feat(policy-runtime): in-memory policy state with whispergate_policy tool and atomic persist

plugin/README.md

@@ -30,6 +30,7 @@ Optional:
 - `humanList` (default [])
 - `agentList` (default [])
 - `channelPoliciesFile` (per-channel overrides in a standalone JSON file)
+- `enableWhispergatePolicyTool` (default true)
 - `bypassUserIds` (deprecated alias of `humanList`)
 - `endSymbols` (default ["🔚"])
 - `enableDiscordControlTool` (default true)
@@ -39,6 +40,12 @@ Optional:
 
 Per-channel policy file example: `docs/channel-policies.example.json`.
 
+Policy file behavior:
+- loaded once on startup into memory
+- runtime decisions read memory state only
+- direct file edits do NOT affect memory state
+- `whispergate_policy` tool updates memory first, then persists to file (atomic write)
+
 ## Optional tool: `discord_control`
 
 This plugin now registers an optional tool named `discord_control`.