message editor: Only allow types of content the agent can handle (#36616)

Uses the new
[`acp::PromptCapabilities`](a39b7f635d/rust/agent.rs (L194-L215))
to disable non-file mentions and images for agents that don't support
them.

Release Notes:

- N/A

crates/agent_servers/src/acp/v0.rs

@@ -498,6 +498,14 @@ impl AgentConnection for AcpConnection {
         })
     }
 
+    fn prompt_capabilities(&self) -> acp::PromptCapabilities {
+        acp::PromptCapabilities {
+            image: false,
+            audio: false,
+            embedded_context: false,
+        }
+    }
+
     fn cancel(&self, _session_id: &acp::SessionId, cx: &mut App) {
         let task = self
             .connection

crates/agent_servers/src/acp/v1.rs

@@ -21,6 +21,7 @@ pub struct AcpConnection {
     connection: Rc<acp::ClientSideConnection>,
     sessions: Rc<RefCell<HashMap<acp::SessionId, AcpSession>>>,
     auth_methods: Vec<acp::AuthMethod>,
+    prompt_capabilities: acp::PromptCapabilities,
     _io_task: Task<Result<()>>,
 }
 
@@ -119,6 +120,7 @@ impl AcpConnection {
             connection: connection.into(),
             server_name,
             sessions,
+            prompt_capabilities: response.agent_capabilities.prompt_capabilities,
             _io_task: io_task,
         })
     }
@@ -206,6 +208,10 @@ impl AgentConnection for AcpConnection {
         })
     }
 
+    fn prompt_capabilities(&self) -> acp::PromptCapabilities {
+        self.prompt_capabilities
+    }
+
     fn cancel(&self, session_id: &acp::SessionId, cx: &mut App) {
         let conn = self.connection.clone();
         let params = acp::CancelNotification {

crates/agent_servers/src/claude.rs

@@ -319,6 +319,14 @@ impl AgentConnection for ClaudeAgentConnection {
         cx.foreground_executor().spawn(async move { end_rx.await? })
     }
 
+    fn prompt_capabilities(&self) -> acp::PromptCapabilities {
+        acp::PromptCapabilities {
+            image: true,
+            audio: false,
+            embedded_context: true,
+        }
+    }
+
     fn cancel(&self, session_id: &acp::SessionId, _cx: &mut App) {
         let sessions = self.sessions.borrow();
         let Some(session) = sessions.get(session_id) else {