iter ms.1: pipeline.rs format!("check: {e}") → {e:#} preserves anyhow Caused-by chain in JSON-cohort feedback

Inline pinning test in pipeline.rs constructs the same chain
shape module_name_from_json produces on serde-parse failure
(leaf wrapped with "parsing JSON in <path>" context) and
asserts both layers survive the formatter. RED→GREEN against
the property, not against production line bytes — for a
two-character fix, extracting a helper just for testability
would be over-engineering.

The strip_locations regex collapses \nCaused by: chains; the
{:#} alternate Display joins with ': ' on one line, so the
collapser is a no-op on the fixed output. AILX cohort
unaffected — only the harness-side anyhow path (module
rename pre-check) was dropping cause information.

Harness suite: 14/14 green (was 13/13 + 1 new pin).

bench/orchestrator-stats/2026-05-12-iter-ms.1.json

@@ -0,0 +1,12 @@
+{
+  "iter_id": "ms.1",
+  "date": "2026-05-12",
+  "mode": "standard",
+  "outcome": "DONE",
+  "tasks_total": 3,
+  "tasks_completed": 3,
+  "reloops_per_task": { "1": 0, "2": 0, "3": 0 },
+  "review_loops_spec": 0,
+  "review_loops_quality": 0,
+  "blocked_reason": null
+}