feat: neutral GitHub change signals from the #23 audit

[diegomarino]

Implements the shortlist from the #23 signal audit (see the audit matrix posted there), plus three classifier-only classes the audit's candidate list did not contemplate. Refs #23.

New delta classes (all additive, schemaVersion stays 1)

Requiring new compared fingerprint fields (base, PR labels, assignees, reviewRequests):

• review-requests-changed (pr) — the core agent-feedback signal; sorted logins, teams as org/slug, added/removed detail. No profile payloads: names only, consumers follow up via gh.
• assignees-changed (pr, issue) — sorted logins, added/removed detail.
• base-changed (pr) — PR retargeted; prior CI/mergeability context refers to the old base.
• relabeled now fires for PRs too (the PR fetch now collects labels; previously issue-only).

Classifier-only (existing fingerprint fields, zero fetch cost, id-neutral):

• became-conflicting (pr) — inverse of became-mergeable; UNKNOWN mid-recompute still doesn't count.
• converted-to-draft (pr) — inverse of draft-ready.
• comments-removed (pr, issue) — count decreased; previously an opaque updated.

Compatibility

• Upgrade suppression: the mergeStateStatus pairwise rule is generalized to an ADDITIVE_COMPARED_FIELDS list — a snapshot predating a field never fires on its first appearance, and classifiers guard the old side, so a legacy snapshot with a real concurrent change (e.g. a new comment) cannot misfire the new classes. Verified live: a field-stripped snapshot re-run against the real repo produced 0 deltas.
• Delta ids: new compared fields enter to, so each item's id shifts once on its first post-upgrade delta — the documented id policy (ids hash the observed state), not a regression.
• New classes are id-neutral and covered by the existing forward-compat rule.

Verification

• npm run check green: lint, format, 281 tests (19 new: fetch normalization + fail-closed pagination, fingerprint sorting/defaults, one detector case per class, both upgrade cases, detail shapes).
• Live smoke against diegomarino/gh-delta: GraphQL union selection (User/Bot/Mannequin/Team) validates; baseline → idempotent second run (0 deltas) → simulated pre-upgrade snapshot (0 deltas, no burst).

Deliberately not included (per the audit)

Review-comment edit detection (the one true blind spot — cost disproportionate, documented as a limitation), thread-state digest (rare offsetting-churn case), milestone/stateReason/auto-merge/Projects v2 (consumer follow-up from existing deltas).

Release notes for 0.5.0 (consumer-facing)

• relabeled now also fires for PRs (was documented as issue-only). Route on delta.entity, never on the class alone. The contract row carries a "was issue-only before 0.5.0" note.
• Delta ids shift once per item on its first post-upgrade delta (new compared fingerprint fields enter to). Monitors on different gh-delta versions emit different ids for the same observation — upgrade co-posting monitors together to keep cross-monitor dedupe intact. Documented in the contract's id section.

Audit follow-ups folded in (change-audit 2026-08-05)

• 518331f — Codex P2 / audit X6: updated details apply the same additive-field suppression as the detector; no phantom null -> current rows on upgrade ticks (now also covers mergeStateStatus).
• 0fc4c0c — X1: RUNBOOK + watch-loop prompt now list all classes (incl. baseline-state) with corrected relabeled wording; X2/X3 notes in contract.md; X4: GHES schema-age platform note; X7: became-* best-effort caveat; corrected the stale "branch deletion produces no delta" note (deletion bumps updatedAt → opaque updated, verified live).
• f5bb320 — README JSON sample regenerated from fixtures now showcasing review-requests-changed (review approval satisfying the pending request — the documented co-occurrence with review-changed).

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 8af1b840fa

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".