Share the apiClient error-message helper across the feedback surface

[CodeGhost21]

Use a concise sentence-case title that describes the work item.

Summary

Lift messageForApiError out of FeedbackSubmitForm.tsx into a shared helper and converge the four other feedback call sites on it, so a server-supplied error message reaches the user instead of being replaced by generic copy.

Problem / Context

apiClient rejects with a plain { success: false, error: "..." } object, not an Error (app/src/services/apiClient.ts:109-111,126,130). Every err instanceof Error ? err.message : t(...) against it therefore takes the fallback branch unconditionally — the server's message is discarded 100% of the time, and the user is told "Something went wrong. Please try again." when the backend explained exactly what was wrong.

#5431 fixed this for the submit form with a file-local messageForApiError, which matters there because the backend quality gate returns the reason a draft was refused. The same pattern is still live at four more sites on the same surface, all going through the same apiClient:

• app/src/components/feedback/FeedbackComments.tsx:56 — comment load
• app/src/components/feedback/FeedbackComments.tsx:78 — comment post
• app/src/components/feedback/FeedbackAdminMenu.tsx:42 — admin status update
• app/src/pages/Feedback.tsx:82 — board load

Raised in review on #5431 and deliberately left out of that PR as scope. Left alone, each site grows its own copy of the fix.

Scope (optional)

In scope: a single exported helper (services-level, next to apiClient, since the shape it decodes is apiClient's), the four call sites above, and unit coverage for both rejection shapes.

Not in scope: changing what apiClient throws. Making it reject with a real Error would be the deeper fix, but it is a cross-cutting change to every consumer in the app, not a feedback-surface cleanup — worth its own issue if wanted.

Note the helper must keep the fallback for a blank or missing error field, and must not surface a raw payload dump — only the error string.

Acceptance criteria

• Shared helper — messageForApiError(err, fallback) lives in one place, handles the Error shape, the { success, error } shape, and falls back on a blank or absent message.
• Call sites converged — the four sites above and FeedbackSubmitForm.tsx use it; no instanceof Error check against an apiClient rejection remains on the feedback surface.
• Tests — unit coverage for all three branches, plus at least one component test proving a server message reaches the screen at a converged site.
• Diff coverage ≥ 80% — the implementing PR meets the changed-lines coverage gate (Vitest + cargo-llvm-cov, enforced by .github/workflows/ci-lite.yml) when code changes are involved.

Related

• Surface the feedback quality tier in the composer #5431 — where the bug was diagnosed and fixed for the submit form; review thread flagging the other four sites
• Surface the feedback quality tier in the composer #5430 — the composer quality-tier issue Surface the feedback quality tier in the composer #5431 closes