roles --role dead -T: hand-authored test fixture directories aren't excluded, causing reachability noise

[carlos-alm]

Summary

While validating #2032's transitive-reachability dead-code fix by running codegraph roles --role dead -T on this repo's own src/, I found that the bulk of the newly-flagged-dead nodes (50 of 53 in the final delta) come from directories that are clearly test infrastructure but aren't excluded by -T:

• tests/benchmarks/resolution/fixtures/** — the hand-authored, per-language (34 languages) resolution-precision fixture projects documented in CLAUDE.md's Test Structure section (expected-edges.json manifests).
• tests/benchmarks/resolution/tracer/** — the dynamic call tracers (loader-hook.mjs, python-tracer.py, lua-tracer.lua, r-tracer.R, php-tracer.php, etc.).
• tests/fixtures/sample-project/** — the ES-module sample fixture (math.js/utils.js/index.js).

None of these filenames match TEST_FILE_PATTERNS (%.test.%, %.spec.%, %__test__%, %__tests__%, %.stories.% in src/graph/classifiers/roles.ts / the mirrored Rust TEST_FILE_PATTERNS) — they're plain source files (main.c, service.ml, validators.gleam, reflection.kt, ...) that happen to live under a tests/ directory, which the current filename-suffix-only heuristic doesn't check for.

Why this matters

These fixtures are deliberately tiny, self-contained per-language snippets with no genuine external entry point recognized by codegraph's own root-detection (no CLI/MCP/exported-and-called-cross-file signal) — they exist purely to exercise parser extraction precision/recall. Before #2032, direct fan-in alone kept most of their internal call chains classified non-dead; #2032's stricter reachability check (correctly) now flags almost everything in these disconnected components as dead, since nothing in them is a confirmed-live root by any of codegraph's own criteria.

This isn't a bug in #2032's logic — it's a pre-existing gap in -T's test-file detection becoming more visible now that dead-code classification is stricter. It affects any analysis that relies on -T to scope to "real" application code (roles --role dead -T, triage -T, audit -T, etc.), not just the new reachability pass.

Suggested fix

Extend the test-file exclusion heuristic (TEST_FILE_PATTERNS / testFilterSQL in src/db/index.ts and the mirrored Rust TEST_FILE_PATTERNS/test_file_filter_col in crates/codegraph-core/src/graph/classifiers/roles.rs) to also recognize path-based test/fixture markers, e.g. any path segment matching tests/, fixtures/, __fixtures__/, or similar — needs care to avoid over-broadly excluding legitimately-shipped code that happens to live under a test-utils-style production directory.

Related

• roles --role dead: non-transitive fan-in means a function called only by another dead function is never flagged dead #2032 — the transitive-reachability fix whose self-build validation surfaced this