fix(web): prevent writes from incomplete file previews

[saphid]

What Changed

Rendered Markdown task toggles are read-only when the file read is truncated, failed, pending or otherwise unavailable. A toggle rechecks the settled full read and the displayed snapshot before changing a marker. Queued source-editor and task-toggle saves recheck that full-read authority after a pending read settles and before disposal flushes.

Why

A truncated preview could otherwise replace the complete file with its displayed prefix. Cached or optimistic content must not hide a refreshed truncated read or authorize a write after the raw read fails. Valid edits to a complete writable file retain the existing save path.

This does not introduce server-side compare-and-swap, solve every stale complete-read draft, or guarantee BOM/invalid-UTF8 byte preservation. Web and Electron share the affected panel. Native Markdown previews remain read-only. The separate proposal #12666 is not included in this implementation.

Verification

Integrated upstream main at 35be904. All 54 focused tests across six files passed, covering large-file truncation, raw-read failure/pending states, stale marker offsets, query refresh and queued-save/unmount behavior. Web typecheck, scoped lint, formatting and contribution whitespace checks passed.

Direct T3 independent review by Codex / GPT-6.1 Sol, high reasoning requested, completed with no actionable findings across the entire seven-file contribution. The reviewer independently reran all 54 tests and web typecheck and exercised real Effect query-wait/unmount behavior for complete, truncated and failed reads.

UI Changes

Current integrated before/after images and interaction video remain missing, including pending/failed refresh during an edit, closing with a queued save, rendered/source switching and remote file saves. This PR is not yet proven merge-ready.

Historical September 20 captures show the earlier large-file case only: a 1,099,741-byte fixture was reported to shrink to 1,048,576 bytes after a task toggle on base; the earlier candidate disabled the toggle. These captures predate the current integration and save-coordinator repairs and are not current proof:

Before:
After:

Checklist

• I explained what changed and why
• I included current before/after screenshots for all changed UI
• I included a video for interaction changes

Implementation, integration and focused checks: GPT-6 Astra in Codex/T3 Code. Independent source review and checks: GPT-6.1 Sol in Codex/T3 Code.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This production fix changes the preview and save lifecycle by adding read-authority checks and suppressing queued writes after incomplete, failed, or pending reads. Because it gates significant file-write work across existing paths and adds asynchronous coordination, human review is warranted.

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ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

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Run ID: f8407bf4-8ee1-4c10-9d71-f8ff97f80134

📥 Commits

Reviewing files that changed from the base of the PR and between c522e0d and f891e57.

📒 Files selected for processing (6)

• apps/web/src/components/files/FilePreviewPanel.tsx
• apps/web/src/components/files/changeMarkdownTask.test.ts
• apps/web/src/components/files/changeMarkdownTask.ts
• apps/web/src/components/files/projectFilesQueryState.ts
• apps/web/src/components/files/useFileSaveCoordinator.test.tsx
• apps/web/src/components/files/useFileSaveCoordinator.ts

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📝 Walkthrough

Walkthrough

File reads and saves now preserve truncated-read state and check file data before writing. Markdown task updates use a shared helper that validates the current read and displayed snapshot, then passes valid edits to the save coordinator.

Changes

File write authority

Layer / File(s)	Summary
File query authority apps/web/src/components/files/projectFilesQueryState.ts, apps/web/src/components/files/projectFilesQueryState.test.tsx	Query helpers return no data before a successful, completed read. Truncated results take precedence over optimistic file data, with a regression test for that behavior.
Save persistence checks apps/web/src/components/files/useFileSaveCoordinator.ts, apps/web/src/components/files/useFileSaveCoordinator.test.tsx	The save coordinator waits for an outstanding read and rejects missing or truncated data. Tests cover waiting reads, rejected saves, and retry behavior on close.
Markdown task update flow apps/web/src/components/files/changeMarkdownTask.ts, apps/web/src/components/files/FilePreviewPanel.tsx, apps/web/src/components/files/changeMarkdownTask.test.ts	Task edits go through changeMarkdownTask, which checks read authority and snapshot contents before updating query state and calling the save coordinator. Rendered Markdown is read-only for truncated contents, host files, read errors, or pending saves. Tests cover rejected edits and successive edits to the latest draft.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant FilePreviewPanel
  participant changeMarkdownTask
  participant projectFilesQueryState
  participant useFileSaveCoordinator
  FilePreviewPanel->>changeMarkdownTask: Send displayed contents and task marker
  changeMarkdownTask->>projectFilesQueryState: Read current file query data
  projectFilesQueryState-->>changeMarkdownTask: Return complete data or null
  changeMarkdownTask->>useFileSaveCoordinator: Pass updated contents when the snapshot matches
  useFileSaveCoordinator->>projectFilesQueryState: Wait for and check file query data

