A page on another origin can POST text/plain or a form without a CORS
preflight, so its visitors' browsers could store reports although the
server sends no CORS headers. decodeJSON now refuses a request whose
Content-Type is not application/json (parameters such as charset
allowed), and the report handler answers it 415 with the usual error
body, storing nothing. A JSON POST waits for the preflight, which only
an origin in CORS_ALLOWED_ORIGINS passes; the page already sends
application/json.
Model: opus-5-5
A report the buffer refuses now returns 500 instead of a false `ok`.
Reports reach disk later, so a failed disk write is still answered 200
and shows in the log, and at shutdown as a failed stop with a non-zero
exit. An over-limit body returns 413; malformed JSON stays 400. A
MaxBodyBytes middleware caps every route at 1 MiB; a route group can
only lower that limit. The raw geo blob is no longer logged; client_id,
timestamp and decode error text are cut to 128 bytes before logging.
Panic recovery logs the panic value and stack through slog.
Model: opus-5-5
Introduce the Go backend (netwatch-server) with an HTTP API that
accepts telemetry reports and persists them as zstd-compressed JSONL
files. Reports are buffered in memory and flushed to disk when the
buffer reaches 10 MiB or every 60 seconds.