Task 1's attn_pool gate (commit 7dd953aa) was inside the captured-graph
region, so the host branch's decision was frozen at step-2 capture time.
In Sequential mode this would lock the captured graph to whichever
boundary state happened to hold at step 2, breaking subsequent file-
boundary detection — violating pearl_no_host_branches_in_captured_graph.
Fix: track the boundary state at capture time as a new
`train_graph_boundary_state: Option<bool>` field. On each step_batched,
if the current `last_seen_file_boundary` diverges from the captured
state, drop the cached graph and re-capture on the next step.
- Random mode: gate is unconditionally true; state never diverges;
zero recaptures.
- Sequential mode: ~8 recaptures per epoch (one per file boundary).
Each recapture costs the same as the original step-2 capture (~50ms).
Negligible.
Verified clean cargo check -p ml-alpha --all-targets.
f22f3f9488