`_prune_stale_worktrees` runs synchronously before the banner on every
`hermes -w` launch and shells out to git several times per candidate
worktree. On a repo with dozens of accumulated worktrees this dominated
startup: measured 18.5s of a 20.6s cold start, 11.6s on warm repeats.
The `git cherry` patch-equivalence probe was the single largest cost
(9.4s of 11.5s across 24 trees). It is also pure waste on repeat runs: a
tree preserved because it holds unpushed work is re-diff-hashed on every
launch, forever, always reaching the same verdict. On this repo 19 of 24
aged trees were unreapable, so ~11s per launch bought zero reaps.
Two changes, both verdict-preserving:
- Split the loop into a stat-only age filter, a parallel read-only
classification phase (thread pool, bounded to min(8, cpu_count)), and
a serial mutation phase. Only reads are concurrent; unlock/remove/
branch -D stay ordered, so log output and removal order are unchanged.
A pool failure falls back to serial rather than blocking startup.
- Memoize `git cherry` verdicts to
$HERMES_HOME/cache/worktree_merge_verdicts.json, keyed on the exact
`(base_sha, head_sha, max_ahead)` range the verdict was computed from.
Because that key is the complete input to the git call, a cache hit is
identical to recomputation by construction: if either ref moves, the
key changes and real git runs again. Bounded to 1000 entries, written
atomically, and a corrupt/hand-edited cache degrades to recomputation.
Measured on a 44-worktree repo (24 aged candidates):
_prune_stale_worktrees before 11.5s after 2.05s cold / 0.42s warm
hermes -w to banner before 13.9s after 1.79s
Work-preservation is unchanged: all 44 worktrees survived, and every
dirty/unpushed/live-locked guard still fires. Verified the 24 real-tree
verdicts are byte-identical across serial, cold-cache, and warm-cache
runs.
Tests: 75/75 in tests/cli/test_worktree.py (67 existing + 8 new). The
new cache tests were sabotage-verified — swapping the exact-sha key for a
naive path-only key makes two of them fail by deleting a worktree that
had gained unmerged work, which is the data-loss case the key prevents.
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