refactor(vscode-ide-companion): migrate session save to CLI /chat save command

- Replace manual checkpoint file writing with CLI's native /chat save command
- Add saveCheckpointViaCommand method to use CLI's built-in save functionality
- Deprecate saveSessionViaAcp as CLI doesn't support session/save ACP method
- Update saveCheckpoint to delegate to CLI command for complete context preservation
- Enhanced error logging in acpSessionManager session load
- Mark saveSessionViaAcp as deprecated with fallback to command-based save
- Fix ESLint errors: remove unused imports and catch variables, wrap case block declarations

This ensures checkpoints are saved with complete session context including tool calls,
leveraging CLI's native save functionality instead of manual file operations.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/vscode-ide-companion/src/acp/acpSessionManager.ts

@@ -248,20 +248,46 @@ export class AcpSessionManager {
     pendingRequests: Map<number, PendingRequest<unknown>>,
     nextRequestId: { value: number },
   ): Promise<AcpResponse> {
-    console.log('[ACP] Loading session:', sessionId);
-    const response = await this.sendRequest<AcpResponse>(
-      AGENT_METHODS.session_load,
-      {
-        sessionId,
-        cwd: process.cwd(),
-        mcpServers: [],
-      },
-      child,
-      pendingRequests,
-      nextRequestId,
-    );
-    console.log('[ACP] Session load response:', response);
-    return response;
+    console.log('[ACP] Sending session/load request for session:', sessionId);
+    console.log('[ACP] Request parameters:', {
+      sessionId,
+      cwd: process.cwd(),
+      mcpServers: [],
+    });
+
+    try {
+      const response = await this.sendRequest<AcpResponse>(
+        AGENT_METHODS.session_load,
+        {
+          sessionId,
+          cwd: process.cwd(),
+          mcpServers: [],
+        },
+        child,
+        pendingRequests,
+        nextRequestId,
+      );
+
+      console.log(
+        '[ACP] Session load response:',
+        JSON.stringify(response).substring(0, 500),
+      );
+
+      // Check if response contains an error
+      if (response.error) {
+        console.error('[ACP] Session load returned error:', response.error);
+      } else {
+        console.log('[ACP] Session load succeeded');
+      }
+
+      return response;
+    } catch (error) {
+      console.error(
+        '[ACP] Session load request failed with exception:',
+        error instanceof Error ? error.message : String(error),
+      );
+      throw error;
+    }
   }
 
   /**