fix(ios): one owner of the engine lifecycle — claimed background stops, no restart without ownership, followers mirror the leader (#183) - #190
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…s, no restart without ownership, followers mirror the leader (#183) Foreground scene and background runs share one process-global engine, and ownership was a bare flag. Background handlers read it and then stopped the engine outside any lock, so a foreground adoption landing in between attached to an engine about to die. After the scene released the flag on backgrounding, the manager kept polling and treated a background handler's own stop as a death, restarting an engine it no longer owned. And a coalesced second background run answered .alreadyIdle on its own, so a failed leader run still read as success. SyncLifecycleState is now the one place ownership changes: a background stop is claimed under the lock and runs outside it (stopEngineIfBackgroundOwned, used by every stop path: cleanup, both BGTask expiration handlers, continued processing, the forced silent-push restart); adoption is refused while a stop claim holds and a cold start waits for it to clear before touching the bridge; the manager heals a dead engine only while the foreground owns the lifecycle and otherwise detaches quietly; the single-flight follower waits for the leader and reports the leader's result (BackgroundSyncSingleFlight). What could go wrong and why this is safe: a claim that never clears would hold the foreground start forever, and a follower that never wakes would keep a BGTask past its budget. The start wait is bounded by the bridge's own stop deadline and proceeds afterwards (the bridge serializes the start behind the stop); a follower cancelled while waiting resumes with no result and reports failure, and a follower admitted on an already-cancelled task never waits. Each window is reproduced RED against real engines on main first (four tests), the claim machine and the admission are pinned without an engine, and the full Xcode plan passes. Decision 040 records the invariants. Closes #183
📝 WalkthroughWalkthroughThe change coordinates foreground and background ownership of the Syncthing engine. Background stops use lifecycle claims, foreground starts and adoption honor those claims, and concurrent background runs return the leader’s result. Tests and architecture records cover the new rules. ChangesLifecycle ownership coordination
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Bug fix · Severity of issue fixed: Medium Merge Risk: 🟠 High · up to Concurrent background and foreground activity can abort synchronization or prevent the app from starting its engine correctly. These lifecycle defects should be fixed before merge. 🚥 Pre-merge checks | ✅ 7✅ Passed checks (7 passed)
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Actionable comments posted: 4
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Inline comments:
In `@ios/VaultSync/Services/BackgroundSyncService.swift`:
- Around line 116-118: Update beginBackgroundStop() to reject or join an
existing backgroundStopInProgress claim instead of returning success for a
second stop, while keeping that result distinct from refusal due to
foregroundActive. Ensure endBackgroundStop() cannot clear the shared claim while
another stop operation remains active, preventing foreground start or adoption
from using an engine that is still stopping.
- Line 1151: Update the expiration handlers near stopEngineIfBackgroundOwned so
only the single-flight leader may stop the shared engine; follower expiration
must cancel only its own task and report failure. Use the existing
leader/follower state or ownership marker in the background sync flow to gate
stopEngineIfBackgroundOwned, preserving leader cleanup behavior.
- Around line 1987-2016: Update forceRestartForSilentPush and its
lifecycle-claim handling so the background ownership claim remains valid across
stopping, the 350 ms wait, and startSyncthing. Prevent SyncthingManager.start or
adoptRunningEngine from taking foreground ownership during this sequence, and
validate ownership atomically before starting; return foregroundOwns or failed
rather than starting or reporting restarted when the foreground owns the engine.
In `@ios/VaultSync/Services/SyncthingManager.swift`:
- Around line 696-711: Update the startup flow around claimForegroundForStart,
waitForBackgroundStopToClear, and startSyncthing so a timeout does not proceed
with foreground startup while a background stop remains active. Abort or defer
the operation when stopCleared is false, and invoke startSyncthing only after
the stop claim has cleared.
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📒 Files selected for processing (11)
CHANGELOG.mddocs/architecture.mddocs/decisions/040-one-owner-of-the-engine-lifecycle.mdios/VaultSync/Services/BackgroundSyncService.swiftios/VaultSync/Services/BackgroundSyncSingleFlight.swiftios/VaultSync/Services/SyncthingManager.swiftios/VaultSyncTests/EngineDeathDetectionTests.swiftios/VaultSyncTests/LifecycleOwnershipCoreTests.swiftios/VaultSyncTests/LifecycleOwnershipTests.swiftios/VaultSyncTests/OnboardingEngineAttachTests.swiftios/VaultSyncTests/SceneActivationAdoptionTests.swift
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📓 Path-based instructions (14)
Focus on Swift 6 strict concurrency, Sendable/MainActor correctness, Task cancellation, retain cycles, memory pressure, SwiftUI observation state, StoreKit/APNs flows, and iOS background execution limits.
