Preserve inner error codes through the skills lock-state wrap

[samuv]

Summary

• Follow-up to the Record project-scope skill installs in the lock file #5894 panel review (deferred minor, promised in the review reply; tracked under Track: Skills lock file + Sigstore signing (RFC THV-0080) #5899). installAndRegister wrapped every recordLockState failure as HTTP 500 — but dependency materialization runs inside recordLockState, so a dependency's specific failure (502 from a git resolve, 404 from a registry miss) was masked to 500 at the API boundary, and classifySyncFailure reported unknown instead of the typed reason (registry-unreachable/digest-missing) that CI automation keys on.
• The wrap now attaches 500 only when the inner chain carries no httperr code. Code-less failures — e.g. an actual lock file write error — keep defaulting to 500, and the errLockWrite sentinel classification is unchanged.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Test plan

• New unit test: an install whose declared dependency fails to resolve surfaces the resolver's 502 through Install (was 500 before the fix)
• Extended existing test: a pure lock-write failure still surfaces as 500
• task test and task lint-fix pass locally

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.89%. Comparing base (e047b0d) to head (aa6dda6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5966      +/-   ##
==========================================
+ Coverage   71.85%   71.89%   +0.03%     
==========================================
  Files         714      715       +1     
  Lines       73415    73502      +87     
==========================================
+ Hits        52755    52846      +91     
+ Misses      16879    16872       -7     
- Partials     3781     3784       +3     

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