fix(shared): checkpoint WAL without blocking foreground writes

[JustYannicc]

Problem

A commit can trip the writer's 10,000-frame WAL backstop and checkpoint on the main thread even while the background worker is running. This is the failure confirmed in #20203. A synthetic adapter fixture with about 16,000 pending frames stalled a small delete for 5.48 seconds.

Change

Let the worker checkpoint and pause new writes when it falls behind. Before truncating, the worker waits for the writer to acknowledge its pause. Admission is checked again immediately before synchronous SQL runs, and generation checks reject stale worker snapshots.

Statements hold their selected connection permit across admission and execution. Cancellation transfers an elected wake to the next waiter and releases acquired permits. Waits preserve the caller's cancellation mask, so ordinary requests can cancel while masked cleanup completes. Reads and active transactions can finish while new writes wait. Mutating pragmas and partially committed statement failures participate in accounting.

The 10,000-frame threshold controls admission between statements and transactions; one operation can cross it. An external reader can keep new writes waiting until its snapshot ends. Unsupported SQLite versions and worker failure retain the existing writer-checkpoint fallback. Durability settings are unchanged.

Scope and approval

Fixes #20203. The linked maintainer comment establishes the main-thread checkpoint failure. This is one backend checkpoint fix in the existing adapter and its tests; connection ownership and cancellation changes keep asynchronous write admission safe. No UI or public API changes.

Verification

• On upstream base 16918b57d6754d6f145e9b6367c825aa31a740da, vp test run packages/shared/src/nodeSqliteClient.test.ts --maxWorkers=1: 51 passed; one pre-existing local large-blob binding failure returned null instead of 65537. That assertion also fails on the unchanged base in this macOS environment. Its precise local cause is unisolated; no assertion was weakened or skipped.
• Targeted formatting and lint, plus the shared-package typecheck, pass.
• Regression fixtures cover acknowledged truncation, scheduler progress, final admission, stale worker replies, read routing, transaction completion, raw reserved connections, cancellation before and after wake, permit grant, masked cleanup, partial writes, mutating pragmas and worker failure.
• The initial checkpoint patch carried by Signalbox #1000 passed every hosted check. Upstream head 05a3d3a872 passed CI. Current head 7e69ce7d03 additionally answers checks received while truncation is pending, preserving the pending generation so stale snapshots stay rejected. Its deterministic regression fails before the fix and passes after it. vp test run packages/shared/src/nodeSqliteClient.test.ts --maxWorkers=2: 52 passed, with only the same documented local large-blob failure. Scoped lint, formatting, shared-package typecheck and diff checks pass; hosted checks for the new head are pending.

Live desktop performance remains unverified. The known fallback can still checkpoint on the writer when a worker is unavailable.

Independent review: GPT 6.1 Sol xhigh (Opus unavailable: rate-limited at 2026-10-17 15:47:05 UTC). The exact patch passed standards and input review; upstream applicability review also found no issues on 05a3d3a8721824f6e3910a1e628b519078cce385.

Implemented with GPT 6.0 Luna max and GPT 6.1 Sol through the Codex harness in T3 Code.

[macroscopeapp]

Approvability

Verdict: Needs Human Approval

Macroscope's review found this PR requires human approval — This PR makes a substantial production change to SQLite WAL checkpointing, writer admission, transaction ownership, and cancellation behavior, including automatically delaying writes at a WAL threshold. Its concurrency complexity and changed operational defaults warrant human review despite extensive regression tests.

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• packages/shared/src/nodeSqliteClient.test.ts
• packages/shared/src/nodeSqliteClient.ts

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📝 Walkthrough

The SQLite client replaces periodic worker checkpoints and writer auto-checkpointing with WAL monitoring, coordinated truncation, and admission control for classified writes. It also updates transaction acquisition and cleanup to track interruption restoration. Tests cover checkpoint progress, blocked writers, cancellation, partial writes, and worker failure.

Changes: SQLite WAL checkpoint coordination

Layer / File(s)	Summary
WAL monitoring and coordinated truncation packages/shared/src/nodeSqliteClient.ts, packages/shared/src/nodeSqliteClient.test.ts	The worker monitors WAL frames and file size, and coordinates checkpoint and truncation requests with the main thread. Tests cover checkpoint progress, reader-blocked truncation, worker synchronization, and worker failure.
Statement classification and write admission packages/shared/src/nodeSqliteClient.ts, packages/shared/src/nodeSqliteClient.test.ts	The client uses the SQLite authorizer to classify statements and gates writes when checkpoint state requires it. Tests cover queued writes, cancellation, scheduler dispatch, incremental vacuum, partial writes, and WAL limits.
Transaction acquisition and interruption handling packages/shared/src/nodeSqliteClient.ts, packages/shared/src/nodeSqliteClient.test.ts	Transaction acquisition tracks interruptibility restoration through setup and cleanup. Borrowed operations run under the selected connection lock. Tests cover interruption, cancellation, and permit release.

Priority: ⬆️ High

Estimated code review effort: 4 (Complex) | ~60 minutes

Change: Bug fix · Severity of issue fixed: High

Suggested reviewers: t3dotgg

Merge Risk: 🔵 Low · up to 7e69c

This change alters when database writes are held during WAL checkpointing. The reported fix for a possible write hang is covered by a regression test, and no outstanding defect was found. Live desktop behavior has not been verified. Mergeable, but the author should confirm behavior under real disk load.

