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).

docs/journals/INDEX.md

@@ -25,3 +25,4 @@
 - 2026-05-12 — iter cma.2: harness binary + 4 tasks + reference solutions + 4 integration tests (six modules, real-pipeline preflight via verify_references, 13/13 tests green; pipeline.rs renames program file to module-name for ail check) → 2026-05-12-iter-cma.2.md
 - 2026-05-12 — iter cma.3: live Qwen3-Coder-Next run + DESIGN.md §Decision-6 empirical addendum + roadmap close (AILX 2/4 green vs JSON 1/4; ~98k vs ~207k tokens; single-subject scope explicit, multi-subject expansion queued as P3) → 2026-05-12-iter-cma.3.md
 - 2026-05-12 — audit-cma: milestone close (Cross-model authoring-form test) — architect drift fixed in 2 record-keeping items (INDEX backfill for brainstorm Step 7.5, README test-count correction); bench all-green (5 unexplained improvements on latency.explicit_at_rc not coupled to milestone, baseline left pristine) → 2026-05-12-audit-cma.md
+- 2026-05-12 — iter ms.1: pipeline anyhow-chain preservation — `{e}` → `{e:#}` at `pipeline.rs:118` restores `serde_json` parse-error leaf in JSON-cohort feedback; pinning unit test added (14/14 green) → 2026-05-12-iter-ms.1.md