Detect open PR conflicts after reconcile and auto-rebase safe task branches

Problem

Extend task-manager reconcile so it discovers open PR-backed tasks even when root frontmatter is stale, probes mergeability after cleanup/startup checks, auto-rebases clean stale-branch conflicts onto main when safe, and escalates true semantic conflicts that need manual resolution.

Context

• Current conflict detection already exists in scripts/task_manager_lib.py:
• refresh_pr_ci_for_tasks() probes GitHub PR state/CI/mergeability
• apply_pr_ci_attention() emits pr_conflict when pr_mergeable == CONFLICTING
• The recent failure on PR #835 showed the actual gap:
• the worktree task file had PR metadata and GitHub reported a conflicted PR
• the root task file still had no pr_number
• heartbeat therefore never probed mergeability for that task at all
• The new auto-reconcile and startup/post-pull reconcile work should reduce stale root metadata, but open PR conflict handling still needs a dedicated pass.
• Relevant files likely include:
• scripts/task-manager-heartbeat
• scripts/task_manager_lib.py
• scripts/task-manager-start
• tests/scripts/test_task_manager_scripts.py
• Constraint: automatic repair must be narrow and safe. It should auto-rebase only when the branch is clean and the conflict is clearly a stale-base problem. True semantic conflicts should become explicit attention/escalation, not silent rewrite attempts.

Possible Solutions

• Option 1: Detect conflicts only and leave rebases fully manual. Low risk, but it preserves operator toil and leaves easy stale-base conflicts sitting around. Rejected.
• Option 2: Recommended Add a post-reconcile PR-conflict pass that:
• discovers open PR-backed tasks from root metadata, register/worktree state, and dispatch artifacts
• probes mergeability for open PRs after reconcile/startup checks
• attempts an automatic git fetch && git rebase origin/main && push --force-with-lease only when the task branch/worktree is clean and the rebase applies without manual conflict resolution
• emits explicit escalation when rebase fails or the branch has local drift This addresses the common stale-branch case while keeping real conflicts visible.
• Option 3: Attempt full automatic conflict resolution for all task PRs. Too risky for hot task-manager files and active task worksheets; likely to create silent bad merges. Rejected.

Plan

1. Extend task-manager PR discovery so reconcile can locate open PR-backed tasks even when root frontmatter is missing or stale.
2. Add a conflict-check phase after reconcile/startup refresh that probes mergeable/mergeStateStatus for open PRs.
3. Implement a narrow auto-rebase helper for safe cases only: - clean branch/worktree - open PR against main - no uncommitted changes - rebase succeeds without manual conflict resolution
4. Surface results in snapshot/history: - auto-rebased PRs - escalated conflicted PRs - skipped unsafe branches
5. Add focused tests for: - stale root metadata but discoverable PR-backed branch - clean stale-branch auto-rebase - rebase failure escalation - dirty worktree skip
6. Document operator expectations so people know which conflicts will self-heal and which still require manual takeover.

Implementation Progress

• Added PR discovery by branch/worktree state when root frontmatter is stale:
• inspect_dispatch() now carries branch
• TaskInfo now tracks branch_name
• discover_pr_backed_tasks() fills pr_number, pr_url, and pr_state from gh pr list --head <branch>
• Added narrow safe auto-rebase helper:
• auto_rebase_conflicted_pr_tasks() only acts on open conflicted PRs
• requires an existing clean task worktree
• runs git fetch origin main, git rebase origin/main, and git push --force-with-lease
• skips dirty or missing worktrees and records attention instead of guessing
• Added a standalone operator command:
• scripts/task-manager-reconcile-pr-conflicts
• scripts/task-system/reconcile-pr-conflicts
• Added focused tests for:
• stale-root PR discovery from dispatch branch metadata
• clean auto-rebase path
• dirty-worktree skip path
• Trialed the command against task auto-reconcile-merged-prs-and-orphaned-in-progress-tasks-in-task-manager / PR #835:
• PR discovery succeeded
• safe auto-rebase did not run because the task worktree is dirty (ahead 19, behind 13 with tracked deletions)
• this is the intended first-pass safety behavior; the tool currently avoids discarding uncommitted task work

QA Exploration

• [x] QA exploration completed (or N/A for non-UI tasks)
• N/A: backend/orchestration task

Review Feedback

• [ ] Review cleared