Workflow parent retry loses a deferred route when the node also writes deltas #7930

Description

A workflow node that sets ctx.route and pending state/artifact deltas without yielding another event loses its route from the final persisted event. The returned Context still holds the route, so the initial execution selects the correct branch. A parent retry reconstructing the nested workflow from events cannot recover the route, and the selected branch silently ends instead of retrying its failed node.

class Router(BaseNode):
  async def _run_impl(self, *, ctx, node_input):
    ctx.output = 'routed'
    ctx.route = 'go_b'
    ctx.state['visited'] = True
    return
    yield  # async generator with deferred context output

The final event has output routed and state delta {'visited': True}, but event.actions.route is None. Artifact-only deltas and combined state/artifact deltas show the same problem. A route without deltas survives.

Root cause

NodeRunner._flush_output_and_deltas constructs Event(route=...), then replaces the entire event.actions object with an EventActions containing only the deltas. The newly assigned actions discard the route. Reusing _flush_deltas, which merges into the existing actions, preserves it.

End-to-end impact

A real Runner executes an outer driver node with a two-attempt retry policy, invoking a nested workflow router -> {'go_b': flaky_b, 'go_c': node_c}. flaky_b fails on its first call and succeeds on its second. On main, the router runs once but flaky_b runs only once: recovery emits a warning that no edge matches route None and returns without the selected result. With the route preserved, the router still runs once, flaky_b runs twice, node_c never runs, and the expected output is produced.

Verification

Reproduced on main 95d8610 with real Runner and InMemorySessionService, no model/cloud service. Three delta combinations fail in a per-node regression (no-delta control passes), and the conditional parent-retry integration regression fails too.

AI assistance: Codex investigated and reproduced the problem.