group-translate: ctx.net.fetch has no .json() at runtime → translation silently fails

[rmyndharis]

Summary

group-translate calls res.json() on the result of ctx.net.fetch, but the sandbox runtime returns a plain object with no methods — so res.json() throws at runtime, the call fails-open, and translation is very likely a silent no-op in production.

Root cause

The host returns a serializable response and it crosses the worker boundary via structuredClone, which cannot carry functions. Traced in OpenWA core:

• performPluginFetch returns { ok, status, statusText, headers, body: string } — no .json()/.text()/.arrayBuffer() (src/core/plugins/plugin-net.ts).
• The worker capability client returns that result verbatim; there is no wrapper that re-adds the methods (src/core/plugins/sandbox/worker-capability.ts, worker-bootstrap.ts).

So at runtime ctx.net.fetch(...) resolves to { ok, status, statusText, headers, body }. res.json() is undefined → TypeError → caught by the client's try/catch → counted as a failure / returned empty.

The vendored type (types/openwa.d.ts) declared the method form (.json() etc.), which doesn't match the runtime — that's why this wasn't caught at compile time, and the unit tests pass only because they fake a .json()-bearing response (testing the mock, not the runtime shape).

Fix

• In group-translate/libretranslate.client.ts, read JSON.parse(res.body) instead of await res.json().
• Update the libretranslate.client.test.ts fakes to the real shape ({ ..., body: string }) so the test exercises reality.

(The vendored type was already corrected to expose body: string in #9.)

Verify

After the fix, a live round-trip against a real LibreTranslate instance should produce an actual translation (today it does not).