fix: prevent git auto-gc from blocking mirror unmount

[adityamaru]

Summary

Fixed a race condition where git's internal auto-gc (triggered by fetch/clone) would spawn a background daemon holding the mirror mount busy during unmount, causing checkout post-step failures. We now suppress auto-gc during fetch/clone operations (gc.auto=0) and run gc explicitly once with proper timeout and error handling.

Root Cause

git fetch and git clone --mirror trigger gc --auto internally. Since gc.autoDetach defaults to true, this forks a background daemon that holds cwd + mmap'd pack files on the mount. Even though our explicit runMirrorGC() uses gc.autoDetach=false, the background daemon from fetch/clone still blocks unmount.

Changes

• Added gc.auto=0 to fetch args to suppress auto-gc during mirror refresh
• Added gc.auto=0 to clone args to suppress auto-gc during initial mirror creation
• Documented the race condition and solution in code comments

Fixes BLA-3202

🤖 Generated with Claude Code

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Note

Low Risk
Small, localized change to git command arguments to prevent background processes; risk is limited to potential differences in GC timing/performance during mirror operations.

Overview
Prevents git mirror cleanup failures by disabling git’s automatic background GC during mirror creation and refresh.

ensureMirror and refreshMirror now pass -c gc.auto=0 to git clone --mirror and git fetch, and add comments explaining that auto-GC can spawn a detached process that keeps pack files/mount busy and blocks unmount; explicit GC remains handled separately.

^{Written by Cursor Bugbot for commit aec22c0. This will update automatically on new commits. Configure here.}

[linear]

BLA-3202 * : add explicit guest+host durability fences (flush) before RBD snapshot; add instrumentation to verify flush propagates and is non-no-op