Integrity: preserve exact file bytes in TreeDX unified changesets

[adrianwebb]

Objective

Fix exact-byte source custody discovered during live SDK #293 proposal publication. The proposal source digest in its authoring receipt differs from TreeDX afterSha256 for the same committed file. Investigate unified-diff newline handling; never relabel unequal content as verified.

Acceptance

• Real Git patch round trips preserve exact bytes for create, update, delete, empty files, final-newline changes and trailing blank lines.
• Exact TreeDX read-back matches source digest and changeset afterSha256.
• Repair the live SDK proposal by a normal new authored version; preserve history.
• Automated regressions, Actions and batched RC delivery with API Governance: provision validated proposal-type contracts through library workspaces #336.

Evidence

Live proposal48d5429f-4882-4e89-824e-1866e70e7adb version2, commitc0422b9c1e88d4e15904a0930ce925137b16761b: source receipt da1a29f6b8be4463525c0ea192c1d4c60c6ae55851d150ae56b23f79c5af8f92 vs changeset after d6e3050c2465aca7620e96d384f806dfc8b19dc97958a84723e2faffb16d095f. Do not accept work/review custody before this passes.

Rollback

Retain both authored revisions and audit. Revert code only if needed. No direct protected-ref writes, destructive cleanup or credential changes.