verify(P18): onboarding-schema-and-lambda-action — 4-layer verify PASS + ship

VERIFY: structural — schema + Lambda action; behavioral — 41 tests + CI PASS; quality — pending CMDB row (D-119, no AWS resources).

---ci---
project: acdl
phase: 18
milestone: v1.16
status: complete
phase_role: execution
requirements:
  covered: [REQ-182]
  partial: []
---/ci---

core/lambda/contract_ingestor.py

@@ -398,6 +398,65 @@ def _validate_change_request(payload):
     }
 
 
+def _onboard_consumer(payload):
+    """P18 (REQ-182): accept a self-service onboarding request.
+
+    Validates the payload against schemas/onboarding.schema.json, then
+    writes a 'pending' row to nova-contracts (D-119). No AWS resources
+    are created by this action (D-113); the cross-account role + ABAC
+    tag grant is offline-proven Terraform (P20/REQ-184).
+    """
+    import jsonschema
+    schema_path = os.path.join(os.path.dirname(os.path.dirname(
+        os.path.dirname(os.path.abspath(__file__)))),
+        "schemas", "onboarding.schema.json")
+    try:
+        with open(schema_path) as f:
+            schema = json.load(f)
+        # Strip the Lambda dispatch envelope (action) before validating
+        # against the onboarding schema (the schema is about the request,
+        # not the Lambda wrapper).
+        onboarding_payload = {k: v for k, v in payload.items() if k != "action"}
+        jsonschema.validate(instance=onboarding_payload, schema=schema)
+    except OSError:
+        raise ValueError("onboarding schema unavailable")
+    except jsonschema.ValidationError as e:
+        raise ValueError(f"onboarding payload invalid: {e.message}")
+
+    consumer_repo = payload["consumerRepo"]
+    requested_env = payload["requestedEnvironment"]
+    owner_id = payload["ownerId"]
+    billing_tag = payload["billingTag"]
+    submitted_at = _iso8601_now()
+
+    # Write a pending CMDB row (PK consumerRepo, SK onboarding#env#timestamp).
+    table = _get_dynamodb().Table(TABLE_NAME)
+    item = {
+        "consumerRepo": consumer_repo,
+        "contractId#submittedAt": f"onboarding#{requested_env}#{submitted_at}",
+        "contractId": f"onboarding-{requested_env}",
+        "environment": requested_env,
+        "status": "pending",
+        "ownerId": owner_id,
+        "billingTag": billing_tag,
+        "notes": payload.get("notes", ""),
+        "submittedAt": submitted_at,
+    }
+    table.put_item(TableName=TABLE_NAME, Item=item)
+    return {
+        "status": "pending",
+        "consumerRepo": consumer_repo,
+        "requestedEnvironment": requested_env,
+        "action": "onboard_consumer",
+        "submittedAt": submitted_at,
+        "message": (
+            "Onboarding request received. The platform team will provision "
+            "the environment binding + cross-account role. Track the status "
+            "via the nova-contracts table (status=pending → granted)."
+        ),
+    }
+
+
 def lambda_handler(event, context):
     """AWS Lambda handler entry point.
 
@@ -426,6 +485,8 @@ def lambda_handler(event, context):
             result = _report_error(payload)
         elif action == "validate_change_request":
             result = _validate_change_request(payload)
+        elif action == "onboard_consumer":
+            result = _onboard_consumer(payload)
         else:
             return {
                 "statusCode": 400,