From adf85f0f225604cb1e13141ca709ce814661c105 Mon Sep 17 00:00:00 2001
From: Brennan Benson <79079362+brennanb2025@users.noreply.github.com>
Date: Thu, 13 Aug 2026 04:15:01 -0700
Subject: [PATCH] fix(terminal): retain live history after restore loss

---
 src/main/daemon/daemon-pty-adapter.ts         | 19 ++++++---
 .../daemon-restore-scrollback-depth.test.ts   | 39 +++++++++++++++++++
 2 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/src/main/daemon/daemon-pty-adapter.ts b/src/main/daemon/daemon-pty-adapter.ts
index 20af546e06c..d605afd3a59 100644
--- a/src/main/daemon/daemon-pty-adapter.ts
+++ b/src/main/daemon/daemon-pty-adapter.ts
@@ -2217,9 +2217,12 @@ export class DaemonPtyAdapter implements IPtyProvider {
               sessionId,
               take.snapshot,
               [...take.drainedRecords, ...take.records],
-              opts.requireContinuityProof === true
-                ? { requiredPreviousPendingOutputSeq: take.seq - 1 }
-                : undefined
+              {
+                pendingRecordsAreComplete: take.seq === 1,
+                ...(opts.requireContinuityProof === true
+                  ? { requiredPreviousPendingOutputSeq: take.seq - 1 }
+                  : {})
+              }
             )
       const checkpoint = await this.historyManager.checkpoint(sessionId, snapshot, {
         pendingOutputSeq: take.seq
@@ -2259,7 +2262,10 @@ export class DaemonPtyAdapter implements IPtyProvider {
     sessionId: string,
     liveSnapshot: NonNullable<TakePendingOutputResult['snapshot']>,
     pendingRecords: TakePendingOutputResult['records'],
-    opts?: { requiredPreviousPendingOutputSeq?: number }
+    opts: {
+      pendingRecordsAreComplete: boolean
+      requiredPreviousPendingOutputSeq?: number
+    }
   ): Promise<NonNullable<TakePendingOutputResult['snapshot']>> {
     if (!this.historyReader) {
       return liveSnapshot
@@ -2270,8 +2276,9 @@ export class DaemonPtyAdapter implements IPtyProvider {
         wslDistro: this.wslDistrosBySessionId.get(sessionId)
       })
       if (
-        opts?.requiredPreviousPendingOutputSeq !== undefined &&
-        restoreInfo?.pendingOutputSeq !== opts.requiredPreviousPendingOutputSeq
+        (!restoreInfo && !opts.pendingRecordsAreComplete) ||
+        (opts.requiredPreviousPendingOutputSeq !== undefined &&
+          restoreInfo?.pendingOutputSeq !== opts.requiredPreviousPendingOutputSeq)
       ) {
         console.warn('[history] durable continuity unproven; using live snapshot:', sessionId)
         return liveSnapshot
diff --git a/src/main/daemon/daemon-restore-scrollback-depth.test.ts b/src/main/daemon/daemon-restore-scrollback-depth.test.ts
index ad1d4300eaf..3cc1d5d7ce2 100644
--- a/src/main/daemon/daemon-restore-scrollback-depth.test.ts
+++ b/src/main/daemon/daemon-restore-scrollback-depth.test.ts
@@ -8,6 +8,7 @@ import { DaemonServer } from './daemon-server'
 import { buildDurableCheckpointSnapshot } from './daemon-durable-history-snapshot'
 import { DAEMON_RESTORE_SCROLLBACK_ROWS } from './daemon-restore-scrollback-depth'
 import { DAEMON_SESSION_SCROLLBACK_ROWS } from './daemon-session-scrollback-window'
+import { getHistorySessionDirName } from './history-paths'
 import { getDaemonSocketPath } from './daemon-spawner'
 import { HeadlessEmulator } from './headless-emulator'
 import { HistoryManager } from './history-manager'
@@ -372,6 +373,44 @@ describe('STA-4091 previously recoverable restore depth', () => {
       expect(snapshotText(restore ?? {})).toContain(OLDEST_WRITTEN_LINE)
     })
 
+    it('uses the live window when durable history disappears after a prior drain', async () => {
+      const { id } = await adapter.spawn({
+        cols: 80,
+        rows: 24,
+        sessionId: 'missing-history-after-drain',
+        cwd: '/tmp'
+      })
+      lastSubprocess.emitData(numberedOutput(DESKTOP_TERMINAL_SCROLLBACK_ROWS_DEFAULT))
+      await adapter.getBufferSnapshot(id)
+      lastSubprocess.emitData(`${FRESH_AFTER_CHECKPOINT}\r\n`)
+
+      const internals = adapter as unknown as { checkpointDirtySessions: () => Promise<void> }
+      await internals.checkpointDirtySessions()
+      rmSync(join(historyDir, getHistorySessionDirName(id), 'checkpoint.json'))
+      lastSubprocess.emitData('TAIL_AFTER_HISTORY_LOSS\r\n')
+      const warn = vi.spyOn(console, 'warn').mockImplementation(() => {})
+
+      try {
+        const snapshot = await adapter.getBufferSnapshot(id)
+        const text = `${snapshot?.scrollbackAnsi ?? ''}${snapshot?.data ?? ''}`
+        expect(text).toContain(NEWEST_WRITTEN_LINE)
+        expect(text).toContain('TAIL_AFTER_HISTORY_LOSS')
+        expect(text).not.toContain(OLDEST_WRITTEN_LINE)
+        const restored = await new HistoryReader(historyDir).detectColdRestore(id, {
+          ignoreCleanEnd: true
+        })
+        expect(snapshotText(restored ?? {})).toContain(NEWEST_WRITTEN_LINE)
+        expect(snapshotText(restored ?? {})).toContain('TAIL_AFTER_HISTORY_LOSS')
+        expect(restored?.scrollbackLines).toBe(DAEMON_SESSION_SCROLLBACK_ROWS)
+        expect(warn).toHaveBeenCalledWith(
+          '[history] durable continuity unproven; using live snapshot:',
+          id
+        )
+      } finally {
+        warn.mockRestore()
+      }
+    })
+
     it('preserves durable depth after an incremental append and adapter crash', async () => {
       const { id } = await adapter.spawn({
         cols: 80,