fix(P29): SSM fail-loud without CMK + Terraform-rendered invoke policy (P1-3, P1-6)

---ci---
project: acdl
phase: 29
milestone: v1.8
status: execute
---/ci---

P1-3: SSM publisher now raises RuntimeError when ACDL_KMS_KEY_ID is
unset. ACDL_ALLOW_DEFAULT_KMS=1 escape hatch for local testing.
P1-6: consumer_invoke_policy.json now uses ${account_id} and ${region}
placeholders. Terraform renders them via data.aws_caller_identity +
data.aws_region + replace() at apply time. No more hardcoded 000000000000.

Tests: +7 (285 -> 292). All pass.

core/output_publisher.py

@@ -52,7 +52,23 @@ def _ssm_client():
 
 
 def _kms_key_id():
-    return os.environ.get(KMS_KEY_ID_ENV, "alias/aws/ssm")
+    """Return the KMS key ID for SSM SecureString encryption.
+
+    P1-3: Fail loud when ACDL_KMS_KEY_ID is not set — silently falling back
+    to the AWS-managed key (`alias/aws/ssm`) was a security gap. The platform
+    CMK must be explicitly configured. Set ACDL_ALLOW_DEFAULT_KMS=1 to use
+    the AWS-managed key as an escape hatch for local testing.
+    """
+    key_id = os.environ.get(KMS_KEY_ID_ENV)
+    if key_id:
+        return key_id
+    if os.environ.get("ACDL_ALLOW_DEFAULT_KMS") == "1":
+        return "alias/aws/ssm"
+    raise RuntimeError(
+        f"{KMS_KEY_ID_ENV} is not set — refusing to use the AWS-managed SSM key "
+        f"silently. Set {KMS_KEY_ID_ENV} to your platform CMK ARN, or set "
+        f"ACDL_ALLOW_DEFAULT_KMS=1 to use alias/aws/ssm (escape hatch for local testing)."
+    )
 
 
 def publish_to_ssm(outputs, environment, contract_id):