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Keep rotated session snapshots and hold back poorer early saves - #14824
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A relaunch that restored one empty workspace wrote it over the full layout, and a second quick relaunch copied it over -previous too (2026-09-26 incident). Now: - Launch archives the primary snapshot into Application Support/cmux/session-history/ (10 newest, plus the richest entry, which never rotates out; identical bytes are not re-archived). - An overwrite guard holds primary writes from a launch that is poorer than the snapshot it started from until it lives 5 minutes, the layout changes, or it catches up to the baseline. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Navigate logical layers of code changes, visualize relationships, and explore their blast radius. 📝 WalkthroughWalkthroughThe change adds snapshot richness and history storage to the workspace package. At startup, the app archives a loaded snapshot and installs an overwrite guard. The guard filters later snapshot writes based on richness, elapsed time, and structure. ChangesSnapshot history and overwrite protection
Priority: ⬆️ High Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant AppDelegate
participant SessionSnapshotRepository
participant SessionSnapshotOverwriteGuard
participant AppSessionSnapshot
AppDelegate->>SessionSnapshotRepository: Archive the loaded snapshot
AppDelegate->>SessionSnapshotOverwriteGuard: Install guard using baseline richness and launch date
AppDelegate->>AppSessionSnapshot: Get candidate richness and structure signature
AppDelegate->>SessionSnapshotOverwriteGuard: Evaluate candidate richness, structure, and time
SessionSnapshotOverwriteGuard-->>AppDelegate: Return write or hold decision
Suggested reviewers: Merge Risk: 🟡 Moderate · up to This change adds snapshot history and a startup guard that delays poorer saves. After a clean exit with no primary snapshot, the guard can still compare new sessions against an old backup. A new, smaller session may then not be saved, and a quick relaunch could lose it. Resolve how the baseline is chosen before merging. Security Architecture ReviewSecurity architecture risk: 🟡 Moderate · up to The change protects layouts from quick, destructive restarts, but its recovery history can preserve terminal session data after the active snapshot is removed. The identified exposure is to someone with access to the user’s stored files, not a demonstrated new remote entry point. Retained concerns
Security review detailsSecurity Blast Radius
Security Findings and Attack Paths
Trust Boundaries and Controls
Resilience and Maintainability Implications
Hardening Proposals
Important Pre-merge checks failedPlease resolve all errors before merging. Addressing warnings is optional. ❌ Failed checks (1 error, 1 inconclusive)
✅ Passed checks (23 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 24.14% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 10 files. (1 skipped: 1 too large.) Full details: Cmux Cache Substitution CorrectnessExplanation The startup snapshot path replaces fresh primary-file reads with Resolution Either retain fresh
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Inline comments:
In `@cmuxTests/SessionSnapshotOverwriteGuardAppTests.swift`:
- Around line 35-41: Update the overwrite-guard test to exercise the snapshot
save path using a temporary primary snapshot file: save the trivial snapshot,
attempt the held save, and verify the file bytes remain unchanged. After the
layout change, save the changed snapshot and verify the write is permitted.
In
`@Packages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotRepository.swift`:
- Around line 180-194: Update SessionSnapshotHistoryEntry.fileName to append a
unique identifier so snapshots archived within the same millisecond and with
equal richness do not overwrite each other. Update the corresponding history
filename parser to accept the identifier while continuing to recognize existing
filenames.
In `@Sources/AppDelegate.swift`:
- Around line 3624-3626: Update finishPreparingStartupSessionSnapshot() and the
archive, backup-sync, and restore paths to load the primary snapshot once and
pass the same SessionSnapshotLoadOutcome<AppSessionSnapshot> through them.
Preserve the .missing and .unusable outcomes so restore fallback behavior
remains unchanged.
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📒 Files selected for processing (12)
Packages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotHistoryEntry.swiftPackages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotOverwriteGuard.swiftPackages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotRepository.swiftPackages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotRepresenting.swiftPackages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotRichness.swiftPackages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotStoring.swiftPackages/macOS/CmuxWorkspaces/Tests/CmuxWorkspacesTests/Session/SessionSnapshotHistoryTests.swiftSources/AppDelegate+CrashSessionSnapshotRemoval.swiftSources/AppDelegate.swiftSources/SessionPersistence.swiftcmux.xcodeproj/project.pbxprojcmuxTests/SessionSnapshotOverwriteGuardAppTests.swift
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- A started agent (terminal agent session or resume binding) changes the structure signature, so a held launch that gains an agent writes. - When the primary is missing or unusable, archive -previous and use its richness as the baseline; startup restore falls back to it. - Install the guard on the first save if startup prep has not run yet. - Archive with copyItem (APFS clone) and compare sizes before contents. - Removals pass through without maturing the guard; fix the misplaced doc comment on sessionSnapshotStore. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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The archive, the -previous sync, and the restore each decoded the primary on the main actor. Load it once and pass the outcome through; none of the three rewrites the primary. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Actionable comments posted: 1
- 🪄 Fix CodeRabbit comments on this PR
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.
