fix: branch conflict — check remote refs, not just local

[stackbilt-admin]

Problem

The branch cleanup logic in taskrunner.sh only checks local refs (refs/heads/${branch}) for existing branches before creating a task branch. When a prior task run pushed a branch to remote but the local ref was cleaned up by worktree removal, the stale remote branch goes undetected.

This causes:

1. git push -u origin "$branch" silently fails (remote branch exists with different history)
2. The task is classified as branch_conflict and fails as non-retryable

In AEGIS, this was the #2 failure mode (6 failures in 7 days).

Root Cause

# Line 676 — only checks LOCAL refs
if git -C "$repo_path" rev-parse --verify "refs/heads/${branch}" >/dev/null 2>&1; then

Worktree cleanup removes local branches, but the remote branch persists. Next run skips the entire cleanup block.

Fix Applied in AEGIS Fork

1. Fetch + check both local AND remote refs before branch creation:

git -C "$repo_path" fetch origin --prune --quiet 2>/dev/null || true
local has_local_branch=false has_remote_branch=false
git -C "$repo_path" rev-parse --verify "refs/heads/${branch}" >/dev/null 2>&1 && has_local_branch=true
git -C "$repo_path" show-ref --verify --quiet "refs/remotes/origin/${branch}" 2>/dev/null && has_remote_branch=true

2. Auto-close stale PRs instead of refusing to proceed:

if [[ "$pr_state" == "OPEN" ]]; then
  gh pr close "$branch" --repo "$repo_slug_check" --comment "Superseded by task re-run" 2>/dev/null || true
fi

3. Push with --force-with-lease for clean branch reuse (safe — branch was just created fresh from base):

git push --force-with-lease -u origin "$branch" 2>/dev/null || true

Ref

Applied in Stackbilt-dev/aegis commit d3945d8.

[stackbilt-admin]

Fixed in v1.3.0. Branch cleanup now checks local + remote refs, auto-closes stale PRs, uses --force-with-lease.