feat(unstable): add cwd and mcp_servers to session/fork (#333)

* feat(unstable): add cwd and mcp_servers to session/fork

See #326.

I did not run generate yet, as it changes a bunch of unrelated lines for me.

* Generate schema

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

Author: SteffenDE

docs/protocol/draft/schema.mdx

@@ -235,6 +235,12 @@ these keys.
 
 See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)
 
+</ResponseField>
+<ResponseField name="cwd" type={"string"} required>
+  The working directory for this session.
+</ResponseField>
+<ResponseField name="mcpServers" type={<><span><a href="#mcpserver">McpServer</a></span><span>[]</span></>} >
+  List of MCP servers to connect to for this session.
 </ResponseField>
 <ResponseField name="sessionId" type={<a href="#sessionid">SessionId</a>} required>
   The ID of the session to fork.

schema/schema.unstable.json

@@ -1134,6 +1134,17 @@
           "description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
           "type": ["object", "null"]
         },
+        "cwd": {
+          "description": "The working directory for this session.",
+          "type": "string"
+        },
+        "mcpServers": {
+          "description": "List of MCP servers to connect to for this session.",
+          "items": {
+            "$ref": "#/$defs/McpServer"
+          },
+          "type": "array"
+        },
         "sessionId": {
           "allOf": [
             {
@@ -1143,7 +1154,7 @@
           "description": "The ID of the session to fork."
         }
       },
-      "required": ["sessionId"],
+      "required": ["sessionId", "cwd"],
       "type": "object",
       "x-method": "session/fork",
       "x-side": "agent"

src/agent.rs

@@ -621,6 +621,11 @@ impl LoadSessionResponse {
 pub struct ForkSessionRequest {
     /// The ID of the session to fork.
     pub session_id: SessionId,
+    /// The working directory for this session.
+    pub cwd: PathBuf,
+    /// List of MCP servers to connect to for this session.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub mcp_servers: Vec<McpServer>,
     /// The _meta property is reserved by ACP to allow clients and agents to attach additional
     /// metadata to their interactions. Implementations MUST NOT make assumptions about values at
     /// these keys.
@@ -632,13 +637,22 @@ pub struct ForkSessionRequest {
 
 #[cfg(feature = "unstable_session_fork")]
 impl ForkSessionRequest {
-    pub fn new(session_id: impl Into<SessionId>) -> Self {
+    pub fn new(session_id: impl Into<SessionId>, cwd: impl Into<PathBuf>) -> Self {
         Self {
             session_id: session_id.into(),
+            cwd: cwd.into(),
+            mcp_servers: vec![],
             meta: None,
         }
     }
 
+    /// List of MCP servers to connect to for this session.
+    #[must_use]
+    pub fn mcp_servers(mut self, mcp_servers: Vec<McpServer>) -> Self {
+        self.mcp_servers = mcp_servers;
+        self
+    }
+
     /// The _meta property is reserved by ACP to allow clients and agents to attach additional
     /// metadata to their interactions. Implementations MUST NOT make assumptions about values at
     /// these keys.

src/bin/generate.rs

@@ -759,11 +759,8 @@ starting with '$/' it is free to ignore the notification."
                             other_type = Some(t);
                         }
                     }
-                    if has_null && other_type.is_some() {
-                        return format!(
-                            "<><span>{}</span><span> | null</span></>",
-                            other_type.unwrap()
-                        );
+                    if has_null && let Some(other_type) = other_type {
+                        return format!("<><span>{other_type}</span><span> | null</span></>");
                     }
                 }
                 return "union".to_string();