perf(relay): reduce encrypted binary traffic overhead (#2480)

Preserve application frame identity through encryption so negotiated binary traffic avoids base64 expansion while mixed-version peers remain compatible.

docs/architecture.md

@@ -141,6 +141,7 @@ Enables remote access when the daemon is behind a firewall.
 - The relay is zero-knowledge — it routes encrypted bytes and cannot read content
 - Client and daemon channels with identical API (`createClientChannel`, `createDaemonChannel`)
 - Pairing via QR code transfers the daemon's public key to the client
+- Optional E2EE capability negotiation preserves application frame kind: text plaintext uses base64 ciphertext text frames, while binary plaintext uses raw ciphertext binary frames; mixed-version peers remain base64-only
 - Self-hosted relays opt into TLS with `daemon.relay.useTls` or `PASEO_RELAY_USE_TLS=true`; the public (client-facing) TLS setting can be overridden independently via `daemon.relay.publicUseTls` or `PASEO_RELAY_PUBLIC_USE_TLS`
 
 The production relay server lives in [getpaseo/paseo-relay](https://github.com/getpaseo/paseo-relay). It is a distributed Elixir service. The Cloudflare relay implementation in this monorepo is retained as legacy code and is not deployed.

docs/terminal-performance.md

@@ -41,5 +41,5 @@ Terminal frames share the daemon main event loop with all agent traffic. The `ev
 ## Known remaining contention (follow-up candidates)
 
 - A single large `agent_stream` message (e.g. a 250KB diff payload) measurably delays terminal echo (~100ms-class dips) — cost is split between daemon serialization and app-side parse/render on the shared browser main thread.
-- Relay-attached clients pay pure-JS tweetnacl encryption + base64 per frame on the daemon main loop (`packages/relay/src/encrypted-channel.ts`).
+- Relay-attached clients pay pure-JS tweetnacl encryption on the daemon main loop (`packages/relay/src/encrypted-channel.ts`). Negotiated binary application frames stay binary ciphertext and avoid base64 encode/decode; text and mixed-version traffic remain base64 WebSocket text frames.
 - `sendToClient` re-stringifies session messages per socket; only matters for multi-socket connections.