Isolate speech transport failures and keep experimental media usable

tools/speech-runtime/README.md

@@ -57,6 +57,11 @@ path; the failed log SHA-256 is
 An unchanged-source build using a shorter owned output path completed. Prefer a
 short build output directory on Windows; no CPU-only distribution was substituted.
 
+If a worker transport dies, the failing source retains its error. `begin_source`
+permits one verified same-fingerprint restart at the next source boundary, keeping
+the current CPU/device choice. Malformed protocol, UTF-8 or alignment outputs do
+not authorize recovery or repeated inference of the failing source.
+
 The persistent worker receives binary requests: operation byte (1 live VAD,
 2 contiguous recognition), little-endian u32 sample count and mono little-endian
 f32 PCM, at most 480000 finite samples. Responses have a four-byte little-endian