diff --git a/.github/workflows/publish-runtime.yml b/.github/workflows/publish-runtime.yml
index 6a65bd10..e1fd659d 100644
--- a/.github/workflows/publish-runtime.yml
+++ b/.github/workflows/publish-runtime.yml
@@ -168,6 +168,50 @@ jobs:
           assert callable(get_adapter), 'adapters.get_adapter must be callable'
           assert hasattr(BaseAdapter, 'name'), 'BaseAdapter interface broken'
           assert hasattr(AdapterConfig, '__init__'), 'AdapterConfig dataclass missing'
+
+          # Call-shape smoke for AgentCard. Pure imports don't catch
+          # field-shape regressions in upstream SDKs that only surface
+          # at construction time. Two bugs of this exact class shipped
+          # since the a2a-sdk 1.0 migration:
+          #   - state_transition_history=True (fixed in #2179)
+          #   - supported_protocols=[...] (the protobuf field is
+          #     supported_interfaces — caused every workspace boot
+          #     to crash with `ValueError: Protocol message AgentCard
+          #     has no "supported_protocols" field`; fixed alongside
+          #     this smoke)
+          #
+          # This block instantiates the EXACT classes main.py uses,
+          # with the EXACT keyword arguments. If a future a2a-sdk
+          # upgrade renames any of supported_interfaces / streaming /
+          # push_notifications / etc., the publish fails here instead
+          # of breaking every workspace startup. main.py and this
+          # smoke MUST stay in lockstep — adding a kwarg to one
+          # without mirroring it here is the regression vector.
+          from a2a.types import AgentCard, AgentCapabilities, AgentSkill, AgentInterface
+          AgentCard(
+              name='smoke-agent',
+              description='publish-runtime smoke test',
+              version='0.0.0-smoke',
+              supported_interfaces=[
+                  AgentInterface(protocol_binding='https://a2a.g/v1', url='http://localhost:8080'),
+              ],
+              capabilities=AgentCapabilities(
+                  streaming=True,
+                  push_notifications=False,
+              ),
+              skills=[
+                  AgentSkill(
+                      id='smoke-skill',
+                      name='Smoke',
+                      description='no-op',
+                      tags=['smoke'],
+                      examples=['noop'],
+                  ),
+              ],
+              default_input_modes=['text/plain', 'application/json'],
+              default_output_modes=['text/plain', 'application/json'],
+          )
+          print('✓ AgentCard call-shape smoke passed')
           print('✓ smoke import passed')
           "
 
diff --git a/workspace/main.py b/workspace/main.py
index 16b57d7d..f861a411 100644
--- a/workspace/main.py
+++ b/workspace/main.py
@@ -175,14 +175,24 @@ async def main():  # pragma: no cover
     machine_ip = os.environ.get("HOSTNAME", get_machine_ip())
     workspace_url = f"http://{machine_ip}:{port}"
 
-    # v1: AgentCard.url removed; put url+protocol in supported_protocols instead.
+    # v1: AgentCard.url removed; put url+protocol in supported_interfaces instead.
     # v1: AgentCapabilities.inputModes/outputModes removed; move to AgentCard.default_*.
     # v1: pushNotifications → push_notifications (Pydantic field name)
+    #
+    # AgentCard's protocol message uses `supported_interfaces` (plural,
+    # interfaces — see a2a-sdk types/a2a_pb2.pyi:189). The 0.3.x→1.0
+    # migration in #1974 originally used `supported_protocols`, which
+    # the protobuf doesn't expose at all — every workspace boot since
+    # then crashed with `ValueError: Protocol message AgentCard has no
+    # "supported_protocols" field`. The crash didn't surface in the
+    # publish-runtime smoke because the smoke only IMPORTS
+    # molecule_runtime.main, never CALLS the AgentCard constructor.
+    # Don't rename back.
     agent_card = AgentCard(
         name=config.name,
         description=config.description or config.name,
         version=config.version,
-        supported_protocols=[
+        supported_interfaces=[
             AgentInterface(protocol_binding="https://a2a.g/v1", url=workspace_url)
         ],
         capabilities=AgentCapabilities(