fix(feedback): answer JSON on every path so failures stop reading as network errors

[forcingfx]

1. What: submitting the in-app feedback form failed with "Could not send
   feedback. Check your connection." — a message that points the user at their
   network when the network is fine. No feedback issue has been filed since
   2026-05-17.

2. Why: two defects that compound.

   The dialog called fetch and res.json() inside one try, so a failed
   parse was indistinguishable from a failed request. Any response that is
   not JSON — a crashed function's HTML 500, a gateway timeout page, a
   misrouted request — landed in the connection-error branch, discarding the
   status code that identifies which layer actually broke.

   The handler produced exactly such responses. body.message?.trim() ran
   straight off JSON.parse output, but null, arrays, bare strings, numbers
   and {"message": 42} are all valid JSON — each threw a TypeError out of the
   handler. A rejected handler promise is not a response, so the platform
   substitutes its own HTML error page. The method guard returned plain-text
   "Method not allowed" for the same reason: unparseable by the client.

   Neither had a smoke test or an E2E, so three months of silence went unseen.

3. Fix:

   • readTrimmedString narrows untrusted payload fields to string before use,
     keeping every malformed payload on the 400-JSON path. A non-string email
     is now treated as absent, matching the existing whitespace-email rule.
   • The method guard returns jsonResponse like every other branch.
   • submitFeedback separates transport from parsing: only a rejected fetch
     reports a connection problem; an answered request reports the server's own
     error, falling back to server error <status>.

4. Prevention:

   • Handler: a table-driven case per malformed payload asserting 400 JSON
     rather than a throw, plus the 405-is-JSON contract.
   • Dialog: an HTML 500 must surface the status and must NOT mention the
     connection; a failed submit keeps the dialog open with the text intact.
   • tests/smoke/feedback.test.ts exercises the live endpoint without filing
     an issue (every request is rejected at validation) and fails loudly if the
     GitHub credentials go missing — the check that was absent all along.
   • The JSON-on-every-path contract is recorded in docs/architecture.md and
     CLAUDE.md's Key Patterns.

   Verified in Chromium against the running app: HTML 500 → "server error 500",
   aborted request → "Check your connection.", 200 → success toast.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_012mG1HfKCGqPXXQ9m38W1aj

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Project	Deployment	Actions	Updated (UTC)
feedzero	Ready	Preview	Aug 18, 2026 5:18pm