Trigger Observability In The Action Graph

Harn now projects trigger activity into persisted run observability across both workflow-derived nodes and dispatcher hops. The current surface includes trigger, predicate, dispatch, and a2a_hop nodes, plus the matching trigger_dispatch, predicate_gate, and a2a_dispatch edges.

What lands in this change

• A synthetic trigger node is added when a run carries a trigger_event envelope in run.metadata.
• Workflow condition stages render as predicate nodes in observability.action_graph_nodes.
• Local dispatch attempts render as dispatch nodes.
• Remote A2A dispatch attempts render as a2a_hop nodes labelled with the resolved target_agent.
• Entry edges from the trigger node into the workflow render as trigger_dispatch.
• Trigger or predicate edges into a remote A2A hop render as a2a_dispatch.
• Transitions leaving a predicate on the workflow path render as predicate_gate.
• trace_id propagates from the TriggerEvent onto the synthetic trigger node and every downstream action-graph node derived from that run, including A2A hops.

The runtime also streams the derived graph onto the shared event-log topic observability.action_graph whenever a run record is persisted. This reuses the generalized EventLog infrastructure instead of a parallel observability bus.

Current shape

This scoped change still leaves some portal/runtime work deferred:

• Landed here: trigger, predicate, dispatch, and a2a_hop node kinds.
• Deferred: worker_enqueue specialized nodes and richer DLQ/A2A UI.
• Deferred: portal replay controls and dispatcher-coupled UI work.

Example

When a workflow is started with a trigger_event option, the persisted run record will include observability nodes like:

{
  "kind": "trigger",
  "label": "cron:tick",
  "trace_id": "trace_123"
}

and:

{
  "kind": "predicate",
  "label": "gate",
  "trace_id": "trace_123"
}

with edges such as:

{"kind": "trigger_dispatch", "from_id": "trigger:...", "to_id": "stage:..."}
{"kind": "predicate_gate", "label": "true"}
{"kind": "a2a_dispatch", "from_id": "predicate:...", "to_id": "a2a:..."}

The portal does not yet render specialized UI for these nodes in this PR; it will consume the shared event-log topic in the dispatcher follow-up.