feat(file-system): optimistic-concurrency guard on canvas publish by adboio · Pull Request #72365 · PostHog/posthog

adboio · 2026-07-20T16:19:14Z

Problem

posthog desktop canvas publish action (behind the desktop-file-system-canvas-partial-update mcp tool) has no concurrency guard

this is fine right now because every canvas write is a full file replace, but i am changing that (PostHog/code#3594), so version control is more important

Changes

add expected_current_version_idas a concurrency guard on the PATCH; returns 409 on conflict

How did you test this code?

tested e2e manually, paired with PostHog/code#3594

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🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Built with Claude (PostHog Code cloud task) while reworking desktop canvas generation to edit canvases as workspace scratch files (PostHog/code#3594). Skills invoked: /improving-drf-endpoints, /writing-tests. Considered a tool-side check-then-PATCH guard in the agent instead; rejected because only a server-side check inside the row lock is atomic, and this endpoint already owns version composition — one canonical writer beats three divergent ones.

Created with PostHog Code

github-actions · 2026-07-20T16:19:29Z

Hey @adboio! 👋

It looks like your git author email on this PR isn't your @posthog.com address (adambowker98@gmail.com). Since you're on the PostHog team, it's worth pointing your local git author email at your @posthog.com address. Why it matters:

Consistent work identity in git history — internal tooling that attributes commits to team members keys off your @posthog.com address.
Keeps team contributions easy to tell apart from external community ones when scanning history.

You can fix it for this repo with:

git config user.email "you@posthog.com"

Or set it globally with git config --global user.email "you@posthog.com". No need to redo this PR — just a nudge for next time. 🙂

…as action canvas_publish now calls the desktop-fs canvas action, which owns version composition server-side, passing the checkout's version as expected_current_version_id so a stale publish is rejected atomically (409 version_conflict) instead of guarded by a non-atomic tool-side check-then-PATCH. Deletes the tool-side compose logic and the raw meta PATCH; backends predating the guard field ignore it and publish unguarded, so the tool degrades gracefully. Server side: PostHog/posthog#72365. Generated-By: PostHog Code Task-Id: 2b3d176e-3023-41d2-92e8-81eda7c12a8c

The desktop canvas publish action appends a version onto whatever the live head is, so a publisher working from a stale read (a concurrent publish, or a user's undo moving currentVersionId back) silently becomes the new head over newer work. Add an optional expected_current_version_id to the publish payload: when provided and the canvas has moved past it, the publish is rejected with 409 version_conflict (carrying the live version id) inside the existing row lock. Omitting the field keeps the previous unguarded behavior for older callers. Also mirror the client's linear-discard semantics: publishing after an undo now truncates the redo tail past currentVersionId instead of leaving unreachable versions in the history. Generated-By: PostHog Code Task-Id: 2b3d176e-3023-41d2-92e8-81eda7c12a8c

github-actions · 2026-07-20T16:28:03Z

🤖 CI report

✅ Bundle size — no change

Uncompressed size of every built .js bundle, compared against the base branch.

Total: 64.16 MiB · no change

No file changed by more than 1000 B.

_{Posted automatically by build-bundle-size-report · uncompressed bytes from dist-report}

✅ Eager graph — within budget

How much code each root ships on the eager path — downloaded and parsed before the surface is interactive. Measured from the esbuild output chunks (post-tree-shake, static imports only); lazy import() / React.lazy chunks are not counted.

Root	Eager (shipped)	Δ vs base	Budget
entry (logged-out pages, app bootstrap) `src/index.tsx`	1.23 MiB · 22 files	no change	`███░░░░░░░` 28.6% of 4.29 MiB
authenticated shell (every logged-in page) `src/scenes/AuthenticatedShell.tsx`	8.18 MiB · 2,997 files	no change	`█████████░` 88.4% of 9.25 MiB

🟢 node_modules/monaco-editor/ stays out of src/index.tsx
🟢 src/lib/components/ActivityLog/describers stays out of src/index.tsx
🟢 [object Object] stays out of src/index.tsx
🟢 [object Object] stays out of src/index.tsx
🟢 node_modules/monaco-editor/ stays out of src/scenes/AuthenticatedShell.tsx
🟢 src/lib/components/ActivityLog/describers stays out of src/scenes/AuthenticatedShell.tsx
🟢 [object Object] stays out of src/scenes/AuthenticatedShell.tsx
🟢 [object Object] stays out of src/scenes/AuthenticatedShell.tsx

Largest files eagerly shipped from src/index.tsx

Size	File
126.8 KiB	`../node_modules/.pnpm/react-dom@18.3.1_react@18.3.1/node_modules/react-dom/cjs/react-dom.production.min.js`
24.6 KiB	`../node_modules/.pnpm/buffer@6.0.3/node_modules/buffer/index.js`
6.3 KiB	`../node_modules/.pnpm/react@18.3.1/node_modules/react/cjs/react.production.min.js`
4.5 KiB	`../node_modules/.pnpm/@jspm+core@2.1.0/node_modules/@jspm/core/nodelibs/browser/process.js`
3.9 KiB	`../node_modules/.pnpm/scheduler@0.23.2/node_modules/scheduler/cjs/scheduler.production.min.js`
1.4 KiB	`../node_modules/.pnpm/base64-js@1.5.1/node_modules/base64-js/index.js`
1.3 KiB	`src/RootErrorBoundary.tsx`
912 B	`../node_modules/.pnpm/ieee754@1.2.1/node_modules/ieee754/index.js`
789 B	`src/scenes/ChunkLoadErrorBoundary.tsx`
762 B	`src/index.tsx`

