnationId?: string }[]>
@@ -1219,9 +1221,10 @@ export class DaemonPtyAdapter implements IPtyProvider {
       return null
     }
     try {
+      const scrollbackRows = normalizeDesktopTerminalSnapshotRows(opts.scrollbackRows)
       const result = await this.client.request<GetSnapshotResult>('getSnapshot', {
         sessionId: id,
-        ...(typeof opts.scrollbackRows === 'number' ? { scrollbackRows: opts.scrollbackRows } : {})
+        ...(scrollbackRows !== undefined ? { scrollbackRows } : {})
       })
       const snapshot = result.snapshot
       // Why: older v19 daemons lack an absolute output sequence, so their snapshot can't reconcile bytes queued on the other socket.
@@ -1229,8 +1232,10 @@ export class DaemonPtyAdapter implements IPtyProvider {
         return null
       }
       const restored =
-        this.historyManager && this.historyReader && opts.scrollbackRows !== 0
-          ? await this.overlayDurableRestoreSnapshot(id, snapshot)
+        this.historyManager &&
+        this.historyReader &&
+        (scrollbackRows === undefined || scrollbackRows > DAEMON_SESSION_SCROLLBACK_ROWS)
+          ? await this.overlayDurableRestoreSnapshot(id, snapshot, scrollbackRows)
           : snapshot
       return this.toProviderBufferSnapshot(restored)
     } catch {
@@ -1268,7 +1273,8 @@ export class DaemonPtyAdapter implements IPtyProvider {
 
   private async overlayDurableRestoreSnapshot(
     sessionId: string,
-    liveSnapshot: NonNullable<GetSnapshotResult['snapshot']>
+    liveSnapshot: NonNullable<GetSnapshotResult['snapshot']>,
+    scrollbackRows?: number
   ): Promise<NonNullable<GetSnapshotResult['snapshot']>> {
     if (!this.historyManager || !this.historyReader) {
       return liveSnapshot
@@ -1291,7 +1297,8 @@ export class DaemonPtyAdapter implements IPtyProvider {
       }
       return await buildDurableCheckpointSnapshot({
         liveSnapshot,
-        restoreInfo
+        restoreInfo,
+        scrollbackRows
       })
     } catch {
       return liveSnapshot

src/main/daemon/daemon-restore-scrollback-depth.test.ts

@@ -191,6 +191,7 @@ describe('STA-4091 previously recoverable restore depth', () => {
           restoreInfo
         })
         expect(durable.outputSequence).toBe(9)
+        expect(durable.scrollbackAnsi).toBe('')
         expect(snapshotText(durable)).toContain(PREVIOUSLY_RECOVERABLE_LINE)
       } finally {
         live.dispose()
@@ -272,6 +273,23 @@ describe('STA-4091 previously recoverable restore depth', () => {
       expect(text).toContain(NEWEST_WRITTEN_LINE)
       expect(text).toContain(PREVIOUSLY_RECOVERABLE_LINE)
       expect(text).toContain(OLDEST_WRITTEN_LINE)
+      expect(text.split(OLDEST_WRITTEN_LINE)).toHaveLength(2)
+    })
+
+    it('honors a bounded remount snapshot depth', async () => {
+      const { id } = await adapter.spawn({
+        cols: 80,
+        rows: 24,
+        sessionId: 'bounded-remount-depth',
+        cwd: '/tmp'
+      })
+      lastSubprocess.emitData(numberedOutput(DESKTOP_TERMINAL_SCROLLBACK_ROWS_DEFAULT))
+
+      const snapshot = await adapter.getBufferSnapshot(id, { scrollbackRows: 24 })
+      const text = `${snapshot?.scrollbackAnsi ?? ''}${snapshot?.data ?? ''}`
+      expect(text).toContain(NEWEST_WRITTEN_LINE)
+      expect(text).not.toContain(PREVIOUSLY_RECOVERABLE_LINE)
+      expect(text).not.toContain(OLDEST_WRITTEN_LINE)
     })
 
     it('restores that depth after a keepHistory restart compact', async () => {