Git hooks are slow when .git/entire-sessions fills up

[toothbrush]

What happened?

Sometimes, i end up with lots of files in .git/entire-sessions. These all get parsed when entire hooks git ... commands are invoked. Especially when they're big (multiple megabytes per file isn't unusual for files created before #426 landed) this takes a noticeable amount of time, making Git commands feel unnecessarily sluggish.

Steps to reproduce

$ ls -lah .git/entire-sessions/
total 13M
drwxr-x---  8 paul staff  256 Feb 20 13:16 .
drwxr-xr-x 18 paul staff  576 Feb 20 13:16 ..
-rw-------  1 paul staff 4.3M Feb 20 13:16 2d744384-23a3-4c1f-ae50-6cd8efa9e5c1.json
-rw-------  1 paul staff 4.3M Feb 20 13:16 af9d1e22-c3b0-4225-adc5-0f3bc7355b4d.json
-rw-------  1 paul staff 4.4M Feb 20 13:16 bfa5e680-ceae-4d1a-94f1-f6df47893f0f.json
etc......

$ time entire hooks git commit-msg 1
entire hooks git commit-msg 1  0.48s user 0.05s system 104% cpu 0.512 total

Half a second invocation time for a Git hook that runs frequently is unacceptable.

Entire CLI version

a9a5211

OS and architecture

Darwin 25.3.0 arm64 Darwin

Agent

Claude Code

Strategy

manual-commit (default)