Inline comments:
In `@Sources/AppDelegate`+CrashSessionSnapshotRemoval.swift:
- Around line 63-69: Update the helper containing the candidates loop to accept
the startup recovery decision and choose its guard baseline from that decision:
use an empty baseline when startup selects a fresh session, otherwise use the
selected recovery snapshot. Keep archiving `-previous` separate from baseline
selection; do not let `sessionSnapshotStore.loadOutcome` for that backup
establish the baseline.
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📒 Files selected for processing (6)
Packages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotOverwriteGuard.swiftPackages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotRepository.swiftSources/AppDelegate+CrashSessionSnapshotRemoval.swiftSources/AppDelegate.swiftSources/SessionPersistence.swiftcmuxTests/SessionSnapshotOverwriteGuardAppTests.swift
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- Packages/macOS/CmuxWorkspaces/Sources/CmuxWorkspaces/Session/SessionSnapshotOverwriteGuard.swift
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A primary missing because the user closed every window starts fresh, so holding that session against the old -previous layout only risked losing a trivial session on a quick quit. -previous is still archived. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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4d3385b Owned-pool placement, rescue and build-state fixes (manaflow-ai#14873) b0df677 Keep rotated session snapshots and hold back poorer early saves (manaflow-ai#14824) # Conflicts: # .github/workflows/ci-macos.yml # .github/workflows/ci.yml # .github/workflows/seed-derived-data.yml
Brings in main at 6431ac2 (last green fast guards). Conflicts: - SessionSnapshotRepository.swift: main's rotated snapshot history (#14824) and this branch's SessionSnapshotFileLocation. History now derives its cmux directory and bundle-id file prefix from SessionSnapshotFileLocation (new cmuxDirectoryURL and safeBundleIdentifier), sharing the non-optional Application Support resolver with snapshot and import paths. - SessionSnapshotStoring.swift: keep both sides' protocol requirements. - project.pbxproj: union of added entries, normalized. Also fixes the newer-backup regression test's fixture: the raw string held escaped quotes, so the "newer" backup was not valid JSON and the test could not exercise preservation. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Port main's session changes into the extracted types: - #14822: SessionSnapshotPersistenceWriter writes geometry and the crash-only marker with setIfChanged/removeObjectIfPresent. - #14824: persistSessionSnapshot installs and consults the snapshot overwrite guard before handing the snapshot to the writer. - #14861: the test probe store implements the new SessionSnapshotStoring import/export/history requirements. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
…ly saves Ported from upstream manaflow-ai#14824 (b0df677): "Keep rotated session snapshots and hold back poorer early saves (manaflow-ai#14824)". Conflict notes: the fork's SessionSnapshotRepository has no decoderUserInfo, so only historyLimit was added; the AppDelegate guard property sits without the todo-state coordinator.
…muxTests group children The manaflow-ai#14824 port inserted the group child after the list's closing paren, which left project.pbxproj unparseable.
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On 2026-09-26 the stable app died with five agent sessions open. The relaunch restored one empty workspace and saved it over
session-com.cmuxterm.app.json; a second quick relaunch copied that over-previous.json. The only full layout left was a day old (manaflow-ai/cmuxterm-hq#760).After this change two quick restarts can't wipe the layout:
-previouswhen the primary is missing or unusable) intoApplication Support/cmux/session-history/session-<bundle>-<unix ms>-w<workspaces>-p<panels>.json. It keeps the 10 newest entries plus the richest one, so a run of trivial launches can't rotate the last full layout out. Identical bytes aren't archived twice. Richness sits in the file name, so listing and pruning never decode JSON.-previouswhen the primary is unusable or missing after an unclean exit. A primary missing because the user closed every window starts fresh with no baseline. A launch whose snapshot is poorer than that doesn't write the primary file until one of these happens: the session lives 5 minutes, the workspace/panel identities or a terminal's agent session change after the first save (the user changed the layout or started an agent), or it catches up to the baseline. Until then a crash or quick relaunch restores the richer snapshot. Geometry still saves. The guard is off under XCTest.To recover by hand, quit cmux and copy a history file over
session-<bundle>.json. Item 2 of the incident follow-up (journal-based agent recovery andcmux session restore) comes in a separate PR.Testing
swift test --filter SessionSnapshotinPackages/macOS/CmuxWorkspaces: 19 tests passed, 7 of them new.cmuxTests/SessionSnapshotOverwriteGuardAppTests.swiftruns the app path throughAppDelegate: a realTabManagersnapshot is held, then released once a workspace is added or an agent session appears in a held panel. It runs in CI.python3 scripts/verify-local.py --affected upstream/main --swift-changed upstream/main: 5/5 passed.🤖 Generated with Claude Code
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@codesmith-botwith what you need. Autofix is disabled.Summary by cubic
Fixes the incident where a relaunch restoring an empty session overwrote the full layout, and a second quick relaunch copied that empty layout onto the backup file.
History
-previousbackup when the primary is missing or unusable) toApplication Support/cmux/session-history/before any restore or save.-previoussync, and the restore.Overwrite guard
-previouswhen startup recovers it; a primary missing because the user closed every window starts fresh with no baseline (-previousis still archived).session-<bundle>.json.Written for commit 6633a17. Summary will update on new commits.
Summary by CodeRabbit