Three fixes for the reweave merge failure cycle:
1. reweave.py: fetch + reset to origin/main before branch creation,
eliminating the stale-base problem that caused ~75% merge failure rate
2. merge.py: delete remote branch when closing reweave PRs (in reconcile,
merge failure, and conflict retry paths) — prevents discover_external_prs
from rediscovering stale branches and creating new PRs every 18 minutes
3. merge.py: skip cherry-pick retry for reweave branches — reweave modifies
existing files so cherry-pick always fails, go straight to close+delete
Pentagon-Agent: Ship <f3064ef4-c330-4809-ad37-39290b2eaa5b>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>