fuzz: count symlinked fuzz corpus files

[joostjager]

The fuzz CI job links cloned corpus dirs into hfuzz_workspace, but plain find does not descend through those symlinked directories.

Count with find -L so the iteration budget reflects the real corpus size, and fail loudly if a linked corpus resolves to zero files.

[ldk-reviews-bot]

👋 Thanks for assigning @TheBlueMatt as a reviewer!
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.62%. Comparing base (1060865) to head (04808cb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4626      +/-   ##
==========================================
+ Coverage   86.59%   86.62%   +0.02%     
==========================================
  Files         159      159              
  Lines      110420   110420              
  Branches   110420   110420              
==========================================
+ Hits        95619    95647      +28     
+ Misses      12267    12240      -27     
+ Partials     2534     2533       -1     

Flag	Coverage Δ
fuzzing-fake-hashes	6.62% <ø> (+0.05%)	⬆️
fuzzing-real-hashes	23.17% <ø> (+0.01%)	⬆️
tests	86.23% <ø> (-0.01%)	⬇️

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[ldk-claude-review-bot]

I've thoroughly reviewed the PR diff, the existing ci-fuzz.sh script, and the CI workflow in build.yml (which shows how symlinks are created at the input level via ln -sfn). The changes are minimal, focused, and correct:

1. corpus_count() properly uses find -L to follow the symlinks created by CI
2. check_linked_corpus() correctly checks [ -L "$CORPUS_DIR" ] at the input level — which matches where ln -sfn creates the symlink in .github/workflows/build.yml:251-252
3. All three find call sites are updated consistently
4. The check is correctly placed only before fuzzing starts (pre-condition), not after
5. Variables are properly quoted, wc -l always returns a valid integer, and find -L handles symlink cycles gracefully (GNU find emits a warning to stderr, which is already suppressed)

No issues found.

[TheBlueMatt]

thanks

[TheBlueMatt]

Feel like this should warn even if the dir isn't a link, but whatever.

[ldk-reviews-bot]

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