🤖 fix: reduce git lock conflicts in background polling

[ammar-agent]

Problem

Background git polling runs git fetch every 3-60 seconds. Even when there's nothing new to fetch, git fetch acquires maintenance.lock, which can conflict with:

• Manual git commands in terminal
• Agent git operations during streaming

Solution

Check if fetch is needed before acquiring any locks:

1. git ls-remote → get remote SHA (network only, no lock)
2. git cat-file -e → is SHA already local? (no lock)
3. If local → skip fetch (no lock needed)
4. If not local → fetch to get new commits (lock, but only when genuinely needed)

Why this works

# Before: always locks
git fetch  →  maintenance.lock (even if nothing to fetch)

# After: only locks when needed  
ls-remote + cat-file  →  no lock (common case: SHA already local)
git fetch             →  lock (rare: new remote commits)

In practice, IDEs fetch periodically and agent git pull operations keep refs current, so the "already local" path triggers most of the time.

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Generated with mux

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