fix(plane): ax task lifecycle -- resume, stay-up runner, delivery as completion

The first live run on the local ax cluster and ax's source (docs/runner.md,
docs/sandbox.md, internal/controller/reconciler.go, internal/server/server.go)
showed a lifecycle the task-3/4 code did not model:

- `ax apply` creates a Task Suspended (Ready=False, TaskSuspended); it runs only
  after `ax resume task`. The first resume of a new image can fail with
  DeadlineExceeded while Agent Substrate builds the golden snapshot, and ax's
  server then stores phase Failed; a later resume succeeds.
- ax has no Completed phase and never reads a command's exit back.
- The runner is PID 1 and must keep serving after the command exits; stop and
  suspend deliver SIGTERM, to be forwarded to the command's process group.
  Our runner imported the task in-process and exited, which stopped the
  container ("Container guest is stopped") and made every resume time out.
- ax's controller probes /readyz?check=workspace; the query string made our
  handler answer 404.

Runner (Req 4.1-4.4): spec.command runs as a child
`python -m openultrasast.plane.tasks.<name>` in its own process group, cwd the
first workspace, AX_METADATA_URL set; ax's metadata paths are served. After the
child exits the runner reads summary.json (a crash without one becomes failed
with the exit code and stderr tail), delivers the output directory, writes
/workspace/.ousast-state/<task>.done.json and serves until SIGTERM (forwarded
to the group, SIGKILL after OUSAST_TERM_GRACE, exit 0). A boot with the marker
never reruns the command; a failed delivery is retried alone. Workspaces are
prepared on the first boot only. AX_RUNNER_EXIT_AFTER_COMMAND=1 is the
unit-test escape.

Reconciler (Req 2.2, 2.3, 3.1-3.3): `ax resume task` after apply, retrying
DeadlineExceeded/Unavailable with backoff up to OUSAST_RESUME_TIMEOUT (900 s);
completion is the artifact delivery; Failed after a resume went through, a
vanished task, or no delivery within OUSAST_TASK_TIMEOUT (7200 s) fail the
task with ax's condition message; `ax delete task` follows. Ax gains resume()
and phase() returns the condition message. doctor moves to plane/doctor.py
(tasks.md task 0 allows the sibling) to keep reconciler.py under 500 lines.

Tests: the fake ax follows the real lifecycle (Suspended, a failing first
resume that leaves Failed, Running forever, delivery only after a resume went
through), plus Failed-with-message, vanish, resume-timeout and task-timeout
scenarios; runner tests cover the child's cwd/group/metadata URL, stay-up and
SIGTERM in a real subprocess, SIGKILL of a SIGTERM-ignoring group, and the
marker. The opt-in live test now checks resume, Running, suspend and a second
resume instead of a Completed phase. design.md and tasks.md state the
lifecycle; the module audit manifest counts plane.doctor.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

benchmarks/measurements/2026-09-08-module-audit.json

@@ -1,7 +1,7 @@
 {
-  "modules": 128,
+  "modules": 129,
   "counts": {
-    "load_bearing": 119,
+    "load_bearing": 120,
     "standalone_capability": 9
   },
   "orphaned": [],
@@ -673,6 +673,14 @@
         "plane.tasks.verify"
       ]
     },
+    {
+      "module": "plane.doctor",
+      "classification": "load_bearing",
+      "reason": "reachable from gate, map_gate, pair_gate or the CLI",
+      "importers": [
+        "plane.reconciler"
+      ]
+    },
     {
       "module": "plane.manifests",
       "classification": "load_bearing",