audit: webhook-event/cache-write-through symmetry for issues.* and pull_request.*

[chrisleekr]

Surfaced during the review of #129. After fixing the issue_comment.edited/.deleted subscription gap, two adjacent surfaces still rely on lazy backfill rather than webhook write-through:

1. src/app.ts:104 subscribes only issues.labeled / issues.unlabeled. No issues.edited or issues.deleted subscription. The issue body is cached in target_cache via upsertTarget, but upsertTarget is currently only called from backfillFromGitHub (src/db/queries/conversation-store.ts:257). A user editing the issue title or body in flight is not reflected in target_cache until a cold-miss backfill happens.
2. src/app.ts:108 subscribes only pull_request_review.submitted. No write-through for review body edits/deletions.

Both are weaker bugs than #129 because the backfill path will fetch fresh data on first read, so the staleness window is bounded by the chat-thread cache hit pattern. But the same class of "the agent reasons against pre-edit text the user thought they changed" applies.

Scope of follow-up:

• Decide whether target_cache should also be write-through (mirroring comment_cache) or whether the lazy backfill is intentional.
• If write-through is wanted, add issues.edited, issues.deleted subscriptions and a corresponding writer in src/webhook/events/issues.ts.
• Audit pull_request.opened/.edited/.closed subscriptions at src/app.ts:85-93 against target_cache writes for the same gap.

Not in scope for #129; tracking separately to avoid PR bloat.

[chrisleekr]

Starting work on this issue — extending the comment_cache write-through pattern shipped in #131 to target_cache.

Decision: write-through (mirroring comment_cache)

The cache header in src/db/migrations/011_conversation_cache.sql already commits to write-through semantics ("a write-through projection of GitHub state"). The current state is just incomplete: only backfillFromGitHub calls upsertTarget, so the target body stays stale until a cold-miss backfill. Adopting full write-through closes the staleness window and matches the documented intent.

Scope

1. issues.* (src/app.ts + src/webhook/events/issues.ts)

• Subscribe issues.opened, issues.edited, issues.closed, issues.reopened, issues.deleted in addition to the existing labeled/unlabeled.
• Add writeIssueTargetCacheThrough(payload) that runs before the label dispatch gate (mirrors the writeCommentCacheThrough pattern in src/webhook/events/issue-comment.ts:32).
  • opened/edited/closed/reopened: upsertTarget with fresh title/body/state from payload.issue.
  • deleted: hard-DELETE the target_cache row (and cascade-delete dependent comment_cache rows for (owner, repo, target_type='issue', target_number)). target_cache schema has no deleted_at, and a deleted issue is gone from GitHub, so soft-delete adds no value.
• Existing labeled/unlabeled dispatch flow is unchanged.

2. pull_request.* (src/app.ts + src/webhook/events/pull-request.ts)

• Add pull_request.edited, pull_request.reopened, pull_request.converted_to_draft, pull_request.ready_for_review to the existing opened/labeled/synchronize/closed subscription list. These are the actions that mutate fields cached in target_cache (title, body, state, is_draft, base_ref, head_ref).
• Add writePrTargetCacheThrough(payload) that runs before all dispatch logic. Always upserts from payload.pull_request — title/body/state/is_draft/base.ref/head.ref. PR delete is not a real GitHub action (PRs close, not delete), so no hard-delete branch.

3. pull_request_review.* — out of scope, follow-up filed if needed

The issue called out pull_request_review.submitted as a write-through gap. I read the code and there is no review-body cache today: comment_cache.surface only permits 'issue-comment' and 'review-comment', and backfillFromGitHub does not fetch reviews. So there is no destination to write through to. Adding review-body caching is a real follow-up but it requires a schema migration (new surface = 'review' value, or a new column on target_cache/new table) and a backfill change — too big to bundle here without expanding #129's blast radius. I will file a follow-up issue if no existing one covers it.

Files to change

• src/app.ts — expand subscription lists.
• src/webhook/events/issues.ts — add writeIssueTargetCacheThrough and call it on every action before the dispatch gate.
• src/webhook/events/pull-request.ts — add writePrTargetCacheThrough and call it on every action before dispatch gates.
• src/db/queries/conversation-store.ts — add deleteTarget({owner, repo, targetType, targetNumber}) helper that DELETEs the target row plus its comment_cache rows.
• test/webhook/events/issues-cache.test.ts (new) — behaviour + subscription invariant tests, mirroring test/webhook/events/issue-comment-cache.test.ts.
• test/webhook/events/pull-request-cache.test.ts (new) — same shape for the PR side.

Ordering invariant

For both writers: cache write must complete (or fail loudly into the .catch) before any dispatch gate / early-return / authorize check that could skip later code. Same source-level invariant test #131 added for issue_comment.

Branch: fix/issue-130. Ship via /pr-auto-github.