The Android build always talks to the Pi cross-origin -- a Capacitor
webview serves the app from http://localhost, not from your domain -- so
the browser sends a preflight OPTIONS first. It is not permitted to attach
an Authorization header to that. Auth ran before anything else, so the
preflight came back 401 and the real request was never attempted.
There were no Access-Control-Allow-* headers either, so even a successful
preflight would not have helped. Verified from an actual page before the
fix: GET /api/sync and POST /api/tutor both "Failed to fetch" -- an opaque
network error that points at the network rather than at middleware order.
CORS now runs first and answers OPTIONS itself. Any origin is allowed by
default, which is not a hole: the gate is a bearer token rather than a
cookie, so a hostile page gains nothing from being allowed to send a
request it cannot authenticate. HANKAN_ALLOWED_ORIGINS narrows it.
backends/echo.ts is a keyless backend that reflects the request back in
chunks. Deploying involves a container, a reverse proxy, a token, CORS and
an SSE stream that has to survive compression -- five things that break
independently, none of which involve Anthropic. HANKAN_TUTOR_BACKEND=echo
proves all five from the phone before a key exists and before anything is
billed. CI now runs the server that way, so the tutor endpoint is
exercised over real HTTP rather than only against an injected mock.
test/server/http.test.ts covers the preflight, the allow-origin header on
real responses, Vary: Origin, that a bad token is still refused, and that
the SSE stream parses and terminates with a done event.
Verified end to end in a browser: the Pi configured through the settings
panel, sync pushing 2 rows and a second sync moving 0 (the pushedAt
watermark holding), the header switching from "local stand-in" to
"connected", and a turn streaming back over SSE with the 8,859-character
system prompt intact.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
POST /api/tutor takes the assembled system prompt, the transcript the
client owns, and the new message, and streams tokens back. It holds
nothing between requests, so a dropped connection costs one turn rather
than the conversation.
The seam moved first: Sample took the assembled prompt as messages[0] with
role user. It now has an explicit system field, which is what lets the
backend put it in the API's system parameter as a cached block. The gate
is ~12k characters and is byte-identical for as long as the learner stays
in one unit, so every turn after the first reads the prefix at a fraction
of the input price. That is the single biggest cost lever in the design,
and it was unreachable through the old shape.
prompt/tutor-system.md still ships unchanged; only where the string is
placed changed.
SSE has three rules that are silent when broken, and all three are
handled: every event ends with a blank line, payloads are JSON-encoded
because a raw newline in Korean text would break the framing, and a `:`
heartbeat every 15s keeps intermediaries from timing the stream out.
Cache-Control is set on the returned Response rather than inside
streamSSE, which writes its own and would overwrite it; `no-transform` is
there because compression, not buffering, is what usually makes SSE look
like it hangs behind a proxy.
The client uses fetch + getReader, not EventSource — EventSource cannot
POST, and the body is {system, history, message}. Aborting closes the
connection, the server aborts upstream, and a cancelled turn stops
billing. With no server configured the app falls back to the stub, so the
offline build is untouched.
backends/anthropic.ts is the default. backends/agent-sdk.ts is deliberately
unimplemented and documents why the plain API was chosen over PORT.md's
Agent SDK — chiefly that its prompt accepts only user-role messages, so
the transcript would have to be flattened into a single turn.
The endpoint's own tests use a mock backend and need no API key.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
