fix(cache): replay missing_dependency tracking in cached_node_modules warm path

[stormslowly]

Why

PR #224 added early-return cache-hit guards to four CachedPath hot accessors. The package_json warm path correctly replays ctx.add_file_dependency / ctx.add_missing_dependency on cache hits, but cached_node_modules was missed.

On the cold path, cached_node_modules → module_directory → is_dir calls ctx.add_missing_dependency(node_modules_path) when the directory doesn't exist. The early-return skipped this, so webpack/rspack file watchers wouldn't receive the signal to rebuild when a node_modules directory was later created.

What

• In the None branch of the warm-cache early-return, call ctx.add_missing_dependency(self.path.join("node_modules")) — mirroring what package_json already does.
• Add a regression test that resolves the same specifier twice (cold then warm) and asserts missing_dependencies is identical on both calls, with a spot-check against the two absent node_modules paths that enhanced-resolve explicitly tracks.

Follow-up

A related cold-path divergence from enhanced-resolve was uncovered while validating this fix: is_dir does not record a missing-dep when the path exists as a non-directory (e.g., a regular file named node_modules). The warm path here happens to handle that case correctly because the OnceLock<Option<CachedPath>> folds "absent" and "non-dir" into the same None. Tracking the cold-path fix separately in #239.

[Copilot]

Pull request overview

This PR fixes ResolveContext::missing_dependencies tracking on warm-cache hits for cached_node_modules, ensuring watcher-integrations (webpack/rspack) still receive “missing node_modules directory” signals after the resolver cache is populated.

Changes:

• Replay ctx.add_missing_dependency(.../node_modules) on cached_node_modules cache hits when the cached result is None.
• Add a regression test asserting cold vs warm resolves produce identical missing_dependencies, including absent traversed node_modules directories.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/cache.rs	Replays missing-dependency tracking on cached_node_modules warm-cache hits.
src/tests/dependencies.rs	Adds a regression test comparing cold vs warm missing_dependencies for absent node_modules dirs.

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[codspeed-hq]

Merging this PR will not alter performance

✅ 12 untouched benchmarks

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_{Comparing fix/cached-node-modules-missing-dependency (9cf97ca) with main (c7167a1)}

[stormslowly]

@codspeedbot explain why this is faster

[codspeed-hq]

@codspeedbot explain why this is faster

Based on my thorough flamegraph analysis, here's the explanation for the user. Since this is a comment response (no code changes needed), I'll provide the answer directly:

Analysis Summary

After analyzing the CodSpeed flamegraphs for both the HEAD and BASE runs, comparing call trees, instruction counts, and the PR's code diff, here's what's happening:

The 4.13% improvement is not directly caused by this PR's correctness fix. It's primarily attributable to PR #237 (skip Box::pin on realpath cache hit) which was merged into main and then flowed into this branch via the merge commit.

Evidence from the flamegraphs

Metric	Before merge with main	After merge with main (HEAD)
Benchmark total	58.1 ms	56.9 ms
realpath::{{closure}} self time	1.4 ms (2.33%)	311 µs (0.55%)
_strip_prefix path operations	2.1 ms (3.64%)	Not present on hot path
metadata calls	15	10

PR #237 restructured the realpath code path so that cache hits return immediately without constructing a Box::pin future or running path normalization (_strip_prefix, Components::next). This eliminated ~3.3 ms of overhead in the realpath sub-tree on the multi-threaded benchmark.

When comparing the two runs on this PR branch (before and after the merge with main), CodSpeed marks all 12 benchmarks as unchanged — confirming the improvement comes from the merge, not from this PR's add_missing_dependency fix.

What this PR actually does

This PR's change — calling ctx.add_missing_dependency(self.path.join("node_modules")) on the cached_node_modules warm path — is a correctness fix with negligible performance impact. It adds a single path join + set insertion to ensure webpack/rspack watchers correctly track absent node_modules directories across cached resolutions. The CodSpeed baseline (59.3 ms) still reflected pre-#237 performance from the recent main branch history, which is why the comparison showed an improvement.

Summary

• Warming up the performance wizard...
• Analyzing performance improvement — Flamegraph analysis complete — preparing explanation
• Handling comment — Comment handling finished successfully