test(gq): add the GQ logic test harness, corpus, and fix-regression gate

[azimafroozeh]

What & why

Implements RFC 0045 (GQ logic tests, #584): a query-level regression becomes one small text file instead of a Rust test, and issue-closing PRs are held to carrying one.

• crates/omnigraph/tests/gq_logic_tests.rs walks tests/gq_logic_tests/*.gqt: one self-contained case per file (issue anchor and red_on: provenance, then schema, seed, and query / mutate / restart steps with per-step params and expect).
• Each case runs on the real engine: fresh store, init, load, index builds only when the case needs them, steps in order under a pinned traversal mode.
• Expect modes: unordered (multiset), ordered, error: <substring>, affected: nodes=<N> edges=<M>; number normalization never routes integers through f64.
• The parser is fail-closed: every malformed input is a refusal, and every refusal has a self-test.
• OMNIGRAPH_GQ_BLESS=1 rewrites a failing case's expect rows in place; OMNIGRAPH_GQ_LOGIC_TESTS=<substring> filters cases by file name.
• First corpus, five cases: the two performance: bm25/rrf ranked read + a join materializes the joined column corpus-wide → Arrow 2 GB offset overflow at ~700k+ rows #563 regressions, an ordering-refusal pin, a foreach + mutation + restart round-trip, and a typed mutation error.
• Two new required PR checks in gq-logic-tests.yml: GQ Logic Tests runs the target pre-merge (the workspace job keeps covering it post-merge), and Fix Regression Gate (scripts/check-fix-regression.py) holds every issue the body closes by keyword to a matching issue_N test or .gqt case in the diff, waivable per PR with the no-repro label.
• AGENTS.md gains the contract sentences: logic tests are the default query-behavior medium, every issue fix lands a regression at the cheapest tier that catches it, and #[ignore] messages open with their species.

The nightly heavy-repro job stays deferred until its first tests/repro_issue_*.rs member lands (the job fails on an empty glob by design).

Backing issue / RFC

• Implements RFC 0045, docs/rfcs/0045-gq-logic-tests.md (docs(rfc): add RFC 0043, GQ logic tests #584). docs(rfc): add RFC 0043, GQ logic tests #584 merges first; its implementation: flip rides that branch.

Checklist

• Change is focused (one test target, its corpus, its two CI checks, the AGENTS.md contract, dev-doc edits; no src/ changes)
• Tests added/updated for behavior changes (84 harness tests: 5 corpus cases plus one self-test per refusal; the gate script carries a self-test the CI job runs first)
• Public docs updated if user-facing surface changed (dev-facing only: testing.md, ci.md, branch-protection.md, AGENTS.md)
• Reviewed against docs/dev/invariants.md (test-and-CI diff; no invariant or deny-list item touched)

Local verification

• cargo test -p omnigraph-engine --test gq_logic_tests — 84/84
• cargo clippy -p omnigraph-engine --all-targets -- -D warnings -W clippy::dbg_macro, cargo fmt --all — clean
• scripts/check-fix-regression.py --self-test — ok; plus three scenario runs against this branch's own diff: closing performance: bm25/rrf ranked read + a join materializes the joined column corpus-wide → Arrow 2 GB offset overflow at ~700k+ rows #563 passes (the corpus matches), closing an issue with no test exits 1, the no-repro label waives
• scripts/check-docs.py, scripts/check-agents-md.sh, scripts/check-workflow-action-pins.py — all OK
• cargo test --workspace — not run locally (no src/ changes); CI covers it

Notes for reviewers

• The only engine seam used is the test-only with_traversal_mode pin.
• Two maintainer actions after merge: create the no-repro label, then run scripts/apply-branch-protection.sh (running it earlier leaves open PRs pending on contexts they cannot receive; both new checks already report on this PR).
• The gate reads GitHub's keyword forms fixes #N, fixes: #N, and fixes:#N (leading zeros normalized); URL, cross-repo, GH-N, and no-space fixes#N closings pass unexamined and stay review's job.
• The edited/labeled/unlabeled PR types re-run the gate when a body edit or the label changes its answer; the test job re-runs on them too (accepted cost).
• The PR cache restores but never saves (save-if: push), so per-PR caches cannot evict main's.
• Stricter than the RFC on small points (traversal pin forces index builds, 10000-iteration loop cap, exact-spelling numeric tokens, CRLF and foreign corpus files refused); each flagged on docs(rfc): add RFC 0043, GQ logic tests #584.

Greptile Summary

The PR adds a GQ logic-test harness and corpus together with required CI and branch-protection checks. It also introduces a fix-regression gate, but the gate’s attempted executable-shape validation still accepts ordinary Rust functions.

• Adds the .gqt parser, runner, expectations, filtering, blessing, and initial regression corpus.
• Adds pre-merge GQ testing and issue-fix regression enforcement.
• Documents the new testing tiers and branch-protection requirements.

Confidence Score: 4/5

The PR is not yet safe to merge because the required fix-regression check can pass when an issue-closing change adds no executable regression test.

The gate accepts any suitably named function definition in Rust source files, including ordinary production or helper functions, while the pre-merge workflow only executes the GQ corpus and therefore does not close that enforcement gap.

Files Needing Attention: scripts/check-fix-regression.py

Important Files Changed

Filename	Overview
scripts/check-fix-regression.py	Adds the issue-fix regression gate, but Rust matches remain naming checks that can accept non-test functions.
crates/omnigraph/tests/gq_logic_tests.rs	Adds the parser and execution harness for query-level logic-test cases.
.github/workflows/gq-logic-tests.yml	Adds required pre-merge logic-test and regression-gate jobs.
AGENTS.md	Defines the repository contract for selecting and naming regression-test tiers.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  PR[Pull request] --> Body[Parse closing keywords]
  Body --> Gate[Fix Regression Gate]
  Gate --> Corpus[Match added .gqt case]
  Gate --> Rust[Match added Rust function name]
  Corpus --> Pass[Required check passes]
  Rust --> Pass
  Corpus --> GQ[Run GQ logic corpus]

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[aaltshuler]

Technical review with five inline findings. The focused harness passes 93/93 tests, including all six corpus cases. The canonical workspace suite remains unverified on this SHA because the PR job was skipped and the PR notes that it was not run locally.