docs: add unified session configuration to README for cross-channel continuity

README.md

@@ -1519,6 +1519,32 @@ Common examples: `UTC`, `America/New_York`, `America/Los_Angeles`, `Europe/Londo
 
 > Need another timezone? Browse the full [IANA Time Zone Database](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones).
 
+### Unified Session
+
+By default, each channel × chat ID combination gets its own session. If you use nanobot across multiple channels (e.g. Telegram + Discord + CLI) and want them to share the same conversation, enable `unifiedSession`:
+
+```json
+{
+  "agents": {
+    "defaults": {
+      "unifiedSession": true
+    }
+  }
+}
+```
+
+When enabled, all incoming messages — regardless of which channel they arrive on — are routed into a single shared session. Switching from Telegram to Discord (or any other channel) continues the same conversation seamlessly.
+
+| Behavior | `false` (default) | `true` |
+|----------|-------------------|--------|
+| Session key | `channel:chat_id` | `unified:default` |
+| Cross-channel continuity | No | Yes |
+| `/new` clears | Current channel session | Shared session |
+| `/stop` finds tasks | By channel session | By shared session |
+| Existing `session_key_override` (e.g. Telegram thread) | Respected | Still respected — not overwritten |
+
+> This is designed for single-user, multi-device setups. It is **off by default** — existing users see zero behavior change.
+
 ## 🧩 Multiple Instances
 
 Run multiple nanobot instances simultaneously with separate configs and runtime data. Use `--config` as the main entrypoint. Optionally pass `--workspace` during `onboard` when you want to initialize or update the saved workspace for a specific instance.