fix(acp): advertise slash commands via ACP protocol

Send AvailableCommandsUpdate on session create/load/resume/fork so ACP
clients (Zed, etc.) can discover /help, /model, /tools, /compact, etc.
Also rewrites /compact to use agent._compress_context() properly with
token estimation and session DB isolation.

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

acp_adapter/server.py

@@ -13,6 +13,8 @@ from acp.schema import (
     AgentCapabilities,
     AuthenticateResponse,
     AuthMethodAgent,
+    AvailableCommand,
+    AvailableCommandsUpdate,
     ClientCapabilities,
     EmbeddedResourceContentBlock,
     ForkSessionResponse,
@@ -37,6 +39,7 @@ from acp.schema import (
     SessionListCapabilities,
     SessionInfo,
     TextContentBlock,
+    UnstructuredCommandInput,
     Usage,
 )
 
@@ -84,6 +87,48 @@ def _extract_text(
 class HermesACPAgent(acp.Agent):
     """ACP Agent implementation wrapping Hermes AIAgent."""
 
+    _SLASH_COMMANDS = {
+        "help": "Show available commands",
+        "model": "Show or change current model",
+        "tools": "List available tools",
+        "context": "Show conversation context info",
+        "reset": "Clear conversation history",
+        "compact": "Compress conversation context",
+        "version": "Show Hermes version",
+    }
+
+    _ADVERTISED_COMMANDS = (
+        {
+            "name": "help",
+            "description": "List available commands",
+        },
+        {
+            "name": "model",
+            "description": "Show current model and provider, or switch models",
+            "input_hint": "model name to switch to",
+        },
+        {
+            "name": "tools",
+            "description": "List available tools with descriptions",
+        },
+        {
+            "name": "context",
+            "description": "Show conversation message counts by role",
+        },
+        {
+            "name": "reset",
+            "description": "Clear conversation history",
+        },
+        {
+            "name": "compact",
+            "description": "Compress conversation context",
+        },
+        {
+            "name": "version",
+            "description": "Show Hermes version",
+        },
+    )
+
     def __init__(self, session_manager: SessionManager | None = None):
         super().__init__()
         self.session_manager = session_manager or SessionManager()
@@ -219,6 +264,7 @@ class HermesACPAgent(acp.Agent):
         state = self.session_manager.create_session(cwd=cwd)
         await self._register_session_mcp_servers(state, mcp_servers)
         logger.info("New session %s (cwd=%s)", state.session_id, cwd)
+        self._schedule_available_commands_update(state.session_id)
         return NewSessionResponse(session_id=state.session_id)
 
     async def load_session(
@@ -234,6 +280,7 @@ class HermesACPAgent(acp.Agent):
             return None
         await self._register_session_mcp_servers(state, mcp_servers)
         logger.info("Loaded session %s", session_id)
+        self._schedule_available_commands_update(session_id)
         return LoadSessionResponse()
 
     async def resume_session(
@@ -249,6 +296,7 @@ class HermesACPAgent(acp.Agent):
             state = self.session_manager.create_session(cwd=cwd)
         await self._register_session_mcp_servers(state, mcp_servers)
         logger.info("Resumed session %s", state.session_id)
+        self._schedule_available_commands_update(state.session_id)
         return ResumeSessionResponse()
 
     async def cancel(self, session_id: str, **kwargs: Any) -> None:
@@ -274,6 +322,8 @@ class HermesACPAgent(acp.Agent):
         if state is not None:
             await self._register_session_mcp_servers(state, mcp_servers)
         logger.info("Forked session %s -> %s", session_id, new_id)
+        if new_id:
+            self._schedule_available_commands_update(new_id)
         return ForkSessionResponse(session_id=new_id)
 
     async def list_sessions(
@@ -411,15 +461,50 @@ class HermesACPAgent(acp.Agent):
 
     # ---- Slash commands (headless) -------------------------------------------
 
-    _SLASH_COMMANDS = {
-        "help": "Show available commands",
-        "model": "Show or change current model",
-        "tools": "List available tools",
-        "context": "Show conversation context info",
-        "reset": "Clear conversation history",
-        "compact": "Compress conversation context",
-        "version": "Show Hermes version",
-    }
+    @classmethod
+    def _available_commands(cls) -> list[AvailableCommand]:
+        commands: list[AvailableCommand] = []
+        for spec in cls._ADVERTISED_COMMANDS:
+            input_hint = spec.get("input_hint")
+            commands.append(
+                AvailableCommand(
+                    name=spec["name"],
+                    description=spec["description"],
+                    input=UnstructuredCommandInput(hint=input_hint)
+                    if input_hint
+                    else None,
+                )
+            )
+        return commands
+
+    async def _send_available_commands_update(self, session_id: str) -> None:
+        """Advertise supported slash commands to the connected ACP client."""
+        if not self._conn:
+            return
+
+        try:
+            await self._conn.session_update(
+                session_id=session_id,
+                update=AvailableCommandsUpdate(
+                    sessionUpdate="available_commands_update",
+                    availableCommands=self._available_commands(),
+                ),
+            )
+        except Exception:
+            logger.warning(
+                "Failed to advertise ACP slash commands for session %s",
+                session_id,
+                exc_info=True,
+            )
+
+    def _schedule_available_commands_update(self, session_id: str) -> None:
+        """Send the command advertisement after the session response is queued."""
+        if not self._conn:
+            return
+        loop = asyncio.get_running_loop()
+        loop.call_soon(
+            asyncio.create_task, self._send_available_commands_update(session_id)
+        )
 
     def _handle_slash_command(self, text: str, state: SessionState) -> str | None:
         """Dispatch a slash command and return the response text.
@@ -539,11 +624,39 @@ class HermesACPAgent(acp.Agent):
             return "Nothing to compress — conversation is empty."
         try:
             agent = state.agent
-            if hasattr(agent, "compress_context"):
-                agent.compress_context(state.history)
-                self.session_manager.save_session(state.session_id)
-                return f"Context compressed. Messages: {len(state.history)}"
-            return "Context compression not available for this agent."
+            if not getattr(agent, "compression_enabled", True):
+                return "Context compression is disabled for this agent."
+            if not hasattr(agent, "_compress_context"):
+                return "Context compression not available for this agent."
+
+            from agent.model_metadata import estimate_messages_tokens_rough
+
+            original_count = len(state.history)
+            approx_tokens = estimate_messages_tokens_rough(state.history)
+            original_session_db = getattr(agent, "_session_db", None)
+
+            try:
+                # ACP sessions must keep a stable session id, so avoid the
+                # SQLite session-splitting side effect inside _compress_context.
+                agent._session_db = None
+                compressed, _ = agent._compress_context(
+                    state.history,
+                    getattr(agent, "_cached_system_prompt", "") or "",
+                    approx_tokens=approx_tokens,
+                    task_id=state.session_id,
+                )
+            finally:
+                agent._session_db = original_session_db
+
+            state.history = compressed
+            self.session_manager.save_session(state.session_id)
+
+            new_count = len(state.history)
+            new_tokens = estimate_messages_tokens_rough(state.history)
+            return (
+                f"Context compressed: {original_count} -> {new_count} messages\n"
+                f"~{approx_tokens:,} -> ~{new_tokens:,} tokens"
+            )
         except Exception as e:
             return f"Compression failed: {e}"