feat(TASK-016): engine + test fixes from the Phase-1 re-review

- warn-per-retry test via shared test-only WarnCollector (src/testing.rs)
- extraction-placement test: extraction failures are never retried
- is_transient_error: typed reqwest/Elapsed pre-check + anchored 429 matchers
- outcome_from docstring corrected; validator warning for
  fallback+output_schema without state_updates (llm + agent)
- validator error for max_attempts == 0 (llm + agent); runtime backstop kept
- nits: generalized branch-escape error text, Continue payload comment,
  BFS test assignments assert, node_id threaded into AgentNodeExecutor warns
- bundled-graph warning baseline records 3 true-positive step-runner nodes
  (orient, edge_case_sweep, write_handoff) pending state_updates there

src/graph/executor.rs

@@ -575,7 +575,8 @@ pub(super) async fn step(
     match &node.node_type {
         NodeType::Agent(agent_node) => {
             let outcome =
-                AgentNodeExecutor::execute(agent_node, state, ctx, !step_ctx.branch_mode).await?;
+                AgentNodeExecutor::execute(current, agent_node, state, ctx, !step_ctx.branch_mode)
+                    .await?;
             let targets = match outcome {
                 AgentExecutionOutcome::Continue(_) => {
                     static_next_targets(node, current, "agent", step_ctx.branch_mode)?