⚙️ CodeRabbit configuration file
Files:
ios/VaultSyncTests/EngineDeathDetectionTests.swiftios/VaultSyncTests/LifecycleOwnershipTests.swiftios/VaultSyncTests/LifecycleOwnershipCoreTests.swiftios/VaultSyncTests/SceneActivationAdoptionTests.swiftios/VaultSyncTests/OnboardingEngineAttachTests.swiftios/VaultSync/Services/BackgroundSyncSingleFlight.swiftios/VaultSync/Services/SyncthingManager.swiftios/VaultSync/Services/BackgroundSyncService.swift
Review public documentation for technical accuracy, privacy/security claims, App Store-facing wording, setup correctness, and consistency with the free app plus optional Cloud Relay subscription model.
⚙️ CodeRabbit configuration file
Files:
CHANGELOG.mddocs/decisions/040-one-owner-of-the-engine-lifecycle.mddocs/architecture.md
VaultSync syncs private Obsidian notes through Syncthing.
⚙️ CodeRabbit configuration file
Files:
ios/VaultSyncTests/EngineDeathDetectionTests.swiftios/VaultSyncTests/LifecycleOwnershipTests.swiftios/VaultSyncTests/LifecycleOwnershipCoreTests.swiftios/VaultSyncTests/SceneActivationAdoptionTests.swiftios/VaultSyncTests/OnboardingEngineAttachTests.swiftCHANGELOG.mddocs/decisions/040-one-owner-of-the-engine-lifecycle.mdios/VaultSync/Services/BackgroundSyncSingleFlight.swiftios/VaultSync/Services/SyncthingManager.swiftdocs/architecture.mdios/VaultSync/Services/BackgroundSyncService.swift
Diagnostics publication, registry digests, rollout state, and public artifact availability must be established only by the owner-gated workflow and evidence in `helper-publication-rollout.md`; source text must never claim publication.
📄 CodeRabbit inference engine (docs/helper-runtime-packaging-readiness.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.mddocs/architecture.md
Revocation and rollback must preserve immutable authorization history and all retained Syncthing peer, versioning, backup, conflict, remote-history, and tombstone copies; rollback or downgrade must not erase, rewrite, replace, regenerate, o...
📄 CodeRabbit inference engine (docs/helper-runtime-packaging-readiness.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.mddocs/architecture.md
a relay rate-limit (HTTP 429) counts as **success** — it proves the trigger endpoint is reachable An inactive subscription prints a `WARN` for the trigger check (`WARN Relay trigger endpoint response sanity`, followed by `relay reports no a...
📄 CodeRabbit inference engine (docs/troubleshooting.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.mddocs/architecture.md
Diagnostics is additive and opt-in: without both explicit configuration paths, helper 2.0.2 must retain prior Trigger-v1 behavior and create no diagnostics state.
📄 CodeRabbit inference engine (docs/helper-publication-rollout.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.mddocs/architecture.md
Do not log or persist private/public keys, secrets, QR payloads, TLS pins, identifiers or digests, bindings, nonces, transcript fingerprints, signed bodies, paths, or credential records; update `PRIVACY.md` before runtime credential transpo...
📄 CodeRabbit inference engine (docs/decisions/022-diagnostics-helper-credentials-and-mutual-pairing.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.md
Classify a connected root as a container, never as a vault-as-root, when it contains at least one direct subdirectory containing `.obsidian/`, regardless of whether the root itself contains `.obsidian/`.
📄 CodeRabbit inference engine (docs/decisions/014-vault-subfolders-override-stray-root-config.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.md
Every Relay provision request must require a locally verified, active Relay entitlement and its signed StoreKit transaction; never send a placeholder when this evidence is unavailable.
📄 CodeRabbit inference engine (docs/decisions/018-relay-reprovision-requires-verified-entitlement.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.md
Keep background start, local data progress, upload, download, and full-roundtrip proof as independent fields; never derive a global success flag.
📄 CodeRabbit inference engine (docs/decisions/020-sync-path-proof-requires-correlated-evidence.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.md
Keep the diagnostics capability disabled until human security and product approval, separate pairing/canonical-contract decisions, and required implementation evidence are complete.
