capture-file: preserve artifact integrity

[shunichironomura]

Warning

This content was written by an AI agent and must be verified by a human developer. After human verification, this alert may be removed.

Summary

• Preserve each captured file's project-relative path under its hook artifact directory so same-basename files cannot overwrite each other.
• Plan and validate all destinations before mutation, and refuse to overwrite existing artifacts.
• Hash the completed archived bytes; implement move as copy, optional hash, then source removal so open writers cannot mutate the archived inode.
• Add regression coverage for path collisions, existing destinations, archived hashes, and independent moved artifacts.
• Update the capture-file documentation and output examples.

Closes #1081.

Validation:

• just lint
• just test

AI assistance

• AI used: yes — an AI coding agent investigated the issue, implemented the changes, added tests, and drafted this description.
• Human review of AI-assisted code: pending

Breaking changes

• No breaking changes
• Breaking changes; the breaking change label is applied

---

This is part 4 of 4 in a stack made with GitButler:

•  4  capture-file: preserve artifact integrity #1147 👈
•  3  capture-file: constrain globs to the project root #1146
•  2  Add project-root-aware path type #1098
•  1  Fail closed on hook failures #1097

[codecov-commenter]

Codecov Report

❌ Patch coverage is 70.64220% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.51%. Comparing base (1d0437b) to head (be37254).

Files with missing lines	Patch %	Lines
crates/capsula-capture-file/src/lib.rs	70.64%	32 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                          @@
##           capture-file-project-containment    #1147      +/-   ##
====================================================================
+ Coverage                             55.33%   55.51%   +0.17%     
====================================================================
  Files                                    42       42              
  Lines                                  4384     4469      +85     
====================================================================
+ Hits                                   2426     2481      +55     
- Misses                                 1958     1988      +30     

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