fix(mobile): give a direct handshake as long as the desktop allows it (#36864)

The phone gave a direct socket 5 s from open to authenticated, while
the desktop keeps an unauthenticated socket for 10 s. On a slow link
(a handshake is two round trips, so ~2.5 s RTT is enough) the phone
dropped the socket the desktop would have accepted, then redialed into
the same deadline forever: the 'Can't connect' loop a test documented.

Both ends now share PAIRED_E2EE_HANDSHAKE_DEADLINE_MS (10 s). A link
that needs 6 s to authenticate now connects on the first dial; one that
never authenticates still escalates the same way, 5 s later. Relay
dials are unaffected: they keep their own stage budgets and race the
direct dial after 2.5 s.

src/main/runtime/rpc/e2ee-channel.ts

@@ -1,5 +1,6 @@
 // Keep E2EE framing outside transport-independent plaintext RPC handlers.
 import type { WebSocket } from 'ws'
+import { PAIRED_E2EE_HANDSHAKE_DEADLINE_MS } from '../../../shared/paired-e2ee-handshake-deadline'
 import { deriveSharedKey, encrypt, decrypt, decryptBytes } from '../../../shared/e2ee-crypto'
 import {
   DesktopMobileE2EEV2Session,
@@ -30,7 +31,6 @@ import type {
 } from './rpc-binary-sender'
 import type { DevicePrincipal } from '../device-principal'
 
-const HANDSHAKE_TIMEOUT_MS = 10_000
 const MAX_CONSECUTIVE_DECRYPT_FAILURES = 5
 
 export type E2EEChannelOptions = {
@@ -104,7 +104,7 @@ export class E2EEChannel {
 
     this.handshakeTimer = setTimeout(() => {
       this.onError(4002, 'E2EE handshake timeout')
-    }, HANDSHAKE_TIMEOUT_MS)
+    }, PAIRED_E2EE_HANDSHAKE_DEADLINE_MS)
   }
 
   onMessage(

src/shared/paired-e2ee-handshake-deadline.ts

@@ -0,0 +1,6 @@
+/**
+ * How long a paired socket may take from open to authenticated, on both ends. The desktop closes a
+ * socket that has not authenticated by then, so a phone that gives up sooner drops slow links the
+ * desktop would still have accepted.
+ */
+export const PAIRED_E2EE_HANDSHAKE_DEADLINE_MS = 10_000