feat(scanner): Skip testdata directories by default

[JordanCoin]

Adds testdata to the hardcoded ignore list, alongside vendor and node_modules. Relates to #172.

Why

Fixture repositories under testdata are not the project's source. They are checked-in inputs for tests: scanning them counts fixture files as project files, and a fixture written in a language the file-level edge model does not cover drags the project's reported coverage down with it.

Go's own toolchain takes the same position — go build and the go tool ignore testdata entirely, and have since the beginning — so this matches a convention Go users already have. It is the justification for the default; the coverage effect is the consequence.

An earlier draft of this PR showed a coverage partial → complete before/after. That measurement came from a Swift fixture added by #174, which is not merged, so it does not reproduce on main — it has been removed rather than left as an unverifiable claim.

What actually changes on this repo

main's tracked tree contains exactly one testdata directory: watch/testdata/, seven shell scripts (run_test.sh, test_mcp.sh, and five under output/). Measured with binaries built from origin/main and from this branch, both scanning a clean export of origin/main:

main branch:  Files: 283   structure output contains  watch/testdata/  (7 files, 17.4KB, all .sh)
this branch:  Files: 276   no testdata node in the tree

So the visible effect today is modest and mostly forward-looking: seven shell fixtures leave the file count, and the bare watch/testdata/ directory node leaves the tree. The value is in what it prevents as fixture directories accumulate — this repo's own milestone work adds them steadily.

Can it be turned off? No — and that is worth being explicit about

IgnoredDirs is a hardcoded map in scanner/walker.go, checked on the fast path before gitignore and before any project config. Only and Exclude in .codemap/config.json are additive filters — they narrow what a scan returns, they cannot widen it — so there is no config key, flag, or gitignore negation that puts testdata back into a scan.

The one escape hatch is scanning the fixture directly as the root, and this PR now guarantees that: IgnoredDirs is no longer applied to the walk root, so codemap testdata/, or codemap . from inside vendor/, scans the directory the user actually named. Before that fix the walker matched the root's own base name and returned Files: 0 — no error, no message, just an empty result. ReadExternalDeps gets the same exemption so a manifest sitting at that root is still read.

Anyone who deliberately keeps project source under a directory named testdata will see those files disappear from counts and from the tree, with no way to opt back in short of renaming the directory or scanning it directly. Flagging it plainly: it is a default-behaviour change with no override.

Tests

• TestScanSkipsTestdataDirectories — skipped at top level and nested (internal/testdata/nested/).
• TestTestdataFixtureScansWhenItIsTheRoot — a fixture passed as the scan root still scans, which is how the fixture tests in scanner call BuildFileGraph.
• TestIgnoredDirNameScansWhenItIsTheRoot — a root literally named testdata, vendor, or node_modules scans its files. Fails on the pre-fix walker with returned [], want [app.go] for all three.
• TestIgnoredDirRootStillSkipsNestedIgnoredDirs — the root exemption covers the root only; a nested testdata under a testdata root is still skipped.

Also on this branch

Two fixes ported from open PRs so this branch's CI can go green without waiting on them; both no-op once main carries them.

• Cargo metadata timeout (scanner/rustcargo.go), from @reneleonhardt's perf: Bound repository analysis hot paths #171: buildRustWorkspaceIndex shadowed its caller's ctx with the cargo-metadata deadline, so an expired deadline failed the whole graph build instead of falling back to the manually derived Rust workspace.
• Watch readiness (main.go), the window fix(watch): Treat an unparseable readiness file as not-ready-yet #177 fixes: waitWatchReadiness gave up on the first unparseable read of a readiness file still being written, surfacing as reading daemon readiness: unexpected end of JSON input.

Release note

testdata directories are now skipped by default, matching Go's own toolchain convention and joining vendor and node_modules. Fixture files no longer count as project files or affect a project's reported coverage. Passing such a directory as the scan root still scans it — and now does so for every name on the ignore list, where previously it returned no files.

Verification

go vet ./... clean, gofmt clean, go test ./... fully green on this branch.

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[JordanCoin]

The review findings on this PR's description are correct and both errors are mine. Not pushing while the branch is being patched — recording the acknowledgement.

The before/after in my description cannot be reproduced on main. I wrote:

before:  codemap --deps .  ->  coverage: partial, source: symbol-imports/swift
after:   codemap --deps .  ->  coverage: complete

That partial depends on #174, which is unmerged — it's #174's Swift fixture and #174's symbol-level coverage rule that produce it. Anyone checking against main would find the premise absent. The effect this PR actually has on main today is on the file inventory: testdata paths in the tree drop from 11 to 1. I built that framing while working with #174's changes in my tree and never re-derived it from a clean main, which is precisely the trap of describing behaviour from a working copy rather than from the base.

My "scan a fixture directly by passing it as the root" claim was under-tested. I verified testdata/probe as root, where the root's basename is probe — so IgnoredDirs never sees it. I did not try testdata/ itself as root, where the basename is the ignored name and the scan silently returns zero files. testdata is a plausible working directory in a way vendor isn't, so the pre-existing behaviour matters more here. Making the walker not apply IgnoredDirs to the root directory itself is the right fix, and it should carry a test — my TestTestdataFixtureScansWhenItIsTheRoot passes without covering the case that actually breaks.

The underlying change stands: fixture repositories aren't project source, and Go's toolchain ignores the directory for the same reason. It's the description and the test's coverage that were wrong, not the exclusion.

I'll re-verify the restated body and the root-directory fix against a clean main build once the branch is free, rather than reading the diff and assuming.

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