feat(host-agent): Phase 1b RCON — WebRCON (rust) + Source RCON (conan/soulmask)

rcon func on the instance command channel: WebSocket JSON WebRCON with
Identifier correlation (skips chat/log noise frames) and full Valve
Source RCON over TCP (auth, exec, multi-packet reassembly via empty
probe, 1MiB cap). Protocol inferred from game, explicit kind override
in [instance.rcon]. Always 127.0.0.1 — agent is co-located.

Hardening from review: WebRCON password never interpolated into error
contexts/logs (redacted URL); probe-tolerant termination — a quiet
period after received data ends the response for servers that don't
echo the probe (Soulmask conformance unverified), so data is never
discarded on probe timeout.

13/13 tests green incl. mock Source-RCON server (auth/multi-packet/
errors) and mock WebRCON server (noise-frame skipping).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

corrosion-host-agent/src/config.rs

@@ -10,6 +10,8 @@ use serde::Deserialize;
 use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 
+use crate::rcon::RconConfig;
+
 /// Instance ids share the NATS subject namespace with host-level segments.
 const RESERVED_INSTANCE_IDS: &[&str] = &["host", "cmd", "files", "update", "agent"];
 
@@ -59,6 +61,10 @@ pub struct InstanceConfig {
     /// Working directory for the process. Defaults to the executable's directory.
     #[serde(default)]
     pub working_dir: Option<PathBuf>,
+    /// RCON connection settings for this instance.  Absent = rcon unavailable.
+    /// Protocol defaults to WebRcon for rust, Source for conan/soulmask.
+    #[serde(default)]
+    pub rcon: Option<RconConfig>,
 }
 
 impl InstanceConfig {