From 295be10658c7d46dbc0bfafe047f116adeb233be Mon Sep 17 00:00:00 2001
From: Steffen Deusch <steffen@deusch.me>
Date: Tue, 9 Dec 2025 12:16:45 +0100
Subject: [PATCH] add unstable forkSession support

---
 src/acp.ts | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/src/acp.ts b/src/acp.ts
index 7abacb9..a9ff39e 100644
--- a/src/acp.ts
+++ b/src/acp.ts
@@ -64,6 +64,13 @@ export class AgentSideConnection {
           const validatedParams = validate.zLoadSessionRequest.parse(params);
           return agent.loadSession(validatedParams);
         }
+        case schema.AGENT_METHODS.session_fork: {
+          if (!agent.forkSession) {
+            throw RequestError.methodNotFound(method);
+          }
+          const validatedParams = validate.zForkSessionRequest.parse(params);
+          return agent.forkSession(validatedParams);
+        }
         case schema.AGENT_METHODS.session_set_mode: {
           if (!agent.setSessionMode) {
             throw RequestError.methodNotFound(method);
@@ -603,6 +610,27 @@ export class ClientSideConnection implements Agent {
     );
   }
 
+  /**
+   * **UNSTABLE**
+   *
+   * This capability is not part of the spec yet, and may be removed or changed at any point.
+   *
+   * Forks an existing session to create a new independent session.
+   *
+   * Creates a new session based on the context of an existing one, allowing
+   * operations like generating summaries without affecting the original session's history.
+   *
+   * This method is only available if the agent advertises the `session.fork` capability.
+   */
+  async forkSession(
+    params: schema.ForkSessionRequest,
+  ): Promise<schema.ForkSessionResponse> {
+    return await this.#connection.sendRequest(
+      schema.AGENT_METHODS.session_fork,
+      params,
+    );
+  }
+
   /**
    * Sets the operational mode for a session.
    *
@@ -1373,6 +1401,21 @@ export interface Agent {
   loadSession?(
     params: schema.LoadSessionRequest,
   ): Promise<schema.LoadSessionResponse>;
+  /**
+   * **UNSTABLE**
+   *
+   * This capability is not part of the spec yet, and may be removed or changed at any point.
+   *
+   * Forks an existing session to create a new independent session.
+   *
+   * Creates a new session based on the context of an existing one, allowing
+   * operations like generating summaries without affecting the original session's history.
+   *
+   * This method is only available if the agent advertises the `session.fork` capability.
+   */
+  forkSession?(
+    params: schema.ForkSessionRequest,
+  ): Promise<schema.ForkSessionResponse>;
   /**
    * Sets the operational mode for a session.
    *