Unknown /api paths returned the SPA with HTTP 200

An authenticated GET to any unrecognised API route — a typo, a renamed
endpoint, an older client — fell through to the SPA fallback and returned
200 text/html containing the app shell.

This is close to the worst failure shape for an API consumer. `response.ok` is
true, so nothing treats it as an error; the caller then dies on `JSON.parse`
with "Unexpected token '<'" far from the actual cause. The MCP server, the CLI
and Piggy all consume this API and would all have hit it. It was masked from
casual testing because unauthenticated requests are rejected earlier by the
auth middleware, so it only appears once you hold a valid token.

Found by probing production with Scott's token: GET /api/keys (the real path is
/api/api-keys) returned 200 text/html.

The static-file middleware already carried this guard — added for the same
reason when og.png was being served as HTML — but the SPA fallback beneath it
did not. Same guard, one place missing.

Verified: unknown API paths now return 404 application/json, real API paths
still answer, client-side routes still receive the shell, and static assets
still serve with their own content types. Typecheck clean, 124 unit tests and
the e2e suite green.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -165,6 +165,13 @@ Verified: 1× A100 at 1.79, 2× A100 at 3.58. `gpuMemory` is likewise a node
 total. There is an open bug for this — the mapper currently stores both as if
 per-GPU, so an 8-GPU node reads eight times too expensive.
 
+**The SPA fallback must never answer an `/api/` path.** Without an explicit
+guard, an unknown API route returns `200 text/html` — the app shell — and the
+caller sees `response.ok === true` before failing on `JSON.parse` with
+"Unexpected token '<'", a long way from the cause. Both the static-file
+middleware and the SPA fallback in `apps/api/src/server.ts` carry the guard;
+anything added after them needs it too.
+
 **Prime Intellect has two API hosts.** `api.primeintellect.ai` is compute and
 pods. Inference is `api.pinference.ai/api/v1`, OpenAI-compatible.