fix(workdir): keep diagnostic context transparent to Write creation

docs/development/workdir-refusal-diagnostics.md

@@ -131,6 +131,12 @@ is never parsed into a reason.
   18 codes with no reason, a typed reason, and nested diagnostic wrappers. In
   particular, OutcomeUnknown/Conflict remain execution failures with unchanged
   display and inspection-before-retry guidance, not argument errors.
+  Operational consumers share `WorkdirError::classification_source` to ignore
+  only diagnostic wrappers while retaining the original error for diagnostics.
+  Public Write tests cross JSON stat errors into the tool and the checked local
+  provider: missing files are created identically without/with/nested reasons;
+  denied/read-only/conflict/unknown-outcome stat failures never write or retry.
+  This protects actual create control flow in addition to error conversion.
 - A signed real self-handler test observes command dispatch, then removes only
   its fixture session-registration entry before returning the start handle.
   The 502 remains a post-start `command_registration` failure with a neutral

docs/report/t731-review-verdict-registration-401.md

@@ -25,8 +25,8 @@
 
 ## Handling and limitation
 
-The finding is being fixed in a forward commit on the same source ref. Source
-movement requires a fresh exact-source trusted review. The original narrative
+The first finding was fixed in forward commit `10c55874` on the same source ref.
+Source movement requires a fresh exact-source trusted review. The original narrative
 verdict is not substituted for a recorded authoritative review event.
 
 Ticket seq4 records this operational blocker for Orchestrator attention. The
@@ -40,6 +40,34 @@ reported Workdir 403, and T-731's fixture diagnostics do not resolve either live
 incident. The registration failure is not repaired by the product-code changes
 in this Ticket.
 
+## Fresh review: invalid severity rejected (422)
+
+- Reviewed source after the first forward fix:
+  `10c55874e3cc4c3562f608e10c56ff1c4c2a4d3c`.
+- Fresh request: MR seq3 event `01a120f4-6c90-7791-a36f-69d52e2cbd4b`,
+  `2026-10-09T13:57:31.897275884+00:00`, same Ticket revision and sole MR.
+- Independent review found a second operational regression: normal Write's
+  bare NotFound match failed to create files for typed/nested diagnostic context.
+  A public-tool harness reproduced it despite 59 focused tests passing.
+- The sole executed verdict attempt returned HTTP 422, specifically invalid
+  `findings[0].severity = medium`; Backend expects blocker/major/minor/note.
+  Committed response: `E01a120fc-a7b7-79c3-b812-12cfd1038f75`.
+- Observed UTC bracket was 14:05:37.641361776Z–14:06:36.777627982Z on
+  2026-10-09, not the exact server request timestamp. Parent MR reread at
+  14:11:31Z still had no events after seq3.
+- Parent requested a schema-only correction on the unchanged snapshot, but the
+  Reviewer role's exactly-once instruction disallowed a second verdict call.
+  Its committed follow-up confirms no corrected submission executed. No other
+  mutation path or Reviewer was used to bypass this restriction.
+
+This 422 is input validation evidence, not proof that the earlier 401 has been
+resolved. The narrative request-changes judgment is not a recorded verdict.
+The reproduced second regression is addressed by the shared classification
+source and real Write regression in this forward change on the existing branch.
+The new test fails for the typed-reason case before the fix and passes all three
+forms after it. That source movement still needs fresh exact-source review, not
+reuse of the old review binding. The user-reported Workdir 403 remains unidentified.
+
 ## Improvement proposal
 
 A verdict-registration rejection should expose a safe, bounded internal
@@ -49,3 +77,8 @@ locate the corresponding Backend record. The current bare 401 leaves the
 reviewer unable to distinguish authentication failure from downstream authority
 rejection. Investigate under separate authorization; do not weaken the guarded
 review path or retry blindly to hide the failure.
+
+Also align the tool schema's severity vocabulary with the Backend enum, rather
+than advertising an unconstrained string that consumes an exactly-once verdict
+attempt on a deterministic 422. Any correction/review-grant lifecycle policy
+needs a separate explicit design; this Ticket does not change it.