feat(ha-commit-barrier-rollout): dispatch-gate fact allowlist (task 4.2)

notify/update/setpreason/clrpreason admitted in CTRL_PRIMARY without
write quorum (Req 3.2 / umbrella 2.8 / bug-396): all four terminate in
receipt-style RETAIN fact paths — reviewer-traced no-block proof (no
admitted opcode reaches a barrier/WAIT path; request opcodes stay
rejected). 21/21 group; census 494/494 zero FAIL; RED→GREEN
independently reproduced via stash-rebuild.

src/controller/ha.c

@@ -1561,6 +1561,16 @@ int ha_dispatch_gate(ha_state_t *ha, int opcode)
             /* Read-only queries */
             case OPCode_get:
             case OPCode_probeConfigTag:
+            /* Fact-bearing ops — reports of events that already happened
+             * (worker job transitions/rusage, scheduler pend reasons).
+             * Rejecting them loses the fact forever: the reporter never
+             * retries (bug-396).  Admit so the RETAIN path can append and
+             * hold them until quorum returns (Req 3.2; umbrella 2.8 —
+             * facts are retained, never dropped). */
+            case OPCode_notify:
+            case OPCode_update:
+            case OPCode_setpreason:
+            case OPCode_clrpreason:
                 return 0;
             default:
                 return -XCE_ERR_NOT_READY;