feat(session): add dmScope for multi-user DM isolation

Co-authored-by: Alphonse-arianee <Alphonse-arianee@users.noreply.github.com>

docs/gateway/configuration.md

@@ -2261,6 +2261,7 @@ Controls session scoping, idle expiry, reset triggers, and where the session sto
 {
   session: {
     scope: "per-sender",
+    dmScope: "main",
     idleMinutes: 60,
     resetTriggers: ["/new", "/reset"],
     // Default is already per-agent under ~/.clawdbot/agents/<agentId>/sessions/sessions.json
@@ -2285,6 +2286,10 @@ Controls session scoping, idle expiry, reset triggers, and where the session sto
 Fields:
 - `mainKey`: direct-chat bucket key (default: `"main"`). Useful when you want to “rename” the primary DM thread without changing `agentId`.
   - Sandbox note: `agents.defaults.sandbox.mode: "non-main"` uses this key to detect the main session. Any session key that does not match `mainKey` (groups/channels) is sandboxed.
+- `dmScope`: how DM sessions are grouped (default: `"main"`).
+  - `main`: all DMs share the main session for continuity.
+  - `per-peer`: isolate DMs by sender id across channels.
+  - `per-channel-peer`: isolate DMs per channel + sender (recommended for multi-user inboxes).
 - `agentToAgent.maxPingPongTurns`: max reply-back turns between requester/target (0–5, default 5).
 - `sendPolicy.default`: `allow` or `deny` fallback when no rule matches.
 - `sendPolicy.rules[]`: match by `channel`, `chatType` (`direct|group|room`), or `keyPrefix` (e.g. `cron:`). First deny wins; otherwise allow.

docs/gateway/security.md

@@ -123,6 +123,18 @@ clawdbot pairing approve <channel> <code>
 
 Details + files on disk: [Pairing](/start/pairing)
 
+## DM session isolation (multi-user mode)
+
+By default, Clawdbot routes **all DMs into the main session** so your assistant has continuity across devices and channels. If **multiple people** can DM the bot (open DMs or a multi-person allowlist), consider isolating DM sessions:
+
+```json5
+{
+  session: { dmScope: "per-channel-peer" }
+}
+```
+
+This prevents cross-user context leakage while keeping group chats isolated. See [Session Management](/concepts/session) and [Configuration](/gateway/configuration).
+
 ## Allowlists (DM + groups) — terminology
 
 Clawdbot has two separate “who can trigger me?” layers: