feat(verdicts): key each verdict on its own candidate, not the bundle's one IR projection (S3.2)

seed_store_from_bundle keyed EVERY `type: verdict` file on bundle_candidate_features — the single
candidate the bundle's validator-input.json describes. A bundle carrying verdicts about several
candidates collapsed them onto one key, so a verdict about candidate B scored a perfect structural
match against candidate A's query and could be folded into A's hypothesis prompt. The ExpeL
substrate was single-candidate by construction.

A verdict file may now carry its own structural key in frontmatter (affected_codes / measure_type /
claimed_saving_nok); absent, keying falls back to the bundle candidate, so every pre-S3.2 seed keeps
working unchanged. promote_verdict writes the three fields, so a promoted verdict — frequently about
a different candidate than the target bundle's projection — does not impersonate that candidate.

Semantics decided HERE, not pulled: commons' seeding rule (method-spec §3 Steg 1 + bundle example)
has not arrived; we said we would build locally first. D7 mirroring stays open.

- ALL THREE fields or none. A partial declaration raises VerdictFrontmatterError rather than merging
  with the bundle candidate, which would mint a key belonging to NEITHER candidate. Validation,
  never repair (mirrors write_concept_file); the tolerant-skip rule belongs to the RAW inbox layer.
- claimed_saving_nok parses via json.loads — the SAME literal rule the IR projection went through —
  and is written back with str() of the raw value. _mint_id hashes that value, so 30000 and 30000.0
  are different keys; a normalising writer would split one candidate's signal across two ids.
- The structural key is signal-free, so it does not weaken the Step-8 no-leak property (Test C green).

Load-bearing MEASURED, five mutations all red: detach per-verdict keying · detach the fields
promote_verdict writes · make a partial/unparseable key tolerant · normalise the magnitude on write ·
remove the fallback (control — breaks the step1 suite at collection, proving the fallback bears load).

589 -> 597 tests. Full gate green (pytest, ruff, mypy).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QkjvTTxrg9LTrmghebfiij

README.md

@@ -141,6 +141,14 @@ when the seam is detached, so the loop cannot silently degrade into theater.
   silently ignoring the flag. Nothing about a flag-off run changes, and no savings claim depends
   on it.
 
+  A bundle may hold verdicts about **several candidates**, while its `validator-input.json`
+  describes only one. A `type: verdict` file therefore may declare its own retrieval key in
+  frontmatter — `affected_codes`, `measure_type`, `claimed_saving_nok` — and is keyed on that;
+  omit them and it falls back to the bundle's candidate, exactly as before. The three are **all or
+  nothing**: a partial declaration is refused rather than merged with the bundle candidate, since
+  the merge would produce a key belonging to neither. `promote_verdict` writes all three, so a
+  promoted verdict about one candidate never surfaces for another.
+
   The **prior-verdict fold — the learning step — happens only on the `--bundle-dir` path**; a
   plain `--docs-dir`-only run is single-shot (no fold). `--decision`/`--rationale` apply to the
   single-project path only and are inert in portfolio mode. **`--outbox-dir` must differ from