fix(aw-transform): empty regex rules never match

[TimeToBuildBob]

Summary

• An empty regex pattern compiles to a match-all regex in fancy_regex, so RegexRule::new("") silently categorized/tagged every event.
• aw-core's Python aw_transform.classify.Rule deliberately never matches on an empty regex ("would erroneously match everything"). aw-server-rust diverged from that behavior.
• fix(categories): treat blank regex rules as matching nothing everywhere aw-webui#1026 hides this for the web UI by sending blank rules as {type: 'none'}, but other clients (aw-client categorize queries, scripts, the CLI) still see the divergence.
• Adds a never_matches flag on RegexRule, set when the source pattern is empty, checked before any regex evaluation on both the select_keys and shared-values match paths.
• New regression test test_empty_regex_never_matches (fails on master, passes after the fix).

Unrelated CI note

This branch also carries the clippy::block_scrutinee allow from #771/#772 (Rust 1.99+ clippy toolchain drift in the generated aw-query parser, unrelated to this change) so this PR's own CI passes independently of whether #771 has merged yet. Once #771 merges first, that one-line diff here will disappear on rebase.

Test plan

• cargo test -p aw-transform — 79 passed, 0 failed
• Confirmed the new test fails on master without the fix (reverted the one-line guard locally, reproduced the failure, restored it)
• cargo clippy --workspace -- -D warnings clean
• cargo fmt --check clean

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Fixes regex rule matching logic for empty patterns.

The PR appears safe to merge; the previously reported empty-regex conversion path is fixed.

Summary

The PR makes empty regex rules never match, including when constructed through the public Rule::from(Regex) conversion.

• Adds regression coverage for both construction paths.
• Adds a Clippy allowance for the generated query parser.

_{Reviews (2) · Last reviewed commit: "fix(aw-transform): derive never_matches ..."}

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.59%. Comparing base (656f3c9) to head (144d324).
⚠️ Report is 169 commits behind head on master.

Files with missing lines	Patch %	Lines
aw-transform/src/classify.rs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #774       +/-   ##
===========================================
+ Coverage   70.81%   82.59%   +11.77%     
===========================================
  Files          51       81       +30     
  Lines        2916    10428     +7512     
===========================================
+ Hits         2065     8613     +6548     
- Misses        851     1815      +964     

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[TimeToBuildBob]

@greptileai review

[TimeToBuildBob]

CI-green and mergeable (Greptile 5/5) — waiting only on a maintainer click.

This PR is ready to merge, but the bot has pull-only access to this repo and can't self-merge — surfacing it here so it isn't lost. The monitoring loop will stop re-flagging it now that this note is posted.

[TimeToBuildBob]

🤖 AI code review

This PR adds a never_matches flag to RegexRule in aw-transform/src/classify.rs, set when the source regex pattern is empty, and checks it before any regex evaluation in both value_matches and matches. It also adds a regression test test_empty_regex_never_matches and updates the clippy allow list in aw-query/src/lib.rs to include unknown_lints and clippy::block_scrutinee.

Safe to merge — no P0/P1 findings

Confidence 5/5

✅ No thread-worthy findings. Advisory notes follow; they are retained without opening review threads.

1 advisory finding (summary-only, not scored)

These P2 guard, heuristic, trade-off, or documentation claims are retained for judgment without opening review threads.

⚠️ P2 medium — aw-transform/src/classify.rs

This is a fix(...) PR but no test files are included in the diff. Erik's feedback: 'where is the repro & fixes they are supposed to catch' (gptme#3441), 'that measurement should come with a regression test' (gptme#3446). Add a test that would have caught this bug. (Advisory: Erik merged all such PRs but consistently requested tests.)

Add a test file that reproduces the bug before the fix and passes after it.

_{How this was verified: static preflight: fix-commit + touched-files scan (rule 7)}

Files changed (2) — the diff as I read it

• aw-query/src/lib.rs — Adds unknown_lints and clippy::block_scrutinee to the clippy allow list on the parser module.
• aw-transform/src/classify.rs — Adds never_matches flag to RegexRule, sets it from empty pattern in new and From<Regex>, checks it in value_matches and matches, and adds a regression test.

_{Reviewed 144d324cc70e · openrouter/deepseek/deepseek-v4-flash-0731 · llm engine · 72s · about this reviewer}

_{Maintainer commands}

_{@TimeToBuildBob review (own line) — fresh review · @TimeToBuildBob fix — a worker acts on the findings. Once per comment; 👀 = received.}