docs(multi-bot): A2A worker URL base convention + transition trigger naming

docs/multi-bot-integration.md

@@ -66,3 +66,31 @@ Bridge response is strict webhook-compatible JSON:
 Then register that bridge endpoint in NullBoiler with protocol `webhook`.
 
 Native pull-mode with `NullTickets` is documented in `docs/nulltickets-nullboiler-nullclaw.md`.
+
+## A2A worker conventions
+
+When a workflow uses `execution: "dispatch"` with `dispatch.protocol = "a2a"`:
+
+- **Worker URL is the base URL.** The dispatcher appends `/a2a` to the configured
+  worker URL itself. Configure `http://host:3000`, not `http://host:3000/a2a` —
+  the latter produces `POST /a2a/a2a` and fails with `HTTP 404`.
+- The dispatcher sends A2A v0.3.0 JSON-RPC (`message/send`, `kind` discriminators,
+  `messageId`), requires the worker to accept it at `POST {base}/a2a`, and parses
+  the reply from `result.parts[0].text` (falling back to the legacy
+  `result.artifacts[0].parts[0].text`). Only the first part is read — multi-part
+  replies are not combined.
+
+## Workflow transition conventions
+
+`on_success.transition_to` is passed to the pipeline FSM as the **trigger**
+name. Define the pipeline transition's `trigger` to match the value used in the
+workflow (naming the trigger after its target state, e.g. `trigger: "done"` for
+`to: "done"`, is the simplest convention). A trigger name that does not exist on
+the task's current stage is rejected by the tracker and the task re-enters its
+retry cycle.
+
+`on_failure.transition_to` follows the same naming convention, but is currently
+an **existing implementation gap**: it is parsed and never consumed. After retry
+handling, `Tracker.driveFailed` calls `failRun` directly, so no failure
+transition fires (#52, closed without merge). Treat failure transitions as the
+intended contract, not current behavior.