fix(missions): #54 — the worker was killing live microVM runs at 180 seconds

My hypothesis in #54 was WRONG, and it was wrong because I built it on a bad
measurement: `grep -c 'microvm phase'` returned 0, so I concluded the completion
log never printed and blamed the 15-minute reaper. The line was there all along, at
14:17:45. The real cause is worse.

`requeue_stale` has NO TIER FILTER. A microvm run's `updated_at` is written once at
insert and never again — it is driven by a `tokio::spawn` that owns it start to
finish, and nothing in `microvm_executor` writes `topology_runs`. So at 180s the
sweeper declared a perfectly healthy run stale and flipped it to `queued`;
`claim_next_queued` (no tier filter either) handed it to the worker; `run_job`
tried to parse the microvm graph placeholder, which `TopologyGraph` cannot
deserialize; and it failed the run with "missing or invalid graph".

Mission 019fd43e: run created 14:11:16, mission failed ~14:14:46. 210 seconds — the
180s window plus a tick. The agent went on working and finished at 14:17:45 with
three modules written, by which time the phase was already dead and the VM was
orphaned. A firecracker process was still alive 1h37m later.

THE UNCOMFORTABLE PART: every microVM mission that appeared to work this session
did so only by finishing inside three minutes. The 90-second ones dodged this. The
harness scenario dodges it. Nothing about that was visible.

`WORKER_DRIVEN_TIERS` (team, company, org, swarm, compare) is now the allowlist for
all three sweep paths — claim, requeue, reap. An allowlist rather than a denylist so
the next self-driven tier is safe by default instead of exposed until someone
remembers the file. `tier='session'` had exactly the same exposure and is covered
too. A unit test asserts microvm and session are NOT in it, next to the code that
inserts them.

Two more fixes from the same wreckage:

  - `destroy` reported `killed: pgid.is_some()` — true whenever there was a pgid to
    signal, whether or not anything died. It now sends the signal, polls /proc for
    the group leader, retries, and reports what it OBSERVED; `signalled` keeps the
    old meaning so "nothing to kill" is distinguishable from "it would not die".
  - the run-status update is now guarded with `AND status <> 'cancelled'`. An
    operator cancelling is a decision; this task reporting an outcome minutes later
    is an observation, and it must not overwrite one with the other.

And the root cause of the collect timeout itself: `mission_fs::pack_dir` shipped
`target/` in both directions. `mission_delivery` has excluded build output from the
DIFF since day one; the TRANSPORT never knew. The host checkout was 9.4 MB of which
8.9 MB was `target/`, tarred and base64'd over vsock each way. `EXCLUDED_PATHS` is
now one list shared by both layers, matched on directory name at any depth so a
workspace's per-crate `target/` dirs are all covered.

483 tests pass, clippy clean.

crates/cm-db/src/repo/topology_runs.rs

@@ -203,32 +203,67 @@ pub async fn check_ephemeral_teardown(
     }))
 }
 
+/// Tiers the topology worker drives, and therefore the only ones it may claim,
+/// requeue or reap.
+///
+/// **A load-bearing allowlist, not tidiness.** Both sweepers were written when
+/// every `running` row was a `cm_orchestrator` job that checkpointed after each
+/// step. `tier='microvm'` and `tier='session'` broke that assumption: they are
+/// inserted directly as `running` by `phase_runner`, driven by a `tokio::spawn`
+/// that owns them start to finish, and they never write `updated_at` or
+/// `checkpoint` while in flight.
+///
+/// Measured cost of the omission: `requeue_stale` flipped an in-flight microVM run
+/// to `queued` at 180s, `claim_next_queued` handed it to the worker, and the worker
+/// failed it with "missing or invalid graph" — a microvm run's graph is a
+/// placeholder `TopologyGraph` cannot parse. Mission 019fd43e died at 210 seconds
+/// with its agent still working and its VM orphaned. Every microVM mission that
+/// appeared to work did so only by finishing inside three minutes.
+///
+/// An allowlist rather than a denylist on purpose: the next self-driven tier is
+/// then safe by default, instead of exposed until someone remembers this file.
+pub const WORKER_DRIVEN_TIERS: &[&str] = &["team", "company", "org", "swarm", "compare"];
+
+/// The allowlist as owned strings, for binding as `text[]`.
+fn worker_driven() -> Vec<String> {
+    WORKER_DRIVEN_TIERS.iter().map(|s| (*s).to_string()).collect()
+}
+
 /// Atomically claim the oldest queued job, flipping it to `running`. Uses
 /// `FOR UPDATE SKIP LOCKED` so multiple workers never claim the same job.
 /// Returns `None` when the queue is empty.
 pub async fn claim_next_queued(pool: &PgPool) -> Result<Option<ClaimedTopologyRun>, DbError> {
-    let row = sqlx::query!(
+    use sqlx::Row as _;
+    // A runtime query rather than `query!` so the tier allowlist can be bound
+    // without regenerating the offline metadata on a machine with no database.
+    let row = sqlx::query(
         "UPDATE topology_runs
          SET status = 'running', started_at = COALESCE(started_at, now()), updated_at = now()
          WHERE id = (
              SELECT id FROM topology_runs
              WHERE status = 'queued'
+               -- Defence in depth. Even if a self-driven row somehow reaches
+               -- `queued`, the worker must not adopt a job it cannot execute:
+               -- doing so is what turned a live microVM run into a
+               -- missing-or-invalid-graph failure.
+               AND tier = ANY($1)
              ORDER BY created_at
              FOR UPDATE SKIP LOCKED
              LIMIT 1
          )
          RETURNING id, workspace_id, task, graph, checkpoint, last_event_id, tier",
     )
+    .bind(worker_driven())
     .fetch_optional(pool)
     .await?;
     Ok(row.map(|r| ClaimedTopologyRun {
-        id: r.id,
-        workspace_id: r.workspace_id,
-        task: r.task,
-        graph: r.graph,
-        checkpoint: r.checkpoint,
-        last_event_id: r.last_event_id,
-        tier: r.tier,
+        id: r.get("id"),
+        workspace_id: r.get("workspace_id"),
+        task: r.get("task"),
+        graph: r.get("graph"),
+        checkpoint: r.get("checkpoint"),
+        last_event_id: r.get("last_event_id"),
+        tier: r.get("tier"),
     }))
 }
 
@@ -325,12 +360,19 @@ pub async fn current_status(pool: &PgPool, id: Uuid) -> Result<Option<String>, D
 /// touch within `older_than_secs`). The next claim resumes them from checkpoint.
 /// Returns how many were requeued.
 pub async fn requeue_stale(pool: &PgPool, older_than_secs: f64) -> Result<u64, DbError> {
-    let result = sqlx::query!(
+    let result = sqlx::query(
         "UPDATE topology_runs
          SET status = 'queued', updated_at = now()
-         WHERE status = 'running' AND updated_at < now() - make_interval(secs => $1)",
-        older_than_secs,
+         WHERE status = 'running'
+           AND updated_at < now() - make_interval(secs => $1)
+           -- Only jobs the WORKER drives. A self-driven run (microvm, session) is
+           -- owned by its own task for its whole life and never touches
+           -- `updated_at`, so without this every one of them looked stale after
+           -- three minutes and was requeued out from under a live VM.
+           AND tier = ANY($2)",
     )
+    .bind(older_than_secs)
+    .bind(worker_driven())
     .execute(pool)
     .await?;
     Ok(result.rows_affected())