diff --git a/src/main/daemon/daemon-pty-adapter.ts b/src/main/daemon/daemon-pty-adapter.ts
index cd73232acf7..7a962caff9c 100644
--- a/src/main/daemon/daemon-pty-adapter.ts
+++ b/src/main/daemon/daemon-pty-adapter.ts
@@ -186,6 +186,21 @@ export class DaemonPtyAdapter implements IPtyProvider {
     }
 
     if (this.historyManager && result.isNew) {
+      // Why (design doc §9 post-release monitoring): a spawn with an explicit
+      // sessionId that produced a brand-new daemon session AND has no disk
+      // history is the signal that either (a) the reaper ate a dir the user
+      // still wanted, or (b) the persisted mapping pointed at a session that
+      // never wrote a checkpoint. This shouldn't happen under the defensive
+      // keep-set derivation — if it starts showing up in logs, investigate
+      // before the next release.
+      if (opts.sessionId !== undefined && !restoreInfo) {
+        console.warn('[pty] cold-restore miss for explicit sessionId — no disk history found', {
+          sessionId,
+          worktreeId: opts.worktreeId,
+          tabId: opts.tabId,
+          leafId: opts.leafId
+        })
+      }
       void this.historyManager
         .openSession(sessionId, {
           cwd: effectiveCwd ?? '',
diff --git a/src/main/index.ts b/src/main/index.ts
index d351fa2395e..fa8d9d824cb 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -550,12 +550,18 @@ app.whenReady().then(async () => {
         liveDaemonSessionIds.add(id)
       }
     }
-    await runOrphanHistoryReaper({
+    const reapStats = await runOrphanHistoryReaper({
       historyBasePath: getHistoryDir(),
       sidecarDir: app.getPath('userData'),
       workspaceSession: store.getWorkspaceSession(),
       liveDaemonSessionIds
     })
+    // Why (design doc §9): log counts so post-release we can tell whether
+    // the reaper is firing at all and whether the three gates (keep set,
+    // mtime grace, quarantine) are in their expected ratios. Persistent
+    // non-zero `reaped` without corresponding shrinkage of history dirs in
+    // the wild would indicate a logic bug worth investigating.
+    console.log('[history-reaper] startup pass stats:', reapStats)
   } catch (error) {
     console.warn('[history-reaper] startup pass failed:', error)
   }
diff --git a/tests/e2e/terminal-restart-persistence.spec.ts b/tests/e2e/terminal-restart-persistence.spec.ts
index 87da9ab28d2..d85d9b0ca12 100644
--- a/tests/e2e/terminal-restart-persistence.spec.ts
+++ b/tests/e2e/terminal-restart-persistence.spec.ts
@@ -27,7 +27,8 @@
  *     removed periodic save represented.
  */
 
-import { readFileSync, existsSync } from 'fs'
+import { readFileSync, writeFileSync, existsSync } from 'fs'
+import { join } from 'path'
 import type { ElectronApplication, Page } from '@stablyai/playwright-test'
 import { test, expect } from './helpers/orca-app'
 import { TEST_REPO_PATH_FILE } from './global-setup'
@@ -227,6 +228,83 @@ test.describe('Terminal restart persistence', () => {
     }
   })
 
+  test('scrollback survives quit with missing ptyId (Issue #217 regression)', async (// oxlint-disable-next-line no-empty-pattern -- Playwright's second fixture arg is testInfo; the first must be an object destructure to opt out of the default fixture set.
+  {}, testInfo) => {
+    // Why (design doc §7.2): this is the load-bearing test for the
+    // deterministic-sessionId fix. Issue #217 failed specifically when
+    // orca-data.json's `ptyId` field was empty at restore time (the
+    // SIGKILL-between-spawn-and-persist window). Before the fix, the
+    // renderer had no way to reach the on-disk history dir without that
+    // field. After the fix, mintPtySessionId(worktreeId, tabId, leafId)
+    // reproduces the same id, so the cold-restore reader finds the dir
+    // anyway. We simulate the race here by mutating the persisted
+    // orca-data.json between launches — deleting the ptyId field gives
+    // us the exact state the old code couldn't recover from, without
+    // the flakiness of racing a real SIGKILL.
+    const repoPath = readFileSync(TEST_REPO_PATH_FILE, 'utf-8').trim()
+    if (!repoPath || !existsSync(repoPath)) {
+      test.skip(true, 'Global setup did not produce a seeded test repo')
+      return
+    }
+
+    const session = createRestartSession(testInfo)
+    let firstApp: ElectronApplication | null = null
+    let secondApp: ElectronApplication | null = null
+
+    try {
+      // ── First launch: produce scrollback, let clean quit flush state ──
+      const firstLaunch = await session.launch()
+      firstApp = firstLaunch.app
+      const { worktreeId, ptyId } = await bootstrapFirstLaunch(firstLaunch.page, repoPath)
+
+      const marker = `DETERMINISTIC_RESTORE_${Date.now()}`
+      await execInTerminal(firstLaunch.page, ptyId, `echo ${marker}`)
+      await waitForTerminalOutput(firstLaunch.page, marker)
+
+      await session.close(firstApp)
+      firstApp = null
+
+      // Simulate the SIGKILL-before-persist race: strip ptyId from every
+      // tab in the persisted session. The terminal-history/ dir stays on
+      // disk (it was written by the daemon's checkpoint tick, not by
+      // orca-data.json). Pre-fix code would fail to find it; post-fix
+      // code re-derives the id from (worktreeId, tabId, leafId) and
+      // hits the same directory.
+      const dataFile = join(session.userDataDir, 'orca-data.json')
+      const data = JSON.parse(readFileSync(dataFile, 'utf-8')) as {
+        workspaceSession?: {
+          tabsByWorktree?: Record<string, { ptyId: string | null }[]>
+        }
+      }
+      const tabs = data.workspaceSession?.tabsByWorktree?.[worktreeId] ?? []
+      for (const tab of tabs) {
+        tab.ptyId = null
+      }
+      writeFileSync(dataFile, JSON.stringify(data))
+
+      // ── Second launch: deterministic path must recover scrollback ────
+      const secondLaunch = await session.launch()
+      secondApp = secondLaunch.app
+      await bootstrapRestoredLaunch(secondLaunch.page, worktreeId)
+
+      await expect
+        .poll(async () => (await getTerminalContent(secondLaunch.page)).includes(marker), {
+          timeout: 15_000,
+          message:
+            'Deterministic-sessionId restore did not recover scrollback when ptyId was missing'
+        })
+        .toBe(true)
+    } finally {
+      if (secondApp) {
+        await session.close(secondApp)
+      }
+      if (firstApp) {
+        await session.close(firstApp)
+      }
+      session.dispose()
+    }
+  })
+
   test('idle session does not spam session.set writes', async (// oxlint-disable-next-line no-empty-pattern -- Playwright's second fixture arg is testInfo; the first must be an object destructure to opt out of the default fixture set.
   {}, testInfo) => {
     const repoPath = readFileSync(TEST_REPO_PATH_FILE, 'utf-8').trim()