Fix Claude SDK spawn errors and handle expired sessions (#70)

Two issues fixed:

1. MCP Warmup "spawn node ENOENT" error
   - warmupMcpCache() was missing pathToClaudeCodeExecutable option
   - SDK fell back to spawning via 'node' which isn't in PATH when
     launched from GUI
   - Now uses getBundledClaudeBinaryPath() like the chat function

2. Session expired crash handling
   - When resuming a session that no longer exists in Claude CLI storage,
     the process would crash with "No conversation found with session ID"
   - Now detects this error, clears the invalid sessionId from database,
     and shows user-friendly "Session expired" message
   - User can simply send their message again to start fresh

Author: CorentinLumineau

src/main/lib/trpc/routers/claude.ts

@@ -300,6 +300,8 @@ export async function warmupMcpCache(): Promise<void> {
             env: buildClaudeEnv(),
             permissionMode: "bypassPermissions" as const,
             allowDangerouslySkipPermissions: true,
+            // Use bundled binary to avoid "spawn node ENOENT" errors
+            pathToClaudeCodeExecutable: getBundledClaudeBinaryPath(),
           }
         })
 
@@ -1465,7 +1467,20 @@ ${prompt}
               let errorContext = "Claude streaming error"
               let errorCategory = "UNKNOWN"
 
-              if (err.message?.includes("exited with code")) {
+              // Check for session-not-found error in stderr
+              const isSessionNotFound = stderrOutput?.includes("No conversation found with session ID")
+
+              if (isSessionNotFound) {
+                // Clear the invalid session ID from database so next attempt starts fresh
+                console.log(`[claude] Session not found - clearing invalid sessionId from database`)
+                db.update(subChats)
+                  .set({ sessionId: null })
+                  .where(eq(subChats.id, input.subChatId))
+                  .run()
+
+                errorContext = "Previous session expired. Please try again."
+                errorCategory = "SESSION_EXPIRED"
+              } else if (err.message?.includes("exited with code")) {
                 errorContext = "Claude Code process crashed"
                 errorCategory = "PROCESS_CRASH"
               } else if (err.message?.includes("ENOENT")) {

src/renderer/features/agents/lib/ipc-chat-transport.ts

@@ -82,6 +82,11 @@ const ERROR_TOAST_CONFIG: Record<
     description:
       "The Claude process exited unexpectedly. Try sending your message again or rollback.",
   },
+  SESSION_EXPIRED: {
+    title: "Session expired",
+    description:
+      "Your previous chat session expired. Send your message again to start fresh.",
+  },
   EXECUTABLE_NOT_FOUND: {
     title: "Claude CLI not found",
     description: