Add workflow to prime chanmon_consistency fuzz corpus

[joostjager]

Add a manual workflow for priming the persistent chanmon_consistency_target honggfuzz corpus with known interesting inputs.

The goal is to preserve failing or challenging fuzz strings discovered during larger offline runs and feed them back into regular CI, so current and future code keeps being exercised against those cases instead of letting the inputs get lost. The workflow restores the latest rolling main corpus, decodes comma-separated hex seeds from the dispatch input into the chanmon consistency corpus, and saves a fresh main-prefix cache entry for subsequent fuzz runs to restore.

The normal fuzz job still owns execution and minimization. Once the primed cache is picked up by a main fuzz run, honggfuzz minimization removes duplicate or non-contributing inputs, so only seeds that add useful coverage remain in the rolling corpus.

Tested on my fork.

[ldk-reviews-bot]

👋 Thanks for assigning @TheBlueMatt as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[ldk-claude-review-bot]

I've thoroughly reviewed the entire diff, cross-referencing with the existing fuzz infrastructure in build.yml and my prior review notes. Let me verify there are no issues I may have missed.

Key areas checked:

• Shell injection: ${{ inputs.seeds_hex }} is routed through env: (line 30), not interpolated in run:. Safe.
• Hex validation: ^([[:xdigit:]]{2})+$ (line 51) correctly enforces even-length, non-empty hex.
• Newline handling: Line 44 normalizes newlines to commas before read on line 45. Addressed prior review concern.
• Cache key interaction: fuzz-corpus-refs/heads/main-prime-${{ github.run_id }} (line 70) is correctly discoverable by the main fuzz job's restore-keys: fuzz-corpus-refs/heads/main- prefix (build.yml:258). The prime workflow first restores the latest corpus, layers seeds on top, and saves — so the primed cache is a superset of the latest main corpus.
• Permissions: Minimal (actions: write, contents: read) with refs/heads/main guard.
• No checkout needed: Only manipulates the cached workspace directory; no repo files required.
• Empty field handling: [ -n "$SEED_HEX" ] || continue (line 50) correctly skips empty fields from consecutive commas/newlines.
• File uniqueness: primed-$GITHUB_RUN_ID-NNNN naming ensures no collisions across runs.

No issues found.

The prior review's inline comment about newline handling is correctly addressed in the current code (line 44). No new bugs, security vulnerabilities, or logic errors identified.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.17%. Comparing base (42e198c) to head (0c23530).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4578      +/-   ##
==========================================
+ Coverage   87.15%   87.17%   +0.02%     
==========================================
  Files         161      161              
  Lines      109251   109251              
  Branches   109251   109251              
==========================================
+ Hits        95215    95243      +28     
+ Misses      11560    11534      -26     
+ Partials     2476     2474       -2     

Flag	Coverage Δ
fuzzing-fake-hashes	31.15% <ø> (+<0.01%)	⬆️
fuzzing-real-hashes	22.93% <ø> (+0.01%)	⬆️
tests	86.24% <ø> (+0.02%)	⬆️

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