fix: recognize resolved GitHub review threads in summary

[titouanmathis]

Problem

On GitHub PRs, the review summary keeps re-listing findings in its "Still open from earlier reviews" block even after the human has resolved those threads (observed on studiometa/ui#511, where all 15 bot threads were resolved yet still appeared as open). The reviewer also re-raises already-settled concerns.

Root cause

Both summary paths decide resolution with notes.some((n) => n.resolved === true):

• src/summary-carryover.ts — skips resolved threads when building the carry-over block.
• src/prior-threads.ts — flags a prior thread resolved for the reviewer prompt.

But on GitHub note.resolved was always undefined:

1. normalizeGitHubDiscussions never set it.
2. The data was never fetched — getDiscussions reads the REST endpoints GET /pulls/{n}/comments and GET /issues/{n}/comments, and neither REST endpoint returns thread-resolution state. On GitHub, review-thread resolution lives only in the GraphQL API (pullRequest.reviewThreads.nodes.isResolved).

So every prior thread looked open: resolved findings were carried over indefinitely, and resolved concerns were re-raised. This works on GitLab because its discussions API returns resolved per note inline.

Fix

• Add GitHubClient.listResolvedReviewCommentIds() — paginated GraphQL reviewThreads query returning the database ids of comments in resolved threads. Derives the GraphQL endpoint from the REST base (github.com → /graphql; GHE /api/v3 → /api/graphql) and surfaces GraphQL errors as typed GitHubApiErrors with an actionable hint.
• getDiscussions fetches resolution alongside the two REST calls and passes it to normalizeGitHubDiscussions, which stamps resolved onto each note — mirroring GitLab's per-note field so the shared helpers work unchanged on both platforms.

Tests

• github.test.ts: resolved-id extraction, GHE endpoint, thread pagination, typed error on GraphQL errors.
• platforms/github.test.ts: notes flagged resolved by id; default-unresolved; end-to-end getDiscussions → carry-over exclusion.
• cli.integration.test.ts: in-memory backend now models resolution via GraphQL; new test asserts a resolved prior finding is dropped from the summary (reproduces #511), while the existing unresolved-carry-over test still passes.

npm run check passes (lint, format, typecheck, typecheck:tests, 696 tests, build).

🤖 Generated with Claude Code

[github-actions]

Code Review

Risk: Low — The change appears to address the GitHub resolved-thread carry-over bug without introducing blocking defects, so it is safe to merge.

This MR adds a GitHub GraphQL read path for resolved review-thread state, threads that data through discussion normalization, and reuses the existing shared carry-over / prior-thread helpers via the normalized resolved flag. The test coverage is strong across client, platform, and CLI integration layers, and the implementation matches the stated intent of fixing stale "Still open from earlier reviews" entries for resolved GitHub threads.

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Reviewed by @weareikko/code-review v0.8.2 for commit 02a810c.