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/agent.example.toml

@@ -23,11 +23,28 @@ game = "rust"          # rust | conan | soulmask | dune
 root = "/opt/rustserver"
 label = "Main 2x Vanilla"
 
+# RCON lets the panel send console commands to the running server.
+# For rust the protocol is WebRCON (WebSocket JSON); for conan/soulmask it is
+# Source RCON (Valve TCP binary). `kind` is optional — it is inferred from
+# the game name when absent.
+#
+# The [instance.rcon] sub-table MUST immediately follow the [[instance]] entry
+# it belongs to (standard TOML array-of-tables scoping rule).
+[instance.rcon]
+port = 28016
+password = "changeme"
+# kind = "webrcon"   # explicit override; omit to infer from game
+
 # [[instance]]
 # id = "soulmask-main"
 # game = "soulmask"
 # root = "/opt/soulmask/main"
 # label = "Cloud Mist Forest (cluster main)"
+#
+# [instance.rcon]
+# port = 19000
+# password = "changeme"
+# # kind = "source"  # inferred automatically for soulmask
 
 [prober]
 interval_seconds = 300