In default mode, after the memory-updater processes files and SubagentStop
clears dirty-files, a git commit via Bash would re-trigger PostToolUse,
extract committed files via git diff-tree, and re-add them to dirty-files.
This caused the Stop hook to fire again for already-processed files.
Add early-return guard so default mode skips git commit processing (files
are already tracked via Edit/Write hooks). Also fix existing test to run
commit context enrichment in gitmode where it belongs.
408d4019b3