docs(contract): clarify minimal OCS envelope + reuse _BROKER_READY

Address round-1 review nits:
- document why _ocs_capabilities omits the rest of the OCS envelope (Pact V4
  allows extra provider-side keys; pin only astrolabe's own block)
- use the module-level _BROKER_READY in the broker-source guard instead of
  re-checking the three env vars inline

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

tests/contract/test_astrolabe_capabilities_consumer.py

@@ -36,7 +36,14 @@ pytestmark = pytest.mark.contract
 
 
 def _ocs_capabilities(enabled_doc_types: list[str]) -> dict:
-    """Minimal OCS envelope carrying just astrolabe's semantic_search block."""
+    """Minimal OCS envelope carrying just astrolabe's semantic_search block.
+
+    Intentionally omits the rest of a real OCS response (other apps'
+    capabilities, ``meta.statuscode``/``message``, etc.): Pact V4 allows extra
+    provider-side keys, so pinning only the block this consumer reads keeps the
+    contract focused on what astrolabe owns without coupling to Nextcloud-core
+    envelope fields.
+    """
     return {
         "ocs": {
             "meta": {"status": "ok"},

tests/contract/test_mcp_provider_verification.py

@@ -117,7 +117,7 @@ def test_verify_astrolabe_consumer_pacts() -> None:
     verifier = Verifier(PROVIDER_NAME).add_transport(url=_PROVIDER_URL)
     verifier.state_handler(_dispatch_state, teardown=True)
 
-    if _BROKER_URL and _BROKER_USERNAME and _BROKER_PASSWORD:
+    if _BROKER_READY:
         # selector=True to opt into pending pacts: a new/authenticated contract
         # (e.g. the consent-purge endpoint) reports as *pending* instead of
         # failing this build until provider verification of the authenticated