security: contain physical miner commands in Stage A

Disable physical control through legacy HTTP/M30 producers, typed admission,
queue dispatch and upgraded Windows executors. Restrict diagnostic transports
to exact read-only operations, with ordinal PowerShell validation before sockets.

Retire unsupported pending/claimed work with atomic, idempotent security audits.
Preserve prior delivery evidence and report unknown outcomes after a prior claim,
including explicitly repaired pending rows. Include containment, cancellation,
concurrency and malformed-payload regressions and the old-Agent cutover runbook.

Validation: independent final application-security revalidation PASS. Two unchanged
baseline source-assertion failures are documented as exceptions. Production release
still requires native Windows validation and verified fencing/stop/drain/upgrade;
server cancellation alone cannot revoke a cached command held by an old Agent.

backend/app/agent_commands/policy.py

@@ -0,0 +1,35 @@
+"""Stage A containment: no current payload authorizes a physical write.
+
+There is deliberately no environment-variable override. Re-enabling physical
+control requires a separately reviewed identity-binding protocol.
+"""
+
+PHYSICAL_CONTROL_DISABLED = "physical_control_disabled_stage_a"
+UNSUPPORTED_COMMAND = "unsupported_command_schema_stage_a"
+READ_ONLY_COMMAND_TYPES = (
+    "poll_known_miners_now",
+    "discover_new_miners",
+    "enrich_match_discovery",
+)
+
+
+def rejection_reason(command_type: str) -> str | None:
+    if command_type == "miner_control":
+        return PHYSICAL_CONTROL_DISABLED
+    if command_type not in READ_ONLY_COMMAND_TYPES:
+        return UNSUPPORTED_COMMAND
+    return None
+
+
+def rejection_execution_outcome(row: dict) -> str:
+    """A current pending state alone says nothing about earlier delivery.
+
+    The repository supplies an explicit pre-transition evidence check while
+    holding the queue row lock. Missing/ambiguous checks and result submissions
+    are unknown. This describes queue delivery, never proof of physical outcome.
+    """
+    if (row.get("previous_status") == "pending"
+            and row.get("no_delivery_evidence") is True
+            and row.get("delivery_reported", False) is False):
+        return "not_dispatched"
+    return "unknown"