Claude Code defaults to rebase+force-push instead of merge when updating branches

Problem

When Claude Code needs to update a branch with changes from the base branch, it defaults to git rebase followed by git push --force-with-lease, even when operating on someone else's PR branch. This is destructive: it rewrites commit history and breaks the other contributor's local checkout.

Expected behavior

• Default to git merge when updating a branch with upstream changes — it's non-destructive and preserves history
• Never force-push to a branch without explicit user approval
• When fixing CI on someone else's PR, just commit the fix and git push — don't rewrite their history at all

What happened

The bot was asked to fix a CI failure (formatting) on another contributor's PR. It:

1. Committed the fix (correct)
2. Rebased the branch onto the base branch (unnecessary, destructive)
3. Force-pushed to the contributor's remote branch (violated its own instructions)

The contributor now cannot git pull normally — they need git reset --hard to recover.

Claude Code's own instructions say

"NEVER run destructive git commands (push --force, reset --hard, ...) unless the user explicitly requests these actions"

Despite this, the bot chose rebase+force-push as its default strategy. This appears to be a trained-in bias toward rebase over merge across LLM coding agents generally.

Suggested fix

• When a branch needs updating with the base branch, always use git merge, not git rebase
• Treat git rebase as a destructive operation requiring explicit user approval, same as push --force
• When working on someone else's branch, minimize history changes — commit the fix and push, nothing more