📄 CodeRabbit inference engine (docs/decisions/023-diagnostics-namespace-and-least-privilege-access.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.md
Treat Decisions 022–024 as formally proposed designs whose text and status remain unchanged by this approval record.
📄 CodeRabbit inference engine (docs/decisions/025-owner-approval-of-diagnostics-design-gates.md)
Files:
docs/decisions/040-one-owner-of-the-engine-lifecycle.md
For Swift background execution changes, pass if work is bounded, cancellation-aware, handles expiration callbacks, and records errors without leaking private vault data.
📄 CodeRabbit inference engine (Custom checks)
Files:
ios/VaultSyncTests/EngineDeathDetectionTests.swiftios/VaultSyncTests/LifecycleOwnershipTests.swiftios/VaultSyncTests/LifecycleOwnershipCoreTests.swiftios/VaultSyncTests/SceneActivationAdoptionTests.swiftios/VaultSyncTests/OnboardingEngineAttachTests.swiftios/VaultSync/Services/BackgroundSyncSingleFlight.swiftios/VaultSync/Services/SyncthingManager.swiftios/VaultSync/Services/BackgroundSyncService.swift
🧠 Learnings (1)
📓 Common learnings
Learnt from: CR
Repo: psimaker/vaultsync
Timestamp: 2026-09-15T11:12:39.373Z
Learning: A background stop is claimed under the lock (`beginBackgroundStop`, refused while the foreground owns), runs outside it, then releases the claim
Learnt from: CR
Repo: psimaker/vaultsync
Timestamp: 2026-09-15T11:12:39.373Z
Learning: `SyncLifecycleState` is the one place ownership changes, through its methods only.
Learnt from: CR
Repo: psimaker/vaultsync
Timestamp: 2026-09-15T11:12:39.373Z
Learning: every background stop path goes through `stopEngineIfBackgroundOwned`.
Learnt from: CR
Repo: psimaker/vaultsync
Timestamp: 2026-09-15T11:12:39.373Z
Learning: A single-flight follower waits for the leader and reports the leader's result; a follower cancelled while waiting reports failure.
Learnt from: CR
Repo: psimaker/vaultsync
Timestamp: 2026-09-15T11:12:39.373Z
Learning: Foreground adoption is refused while a stop claim holds, and a cold start waits for the claim to clear before it touches the bridge.
Learnt from: CR
Repo: psimaker/vaultsync
Timestamp: 2026-09-15T11:12:39.373Z
Learning: The manager heals a dead engine (decision 009) only while it owns the lifecycle; without ownership it detaches quietly and the next scene activation attaches again.
🔇 Additional comments (5)
ios/VaultSync/Services/BackgroundSyncSingleFlight.swift (1)
1-90: LGTM!ios/VaultSync/Services/SyncthingManager.swift (1)
696-704: LGTM!Also applies to: 711-711, 745-758, 763-763, 845-845, 1051-1051, 1081-1092
ios/VaultSyncTests/LifecycleOwnershipTests.swift (1)
1-148: LGTM!ios/VaultSyncTests/OnboardingEngineAttachTests.swift (1)
29-29: LGTM!Also applies to: 50-50, 77-77, 106-106
CHANGELOG.md (1)
20-20: LGTM!
10 tasks
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Closes #183 (child of #151). Branches from
mainafter #181; independent of #189.What
SyncLifecycleStateis the one place engine ownership changes (methods only,private(set)flags):claimForegroundForStart,claimForegroundForAdoption(refused while a background stop claim holds),releaseForeground,beginBackgroundStop(refused while the foreground owns),endBackgroundStop.stopEngineIfBackgroundOwned(context:): claim under the lock, stop outside it, release — used by cleanup, both BGTask expiration handlers, continued-processing termination and the forced silent-push restart (which now reportsforegroundOwnsinstead of pretending a restart).SyncthingManager.start()claims first and waits (bounded, 35 s) for an in-flight background stop to clear;adoptRunningEngine()refuses during a stop;handleEngineDeathdetaches without restart when the foreground does not own the lifecycle.BackgroundSyncSingleFlight: a follower waits for the leader and reports the leader's result; cancelled followers report failure; no double resume.Reproduction (RED on
main, real engines)LifecycleOwnershipTests(4 tests, 9 failed expectations onmain): detached manager restarted the engine; adoption succeeded during a stop claim;start()ran into a stop claim; follower answered.alreadyIdlewhile the leader ended with.noFoldersConfigured.Verification
go/— see checklist below.Summary
SyncLifecycleState.Verification