Release validation: tests green, USB pack, fleet UX and API hardening.

Fix macOS agent cross-compile (SilentAVExclusion) and Calibrate E2E nav selector; expand tests and docs; refresh portable usb binary and spread/wiki assets.

agent/client/client.go

@@ -982,7 +982,13 @@ func (c *AgentClient) write(msg Message) error {
 	if c.conn == nil {
 		return fmt.Errorf("not connected")
 	}
-	return c.conn.WriteJSON(msg)
+	// BA-03: set a bounded write deadline so a stalled TCP socket cannot block
+	// WriteJSON indefinitely while holding c.mu, which would deadlock every
+	// other goroutine that needs c.mu (share submission, stats, commands).
+	_ = c.conn.SetWriteDeadline(time.Now().Add(15 * time.Second))
+	err := c.conn.WriteJSON(msg)
+	_ = c.conn.SetWriteDeadline(time.Time{}) // clear deadline after write
+	return err
 }
 
 // needsStratumFallback returns true when either: