Three pieces:
- src/lib/download.ts: generic downloadTextFile(filename, mime, text)
helper. Mirrors csv.ts:downloadCsv but takes an explicit MIME type and
drops the BOM prepend (which would corrupt the ISA segment).
- src/lib/api.ts: serializeClaim837(id) → {text, filename}. Fetches
GET /api/claims/{id}/serialize-837, pulls the suggested filename from
Content-Disposition (falls back to claim-{id}.x12 if the header is
missing). Throws ApiError on non-2xx so callers can branch on .status.
- ClaimDrawerHeader: Download icon button between the amount and the
close button. Click → api.serializeClaim837 → downloadTextFile.
Disabled + 'Downloading 837 file' aria-label while the fetch is in
flight so the click feels responsive. Optional onError prop surfaces
fetch failures; defaults to a no-op so existing callers stay clean.
Tests: 3 download.test.ts, 3 api.test.ts, 2 header.test.ts (happy
path + error path). Frontend: 350 passing (+8 from 342).
- RawSegmentsPanel: summary now reads 'Show N raw segments' for
non-empty (with singular pluralization). The previous identical
ternary branches read as a bug.
- PartiesGrid: replace the verbose intersection cast on AddressBlock
with a direct ClaimDetailAddress cast (the union's other arm is
Record<string, never>, ruled out by isEmptyAddress above).
ClaimDrawerError.tsx already wraps its error surface with role=alert
(line 36). Apply the same pattern to the ValidationPanel errors
sub-section so assistive tech announces blocking validation failures
when the drawer opens, matching the established sibling pattern.
Warnings stay decorative (no role change) — they're advisories, not
blocks.
The parametrized variant test only exercised 4 of the 6 mapped states
(submitted/denied/paid/pending). Add accepted (-> default) and matched
(-> success) so the entire STATE_VARIANT map is verified, not just the
branches whose tokens happened to be easy to reach.
Tyler