feat(daemon): D10 carriers + E16 ops RPCs + stress test + virtual fab

Completes the daemon's GEM300 surface and adds two new test tiers.

D10 — E87 carriers: CarrierStore gains the HandlerSlot observer pattern
(add_id/slot_map/access_handler). The daemon's id-observer forwards host
S3F17 decisions onto the Subscribe stream as CarrierAction (PROCEED on a
Confirmed transition, CANCEL on CancelCarrier); ReportCarrier drives the
flow tool-side: WAITING creates the carrier + records the slot map,
IN_ACCESS/COMPLETE advance the access FSM (INVALID_OBJECT on unknown,
CANNOT_DO_NOW on an illegal transition).

E16 — operations RPCs: Describe (full name inventory: variables/events/
alarms/commands/constants + device header), FlushSpool (purge or drain),
SendTerminalMessage (S10F1 tool->host, honest CANNOT_DO_NOW when no host
and stream 10 isn't spoolable).

Stream responsiveness: Subscribe/WatchHealth poll at 100ms (was 500ms) so a
cancelled stream frees its sync-server worker thread promptly — this was
found by the new stress test, which hung under Subscribe churn at 500ms.

Tests:
- A randomized concurrent RPC stress case: 4 threads x 250 seeded ops
  (set/get/fire/alarm/control-state/describe + Subscribe churn), asserts no
  failed RPC and a still-responsive engine afterward; prints its seed; a
  strong TSan target.
- A virtual fab (interop/virtual_fab.py + the `fab` compose service /
  tools/spawn_fab.sh): N daemons, each with a secsgem-py host AND a
  secsgem_client tool, driven by seeded random traffic with end-to-end
  invariant checks (set/get round-trips, event->S6F11 and alarm->S5F1
  delivery, command->tool->completion). Verified green at N=3 (~150 ops/eq,
  all commands round-tripped, 0 violations). Wired into run_interop.sh
  (now 13 steps).

Also fixes the CI break from the previous commit: the Python-client lane's
test_values.py step lacked PYTHONPATH=clients/python (now step-level env).

Two bugs found and fixed while building this, both mine from this batch:
1. carrier test hung on a CancelCarrier of a still-NotConfirmed carrier — a
   self-transition the FSM doesn't signal, so the observer never fired and
   the stream Read blocked forever. Fixed to cancel a Confirmed carrier;
   the NotConfirmed edge is documented as a known E87 limitation.
2. the 500ms stream poll above.

Daemon suite 7 cases / 214 assertions; core 475 / 3097; virtual fab green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -73,6 +73,19 @@ services:
       - /app/data
     networks: [secs]
 
+  # A virtual fab: FAB_N secs_gemd equipment in one container (HSMS 5100+i,
+  # gRPC 51000+i). interop/virtual_fab.py attaches a secsgem-py host AND a
+  # secsgem_client tool to every one and drives seeded random traffic.
+  fab:
+    <<: *base
+    depends_on:
+      builder:
+        condition: service_completed_successfully
+    environment:
+      FAB_N: "${FAB_N:-3}"
+    command: ["bash", "tools/spawn_fab.sh"]
+    networks: [secs]
+
   # Python container preloaded with secsgem-py 0.3.0 for cross-validation
   # of our C++ HSMS/SECS-II/GEM implementation against the reference library.
   interop: