acp: Add support for slash commands (#37304)

Depends on
https://github.com/zed-industries/agent-client-protocol/pull/45

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Agus Zubiaga <agus@zed.dev>

crates/agent_servers/src/acp.rs

@@ -28,7 +28,7 @@ pub struct AcpConnection {
     connection: Rc<acp::ClientSideConnection>,
     sessions: Rc<RefCell<HashMap<acp::SessionId, AcpSession>>>,
     auth_methods: Vec<acp::AuthMethod>,
-    prompt_capabilities: acp::PromptCapabilities,
+    agent_capabilities: acp::AgentCapabilities,
     _io_task: Task<Result<()>>,
     _wait_task: Task<Result<()>>,
     _stderr_task: Task<Result<()>>,
@@ -148,7 +148,7 @@ impl AcpConnection {
             connection,
             server_name,
             sessions,
-            prompt_capabilities: response.agent_capabilities.prompt_capabilities,
+            agent_capabilities: response.agent_capabilities,
             _io_task: io_task,
             _wait_task: wait_task,
             _stderr_task: stderr_task,
@@ -156,7 +156,7 @@ impl AcpConnection {
     }
 
     pub fn prompt_capabilities(&self) -> &acp::PromptCapabilities {
-        &self.prompt_capabilities
+        &self.agent_capabilities.prompt_capabilities
     }
 }
 
@@ -223,7 +223,8 @@ impl AgentConnection for AcpConnection {
                     action_log,
                     session_id.clone(),
                     // ACP doesn't currently support per-session prompt capabilities or changing capabilities dynamically.
-                    watch::Receiver::constant(self.prompt_capabilities),
+                    watch::Receiver::constant(self.agent_capabilities.prompt_capabilities),
+                    response.available_commands,
                     cx,
                 )
             })?;