Extract the pure Perplexity wire protocol (consts, SSE stream types, SSE parsing,
OpenAI<->Perplexity message translation, request/query builders, content extraction,
sseChunk) verbatim into the leaf perplexity-web/protocol.ts. Host imports back the 10
symbols it uses; everything module-private (no re-export). Session cache, TLS fetch,
auth, and the executor class stay in the host.
Host 1028 -> 534 LOC. Byte-identical bodies (verbatim), leaf imports only randomUUID
(no host import, no cycle). Adds a split-guard; consumer tests stay green
(perplexity-web 26, streaming-tools-5927 2, tls-client 6, key-validation-models 2).