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Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to f891e

Incomplete or unavailable reads block preview writes, while complete files retain their save path. No actionable issue remains; merge after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to f891e

The change reduces the risk of replacing a complete file with an incomplete preview. A blocked queued edit can remain pending without automatically recovering when the read becomes available again. No broader write access was identified in the inspected paths, but server-side protections were not verified.

Retained concerns

• Low · reliability · observed: The new authority-loss rejection leaves the queued revision unconfirmed and pending, but a later complete read does not itself trigger recovery. A new edit or disposal can retry; if disposal also encounters an incomplete read, the retired session has no subsequent recovery transition. The fail-closed write protection is preserved, but ownership and resolution of the blocked edit remain implicit.

Security review details

Security Blast Radius

• observed — The inspected write paths retain the selected environment, workspace and relative file path when invoking the existing write command. They do not introduce a broader target selector. Effective filesystem permissions and server-side environment isolation were outside the inspected scope.

Security Findings and Attack Paths

• inferred — For the inspected callbacks, an incomplete preview cannot authorize a full-file replacement through the queued-save path: the persistence gate rejects unavailable or truncated reads, including disposal flushes. No newly expanded attack path was established by these changes.

Trust Boundaries and Controls

• observed — The new gate establishes local data-completeness authority, not user or server authorization. Markdown controls are disabled for truncated, host-file, failed and pending states, and the callback independently validates completeness and snapshot identity.
• observed — The complete-read check and write command remain separate operations, without a revision precondition in the inspected request. This pre-existing limitation permits stale complete-read edits or intervening external writes; the PR narrows incomplete-read writes but does not establish compare-and-swap atomicity.

Resilience and Maintainability Implications

• observed — Authority loss fails closed: rejected contents are neither written nor confirmed. The trade-off is that the existing failure branch leaves the revision pending without scheduling another attempt when no newer edit exists, connecting recovery behavior directly to ownership of unsaved state.

Hardening Proposals

• proposed — Define an explicit blocked-unsaved state with a deliberate recovery or discard action. Any recovery should revalidate file identity and the complete snapshot rather than automatically replaying an old draft when a read becomes available.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 9.09% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 7 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing writes from incomplete file previews.
Description check	✅ Passed	The description includes the required What Changed, Why, UI Changes, and Checklist sections. It clearly explains the problem, implementation, scope, verification, and known limitations. Current screen…

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Actionable comments posted: 1

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Inline comments:
In `@apps/web/src/components/files/FilePreviewPanel.tsx`:
- Line 1244: Update the useProjectFileQuery integration and the readOnly
expression near the file preview controls to use the raw query result’s
truncation state in addition to file.data.truncated and isHostFile. Ensure stale
optimistic non-truncated data cannot keep task controls enabled when the
refreshed query result is truncated, while preserving the existing read-only
behavior.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository: pingdotgg/t3code/.coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: e9d8f50b-8c17-4616-aade-b2015dc31904

📥 Commits

Reviewing files that changed from the base of the PR and between b379b5b and 5d4eec5.

📒 Files selected for processing (5)

• apps/web/src/components/files/FilePreviewPanel.tsx
• apps/web/src/components/files/changeMarkdownTask.test.ts
• apps/web/src/components/files/changeMarkdownTask.ts
• apps/web/src/components/files/projectFilesQueryState.ts
• docs/internals/consistency-preview-write-authority.md

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Dismissing prior approval to re-evaluate c522e0d

Dismissing prior approval to re-evaluate f891e57

[juliusmarminge]

Note

This comment is posted by Julius' dot

The supplied clips show the earlier large-file toggle case. The PR explicitly lacks current UI proof for pending or failed refreshes and closing with a queued save. Closing under the verification rule. Add current before/after captures and a short recording of those changed save interactions, then request reconsideration.