acp: Support session modes (e.g. CC plan mode) (#37632)

Adds support for [ACP session
modes](https://github.com/zed-industries/agent-client-protocol/pull/67)
enabling plan and other permission modes in CC:


https://github.com/user-attachments/assets/dea18d82-4da6-465e-983b-02b77c6dcf15


Release Notes:

- Claude Code: Add support for plan mode, and all other permission modes

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/acp_thread/src/acp_thread.rs

@@ -805,6 +805,7 @@ pub enum AcpThreadEvent {
     PromptCapabilitiesUpdated,
     Refusal,
     AvailableCommandsUpdated(Vec<acp::AvailableCommand>),
+    ModeUpdated(acp::SessionModeId),
 }
 
 impl EventEmitter<AcpThreadEvent> for AcpThread {}
@@ -1007,6 +1008,9 @@ impl AcpThread {
             acp::SessionUpdate::AvailableCommandsUpdate { available_commands } => {
                 cx.emit(AcpThreadEvent::AvailableCommandsUpdated(available_commands))
             }
+            acp::SessionUpdate::CurrentModeUpdate { current_mode_id } => {
+                cx.emit(AcpThreadEvent::ModeUpdated(current_mode_id))
+            }
         }
         Ok(())
     }
@@ -1303,11 +1307,12 @@ impl AcpThread {
         &mut self,
         tool_call: acp::ToolCallUpdate,
         options: Vec<acp::PermissionOption>,
+        respect_always_allow_setting: bool,
         cx: &mut Context<Self>,
     ) -> Result<BoxFuture<'static, acp::RequestPermissionOutcome>> {
         let (tx, rx) = oneshot::channel();
 
-        if AgentSettings::get_global(cx).always_allow_tool_actions {
+        if respect_always_allow_setting && AgentSettings::get_global(cx).always_allow_tool_actions {
             // Don't use AllowAlways, because then if you were to turn off always_allow_tool_actions,
             // some tools would (incorrectly) continue to auto-accept.
             if let Some(allow_once_option) = options.iter().find_map(|option| {

crates/acp_thread/src/connection.rs

@@ -75,6 +75,15 @@ pub trait AgentConnection {
     fn telemetry(&self) -> Option<Rc<dyn AgentTelemetry>> {
         None
     }
+
+    fn session_modes(
+        &self,
+        _session_id: &acp::SessionId,
+        _cx: &App,
+    ) -> Option<Rc<dyn AgentSessionModes>> {
+        None
+    }
+
     fn into_any(self: Rc<Self>) -> Rc<dyn Any>;
 }
 
@@ -109,6 +118,14 @@ pub trait AgentTelemetry {
     ) -> Task<Result<serde_json::Value>>;
 }
 
+pub trait AgentSessionModes {
+    fn current_mode(&self) -> acp::SessionModeId;
+
+    fn all_modes(&self) -> Vec<acp::SessionMode>;
+
+    fn set_mode(&self, mode: acp::SessionModeId, cx: &mut App) -> Task<Result<()>>;
+}
+
 #[derive(Debug)]
 pub struct AuthRequired {
     pub description: Option<String>,
@@ -397,6 +414,7 @@ mod test_support {
                                     thread.request_tool_call_authorization(
                                         tool_call.clone().into(),
                                         options.clone(),
+                                        false,
                                         cx,
                                     )
                                 })??