✨ - Browser extension H5 complete review diff and issue collaboration tools #706

Is there an existing issue or feature request for this?

• I have searched the existing issues and feature requests.

What area does this improvement affect?

New Feature

What actions does this improvement affect?

Issue, Pull Request, Commit

Description of the idea or improvement

H5 — Complete review, diff and issue collaboration tools. Part of the complete product from merged PR #699 and milestone GitHub browser extension — complete product. Implementation order does not reduce product scope or the 803-case acceptance floor.

Catalog ownership: REVIEW, ISSUE; 26 required capabilities, 110 distinct mandatory catalog case IDs. Implement every feature record in specs/browser-extension/features/REVIEW.v1.json, specs/browser-extension/features/ISSUE.v1.json.

Implement every REVIEW and ISSUE catalog record, including review/diff navigation, context/readability, conversation helpers, native draft composition and issue workflow aids. Preserve native review threads/editor drafts and GitHub submission ownership; no surprise submit, approval, merge, label mutation or lifecycle authority. Bind review actions to actual repository/object/head and reconcile soft navigation, collapsed/virtualized/outdated nodes and partial results. Show loaded scope and native source links, explicit stale/unsupported/read-only states and actionable retry without duplicate controls.

Normative baseline: specs/github-browser-extension.md, specs/github-browser-extension-functional-catalog.md, specs/github-browser-extension-platforms-and-delivery.md, specs/github-browser-extension-action-integration.md, specs/github-browser-extension-control-center-and-setup.md, and the versioned structured schemas/catalog. Follow specs/README.md and _template.md; update owning SDDs, current catalog evidence, tests and user docs in the implementation PR. Before starting, refine exact current-code acceptance and prerequisite evidence through the Action's pre-branch SDD flow.

Tests and acceptance: Own all family cases with meaningful review/diff/conversation fixtures, draft cancellation, identity/revision changes, permissions, native coexistence and sanitization. Require full keyboard/screen-reader/theme/locale and actual browser matrix for implemented controls; preserve full product human task gates.

All new pure evidence/eligibility/intent/approval policies require 100% branches; other new modules require at least 95% statements/90% branches with changed executable lines covered. Modules at most 220 lines/Svelte components 90 unless reviewed decomposition exception. Add risk-derived cases beyond the baseline where needed; every required behavior maps to executable evidence and docs. Full product acceptance remains all 150 functions/all three desktop targets, not this issue alone.

Current limitations or challenges

PR #699 specifies the product; this milestone's behavior is not implemented merely because the specifications or earlier engineering increments exist. Dependencies: H2 (#703), H3 (#704). Use the roadmap's linked issues to verify those dependencies before starting; do not advertise future features, runtime compatibility or store approval as already verified.

Expected impact

Complete review, diff and issue collaboration tools becomes a complete, tested and documented part of the original premium GitHub productivity application. Users receive observable outcomes, safe defaults and useful failure/recovery paths across Chrome, Firefox and Safari, with explicit source/freshness/permission boundaries where applicable.

Alternatives considered

Reject reduced catalog scope, copied implementation/assets, speculative compatibility claims, placeholder acceptance, duplicate Action authority and weaker existing test gates. Deliver in reviewable increments while retaining the complete accepted product contract.

Version of copilot

Published Action 3.10.5; develop baseline includes merged #699. Extension versions independently; future implementation selects and locks compatible dependencies using primary documentation.

Additional context or comments

Backlog milestone. Do not add in-progress or create a branch until its dependencies are ready and it is deliberately started. The Action owns admission/SDD/remote branch lifecycle. PRs link their issue and include actual test/browser/docs receipts; merge/deploy/store publication is not implied. First active increment: #702.