fix(stack): keep squash --message temp file alive across rebase conflicts

[jd]

stack_squash with -m writes the new commit message to a temp file
and inserts an exec git commit --amend -F <tmpfile> line in the
rebase todo. The previous code wrapped the rebase in try/finally so
the temp file was unlinked even when the rebase failed mid-way (e.g.
conflicts on a fixup line that runs before the exec). After the user
resolved conflicts and ran git rebase --continue, git would replay
the exec line and fail because the message file no longer existed.

Drop the finally; only unlink on the success path. If the rebase
raises SystemExit, the file persists so --continue can still execute
the amend. The temp file lives in /tmp and gets cleaned by the OS.

Same pattern (and same fix) as stack_reword — flagged by Copilot on

#1384 review.

[mergify]

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[Copilot]

Pull request overview

Adjusts stack_squash -m/--message to avoid deleting the temporary commit-message file when an interactive rebase stops mid-way (e.g., due to conflicts), so git rebase --continue can still replay the inserted exec git commit --amend -F <tmpfile> line successfully.

Changes:

• Removes the try/finally cleanup around the temp message file in stack_squash.
• Unlinks the temp message file only after a successful run_action_rebase completion.
• Adds inline rationale explaining why the file must persist across conflict-driven rebase interruptions.

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[jd]

Revision history

#	Type	Changes	Reason	Date
1	initial	a87e24c		2026-05-08 13:16 UTC
2	content	a87e24c → ab5c073 (raw)	address copilot review: reword the /tmp comment to system temp directory; add test that monkeypatches run_action_rebase to raise SystemExit and asserts the message file persists for git rebase --cont…	2026-05-08 13:16 UTC

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-05-11 08:34 UTC · Rule: default
• ✅ Checks passed · on draft merge queue: embarking main (25c2d4f) and #1386 together #1400
• ✅ Merged — 2026-05-11 08:49 UTC · at ab5c073f5042b0eb460dd1d395becdcf00f53da8 · squash

This pull request spent 14 minutes 45 seconds in the queue, including 14 minutes 23 seconds running CI.

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