Security architecture risk: 🔵 Low · up to 7e69c

The change stays within the existing database and worker arrangement. The reviewed paths include safeguards for stale checkpoint state, cancellation, and worker failure. Long-lived database readers can delay new writes, but no introduced security defect was established.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The demonstrated availability scope is new writes sharing the adapter's writer and database file. A reader snapshot can hold those writes behind truncation while the separate reader path continues. The evidence does not establish remote attacker control over such snapshots or a tenant-to-database mapping.

Trust Boundaries and Controls

• observed — The worker executes a fixed internal source string and receives the database filename through workerData. The routed callback only observes replies in tests; it does not establish a new attacker-controlled message channel.

Resilience and Maintainability Implications

• observed — Tests exercise stale checkpoint snapshots, interrupted transaction and reserved-connection acquisition, reader-held truncation, and worker termination. They assert subsequent progress or visible row state, providing counterevidence to stranded ownership and premature admission; these tests were inspected, not executed.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly and concisely describes the primary change: moving WAL checkpointing off the foreground write path.
Description check		The description covers the problem, implementation, scope and approval, verification results, known limitations, and agent attribution. It links the related issue and reports the documented pre-existi…
Linked Issues check		Issue #20203 requires the server to continue answering requests during automatic history maintenance. The PR moves supported WAL checkpoint and truncation work to the worker, pauses new writes at the …
Out of Scope Changes check		The changes remain in the shared SQLite adapter and its tests. Connection permits, cancellation handling, transaction cleanup, statement accounting, mutating pragma accounting, and worker-failure fall…

Full details: Description check

Explanation

The description covers the problem, implementation, scope and approval, verification results, known limitations, and agent attribution. It links the related issue and reports the documented pre-existing test failure and pending hosted checks.

Full details: Linked Issues check

Explanation

Issue #20203 requires the server to continue answering requests during automatic history maintenance. The PR moves supported WAL checkpoint and truncation work to the worker, pauses new writes at the 10,000-frame threshold, waits for writer acknowledgement, and rechecks admission before synchronous SQL. Reads and active transactions can complete while new writes wait. The current-head change preserves the pending truncate generation and returns a blocked checkpoint reply for checks received during truncation. The added regression test covers that stale-snapshot case. The PR documents the existing writer-checkpoint fallback when worker support is unavailable. Live desktop performance is not a coding requirement for this issue.

Full details: Out of Scope Changes check

Explanation

The changes remain in the shared SQLite adapter and its tests. Connection permits, cancellation handling, transaction cleanup, statement accounting, mutating pragma accounting, and worker-failure fallback support safe checkpoint coordination and write admission. The current-head change only handles worker checks received during pending truncation. No UI, public API, or unrelated product changes are shown.

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Actionable comments posted: 1

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🤖 Prompt to fix review comments

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Inline comments:
Review comments at @packages/shared/src/nodeSqliteClient.ts:
- Around line 632-635: Update the `pendingTruncate` branch to reply to incoming
`check` requests with the pending checkpoint state, including the request ID and
pending generation, and mark the reply as blocked. Preserve barrier counting and
the existing return behavior so the main thread clears its in-flight check
without applying a stale snapshot.

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• packages/shared/src/nodeSqliteClient.test.ts
• packages/shared/src/nodeSqliteClient.ts

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[juliusmarminge]

Taking over this one for batch misc-03. I am rebuilding it on current main as two reviewable layers: connection ownership/cancellation, then the complete WAL checkpoint/admission protocol. I will preserve credit and compare the replacement against this full diff before closing this PR. Nothing will be merged by this batch.

[juliusmarminge]

Thanks @JustYannicc — the worker checkpoint coordination, bounded-WAL investigation, cancellation cases, and pending-truncate reply fix supplied the basis for this takeover.

I rebuilt it from main as two focused layers:

• #21798: connection ownership and interruptible acquisition, independently retaining the old WAL backstop.
• #21799: the complete background checkpoint/admission protocol, fallback, and real SQLite concurrency coverage.

I compared the entire original SQLite source/test diff at the initial head and checked the later main merge; that merge changes neither SQLite file. Connection ownership landed in the bottom layer, while mutation classification, transaction completion, cancellation, generation/truncate handshakes, pending-check replies, size limits and worker fallback landed in the top. Repeated fixtures and redundant wrapper/state machinery were removed. No intended checkpoint behavior was deliberately dropped. The rebuild additionally fixes queued-write starvation after successful or failed SQL, and a five-second busy-truncate wait plus incorrect admission after a concurrent WAL reset.

The original had 53 expanded SQLite cases; the replacement has 58, using shared fixtures and 849 added test lines versus 2,074 originally. All 82 focused SQLite/terminal cases pass, as do focused lint, formatting and shared typecheck. Three full Opus/Sol review rounds are complete; both latest reviews found no blockers. The original author is credited in both replacement bodies and the top commit history.

Closing this in favor of the linked stack. The latest truncate fix is pushed; hosted CI is rerunning and the changed checkpoint defaults still require human approval. Nothing has been merged. Linux and isolated-server proof, operational limits, and unverified platforms are recorded in the replacement bodies.