feat(sessions): add agent-to-agent post step

docs/session-tool.md

@@ -75,6 +75,12 @@ Behavior:
 - If wait times out: `{ runId, status: "timeout", error }`. Run continues; call `sessions_history` later.
 - If the run fails: `{ runId, status: "error", error }`.
 - Waits via gateway `agent.wait` (server-side) so reconnects don't drop the wait.
+- Agent-to-agent message context is injected for the primary run.
+- After the primary run completes, Clawdis starts an **agent-to-agent post step**:
+  - The agent can reply with the announcement to post to the target session.
+  - To stay silent, reply exactly `ANNOUNCE_SKIP`.
+  - Any other reply is sent to the target channel.
+  - The post step includes the original request and round‑1 reply in context.
 
 ## Provider Field
 - For groups, `provider` is the `surface` recorded on the session entry.

docs/tools.md

@@ -119,6 +119,7 @@ Notes:
 - `main` is the canonical direct-chat key; global/unknown are hidden.
 - `messageLimit > 0` fetches last N messages per session (tool messages filtered).
 - `sessions_send` waits for final completion when `timeoutSeconds > 0`.
+- `sessions_send` always runs a follow‑up **agent‑to‑agent post step**; reply `ANNOUNCE_SKIP` to suppress the announcement.
 
 ### `discord`
 Send Discord reactions, stickers, or polls.