The session container rolls the repo back to an old commit

Symptom

HEAD        : d45e9008 (old commit)
origin/main : 7f08c3ba
48 commits behind

Recurred four times in a single thread.

Why it's dangerous

• Work without noticing and you layer old code on top of already-merged fixes (un-fixing them)
• The whole test count is void. Green is green for the old code.
• It's silent. No error.

Detection

• Human eyes: *a recently merged file or symbol is missing.* An import that should be there is gone (measured: import re vanished), the test count dropped sharply, a function you just wrote isn't there. That is an immediate git log --oneline -1.
• Automatic: a SessionStart hook reports HEAD == origin/main as the first line of every session. For environments without hooks, pin it as step 1 of session start in the project guidelines too.

Rules

• Before any work: git fetch origin main → confirm HEAD matches. Mismatch means resync before starting.
• The hook detects and reports only. No auto-reset. It would throw away uncommitted work.
• Report full-test results only when run after resync, with HEAD pinned.

Caught in the act

The hook caught the fourth occurrence. Uncommitted files were evacuated to the scratchpad, the repo resynced, the files restored. Not adding auto-reset was the right call.

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