Fix/run hardening prep (#263)

* fix(git): don't delete a branch that still has open dependent PRs

Root cause of the run-zombifying "integration branch gone from origin" wedge.
_delete_remote_branch_best_effort deleted a merged PR's head branch
unconditionally, so:
- merging a cell->root PR deleted the cell branch while a sibling leaf PR was
  still targeting it as base, and
- the CEO's root->master merge deleted the feature/main_pm/{root} integration
  branch.
The dependent PRs lost their base, every later git op against the vanished
branch failed, and the task zombified (a51c3d31 only made the post-merge sync
non-fatal; this removes the cause).

The remote-branch delete chokepoint (the single path all merge/close/cancel
deletions funnel through) now first checks _branch_has_open_dependents: any OPEN
PR targeting the branch as its base marks it an active integration target and
preserves it. Fails safe (any error => keep the branch; cleanup is best-effort,
stranding is not). True leaf branches with no open dependents are still cleaned
up. Adds 6 unit tests for the guard + the probe.

* fix(git): recover a drifted shared clone on resume instead of BRANCH_MISMATCH

A dev/documenter/QA clone is shared across that agent's tasks. On a
respawn/resume it can sit on a sibling task's branch, or a re-provisioned clone
can lack the task branch as a local ref (commits only on origin). The
fresh-claim path git-resets the clone clean, but resume deliberately
short-circuits before it (_dev_reentry), so the agent's next commit hit
_assert_on_task_branch's BRANCH_MISMATCH, failed, and the task wedged in a
blocked respawn loop (the documenter that could never land its doc commit).

_assert_on_task_branch now recovers instead of only rejecting: fetch + checkout
the task branch (recreating a missing local ref from origin via `git branch
<b> origin/<b>`), and raise only when the switch genuinely can't happen
(uncommitted changes block it). Never discards work — checkout, not reset — so
a resumed agent's unpushed commits are preserved. Updates the RAG troubleshooting
+ developer docs to describe the auto-recovery. Adds 5 unit tests.

* fix(runtime): re-adopt running agent containers on restart (no double-spawn)

An orchestrator restart loses the in-memory _instances registry while the agent
containers keep running. The reaper already had a Docker-liveness fallback
(_assignee_container_running), but the spawn gate (_is_agent_active) did not, so
right after a restart it saw a live agent as inactive and could launch a second
container onto work the forgotten-but-running one was already doing.

start() now calls _readopt_running_agents() after _reconcile_orphan_claims_on_startup
and before the dispatcher/reaper loops launch: it probes each known agent slug's
container (AGENT_IMAGES, reusing _inspect_container_state — the same docker
inspect the reaper uses) and registers a minimal AgentInstance(state=ACTIVE) for
any that is running and not already tracked. Inert when nothing runs (cold start
unchanged); best-effort (a probe error leaves that slot for the reaper's own
fallback). This is the gateway-health spec's Task 4 / the orchestrator-state
spec's Phase 3 (_instances reconcile). Adds 4 unit tests.

* fix(git): treat an already-merged PR as idempotent success on merge

A merge PUT against an already-merged PR returns the same 405 as a genuine
"not mergeable" conflict, so _merge_with_retry raised MergeConflictError and the
completion path tried to rebase / close-superseded / escalate a PR that had
already landed (a prior cycle, a sibling, or the CEO merged it) — the
cell_pm_complete block<->unblock respawn loop.

_merge_with_retry now disambiguates before raising: a new _pr_is_merged probe
(GET the PR, check merged==true) returns success on an already-merged PR so
completion proceeds idempotently; a genuinely-unmerged 405 still raises the
conflict. Best-effort probe (False on any error → falls through to the existing
conflict handling). Adds 4 unit tests.

---------

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

docs/rag/roles/developer.md

@@ -69,7 +69,7 @@ There is **no** `roboco_git_commit / _push / _create_pr / _merge_pr / _checkout`
 
 - Branches are auto-created on `i_will_work_on()`.
 - Don't checkout branches by hand — call the verb on the right task.
-- If you see a `BRANCH_MISMATCH` envelope, you're on the wrong task. Use `give_me_work()` again or `unclaim` and re-pick the intended task.
+- A drifted clone (after a respawn/resume) is now auto-recovered onto your task branch before you commit — you normally won't see `BRANCH_MISMATCH` at all. If you still do, uncommitted changes are blocking the switch: `commit(...)` your work (or `i_am_blocked` if the changes aren't yours), then continue.
 
 ## Before Submitting to QA