fix: resolve rebase conflicts with upstream session_state_changed and stopReason

The SDK now includes session_state_changed in its type union, so add it
as a proper case arm instead of handling it in default. Replace the
imported StopReason type with an inline union since it's only used for
the local stopReason variable. Remove dead stopReason assignments in
error_during_execution and error_max_* cases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timvisher-dd

src/acp-agent.ts

@@ -40,7 +40,6 @@ import {
   TerminalOutputResponse,
   WriteTextFileRequest,
   WriteTextFileResponse,
-  StopReason,
 } from "@agentclientprotocol/sdk";
 import {
   CanUseTool,
@@ -511,7 +510,7 @@ export class ClaudeAcpAgent implements Agent {
 
     session.promptRunning = true;
     let handedOff = false;
-    let stopReason: StopReason = "end_turn";
+    let stopReason: "end_turn" | "max_tokens" | "cancelled" = "end_turn";
     // Saved prompt response when consuming internal turns from background
     // task completions. See the "success" result handler below.
     let savedPromptResponse: PromptResponse | undefined;
@@ -647,6 +646,12 @@ export class ClaudeAcpAgent implements Agent {
               }
               case "task_progress":
                 break;
+              case "session_state_changed": {
+                if (message.state === "idle") {
+                  return { stopReason, usage: sessionUsage(session) };
+                }
+                break;
+              }
               default:
                 unreachable(message, this.logger);
                 break;
@@ -869,7 +874,6 @@ export class ClaudeAcpAgent implements Agent {
                     message.errors.join(", ") || message.subtype,
                   );
                 }
-                stopReason = "end_turn";
                 break;
               }
               case "error_max_budget_usd":
@@ -881,7 +885,6 @@ export class ClaudeAcpAgent implements Agent {
                     message.errors.join(", ") || message.subtype,
                   );
                 }
-                stopReason = "max_turn_requests";
                 break;
               default:
                 unreachable(message, this.logger);