Largest files eagerly shipped from src/scenes/AuthenticatedShell.tsx

Size	File
281.3 KiB	`../node_modules/.pnpm/posthog-js@1.404.1/node_modules/posthog-js/dist/rrweb.js`
267.7 KiB	`../node_modules/.pnpm/@posthog+icons@0.38.0_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/@posthog/icons/dist/posthog-icons.es.js`
235.5 KiB	`src/taxonomy/core-filter-definitions-by-group.json`
223.4 KiB	`../node_modules/.pnpm/posthog-js@1.404.1/node_modules/posthog-js/dist/module.js`
164.0 KiB	`src/queries/validators.js`
154.3 KiB	`../node_modules/.pnpm/re2js@0.4.1/node_modules/re2js/build/index.esm.js`
126.8 KiB	`../node_modules/.pnpm/react-dom@18.3.1_react@18.3.1/node_modules/react-dom/cjs/react-dom.production.min.js`
105.9 KiB	`src/lib/api.ts`
93.3 KiB	`../node_modules/.pnpm/prosemirror-view@1.40.1/node_modules/prosemirror-view/dist/index.js`
93.2 KiB	`../packages/quill/packages/quill/dist/index.js`

_{Posted automatically by check-eager-graph · sizes are eager output bytes (shipped, post-tree-shake) from the esbuild metafile · part of #32479}

✅ Dist folder size — 🔺 +3.9 KiB (+0.0%)

Total size of the built frontend/dist folder (all assets), compared against the base branch.

Total: 1344.14 MiB · 🔺 +3.9 KiB (+0.0%)

✅ Playwright — all passed

All tests passed.

View test results →

adboio · 2026-07-20T16:29:28Z

feat(file-system): optimistic-concurrency guard on canvas publish #72365 👈 (View in Graphite)
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posthog · 2026-07-20T17:04:26Z

🦔 ReviewHog reviewed this pull request

Found no issues worth raising, so no review was posted.

github-actions · 2026-07-20T17:36:18Z

🦔 Hogbox preview · ✅ ready

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🧩 Running	this PR's backend and frontend, on the PostHog `:master` base
🔗 Link	stable across rebuilds — a re-push swaps the box underneath, the URL stays
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_{commit 9bec143 · box box-7d0736525e20 · ready in 807s (push → usable) · build log · rebuilds on every push, torn down on close}

greptile-apps · 2026-07-20T17:38:13Z

_{Reviews (1): Last reviewed commit: "chore: update OpenAPI generated types" | Re-trigger Greptile}

stamphog

Additive, backward-compatible API contract change (optional guard field, unguarded behavior preserved when omitted) with parameterized tests covering exactly the failure modes that matter (false-positive guard, fail-open on stale/null base, undo/redo truncation), and it's already been reviewed by Greptile (agent reviewer) plus a 👍 from the security bot with no concerns raised.

👍 on the PR from greptile-apps[bot], hex-security-app[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	109L, 2F substantive, 275L/9F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1d-complex (275L, 9F, cross-cutting, feat)
stamphog 2.0.0b3		`.stamphog/policy.yml` @ `d5d244c` · reviewed head `9bec143`

deployment-status-posthog · 2026-07-20T19:08:07Z

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-07-20 19:08 UTC	Run
prod-us	✅ Deployed	2026-07-20 19:22 UTC	Run
prod-eu	✅ Deployed	2026-07-20 19:26 UTC	Run

…as action canvas_publish now calls the desktop-fs canvas action, which owns version composition server-side, passing the checkout's version as expected_current_version_id so a stale publish is rejected atomically (409 version_conflict) instead of guarded by a non-atomic tool-side check-then-PATCH. Deletes the tool-side compose logic and the raw meta PATCH; backends predating the guard field ignore it and publish unguarded, so the tool degrades gracefully. Server side: PostHog/posthog#72365. Generated-By: PostHog Code Task-Id: 2b3d176e-3023-41d2-92e8-81eda7c12a8c

assign-reviewers-posthog Bot assigned adboio Jul 20, 2026

adboio mentioned this pull request Jul 20, 2026

feat(canvas): edit canvases as scratch files via canvas_checkout / canvas_publish PostHog/code#3594

Draft

2 tasks

chore: update OpenAPI generated types

9bec143

adboio force-pushed the posthog-code/canvas-publish-version-guard branch from a28994d to 9bec143 Compare July 20, 2026 16:29

adboio marked this pull request as ready for review July 20, 2026 17:35

adboio added the stamphog Request AI approval (no full review) label Jul 20, 2026 — with Graphite App

github-actions Bot deployed to preview-pr-72365 July 20, 2026 17:36 View deployment

stamphog Bot approved these changes Jul 20, 2026

View reviewed changes

adboio merged commit f8967ac into master Jul 20, 2026
388 of 429 checks passed

adboio deleted the posthog-code/canvas-publish-version-guard branch July 20, 2026 18:32

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feat(file-system): optimistic-concurrency guard on canvas publish#72365

feat(file-system): optimistic-concurrency guard on canvas publish#72365
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