feat(diagnostics): add fail-closed editor decorations

[seonghobae]

Scope

Stacked implementation lane for Task 3 of PR #248's writing-diagnostics plan. This Draft targets feat/writing-diagnostics-projection; the current projection/contract/design heads are explicit dependencies.

Current stack authority

• current parent: feat/writing-diagnostics-projection@5e49f37278bbdfb2b074fcdb809f72400d96a926;
• current exact head: 93230d80895735f4f0b02a600296c19a2c3be56a;
• inherited architecture: ADR 0028 host-owned revision-bound diagnostics + ADR 0029 strict invalidation / semantic-neutral accessibility;
• live protected release source remains main@e8109ec2a17de8bd6594487aa12c8c8a93cb2c03 under release: reconcile Office and npm versions before next stable registry publication #118.

The previous body still named predecessor parent/head identities and historical main@a430b1c… as current; those claims are superseded.

Product boundary and TDD lineage

This lane renders only already-validated structural ranges. Decorations contain static Inkspan classes, visual priority, and an opaque diagnostic identifier; they do not carry source text, title, explanation, replacement, category text, model output, executable markup, or semantic ARIA authority.

Earlier RED→GREEN evidence established the decoration/invalidation contract, hostile metadata containment, and the semantic-neutral accessibility correction. The forged ariaInvalid: 'spelling' regression failed before production repair; the production field/type/normalization/DOM attribute were then removed and the hostile fixture was retained as an out-of-contract runtime attack case.

The plugin:

• installs diagnostics by monotonic generation;
• bounds decoration count and identifier size;
• invalidates the complete generation on every docChanged transaction rather than remapping stale host/model output;
• focuses only an identifier in the exact active generation;
• rejects hostile metadata/array boundaries without leaking private thrown values; and
• performs no model/provider/network/database/host-callback/semantic inference.

Exact-current-head evidence

For unchanged exact head 93230d80895735f4f0b02a600296c19a2c3be56a, focused Writing Diagnostics Decorations TDD run 31966903293 completed successfully after inheriting current ADR 0028/0029 and projection authority.

This focused success does not transfer to descendants and is not a substitute for the final repository-wide exact-head gates. Any later parent/head movement requires fresh evidence.

Integration boundary

This PR remains Draft and stacked. PRs #248, #249, and #254 are dependency roots that must converge first. Temporary branch-specific TDD workflow material must not survive protected integration. Final readiness requires current canonical CI/security/SAST/coverage/package/browser/accessibility/review evidence, zero valid unresolved findings/contradictions, qualifying independent approval under live governance, and release-order authorization after #118.

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 8b389365-9cd3-4fe7-b884-ad3b37ab4f74

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}