fix(deploy): Prevent backend re-execution on Streamlit rerun

launcher.py

@@ -1,52 +1,52 @@
-# Full Code for: launcher.py
+# Full, Final, and Corrected Code for: launcher.py
 
+import streamlit as st
 import subprocess
 import time
 import os
 
-# --- Step 1: Launch the FastAPI Backend ---
-# We use subprocess.Popen to start the backend in a new process,
-# which runs in the background. We redirect its output to a log file.
-
-print("--- LAUNCHER: Starting backend server... ---")
-
-# We construct the command to run uvicorn
-backend_command = [
-    "uvicorn",
-    "v2_multilingual_api.backend.main:app",
-    "--host", "0.0.0.0",
-    "--port", "8000"
-]
-
-# Open log files for the backend's output and errors
-backend_log = open("backend.log", "w")
-
-# Start the backend process
-backend_process = subprocess.Popen(backend_command, stdout=backend_log, stderr=backend_log)
-
-print(f"--- LAUNCHER: Backend process started with PID: {backend_process.pid} ---")
-print("--- LAUNCHER: Waiting 20 seconds for backend to initialize models... ---")
-time.sleep(20)
-
-# --- Step 2: Health Check for the Backend ---
-# Check if the process is still running. If poll() returns a number, it means it crashed.
-if backend_process.poll() is not None:
-    print("--- LAUNCHER: !!! BACKEND FAILED TO START !!! ---")
-    # Read the log file to find out why it failed
-    backend_log.close()
-    with open("backend.log", "r") as f:
-        print(f.read())
-    # Exit the launcher with an error code to make the build fail clearly
-    exit(1)
-else:
-    print("--- LAUNCHER: Backend health check passed. Process is running. ---")
-
-
+# --- Use Streamlit's session state to ensure this runs only ONCE ---
+if 'backend_process' not in st.session_state:
+    print("--- LAUNCHER: First run. Starting backend server... ---")
+    
+    # We construct the command to run uvicorn
+    backend_command = [
+        "uvicorn",
+        "v2_multilingual_api.backend.main:app",
+        "--host", "0.0.0.0",
+        "--port", "8000"
+    ]
+    
+    # Open log files for the backend's output and errors
+    backend_log = open("backend.log", "w")
+    
+    # Start the backend process and store it in the session state
+    st.session_state.backend_process = subprocess.Popen(
+        backend_command, stdout=backend_log, stderr=backend_log
+    )
+
+    print(f"--- LAUNCHER: Backend process started with PID: {st.session_state.backend_process.pid} ---")
+    print("--- LAUNCHER: Waiting 20 seconds for backend to initialize models... ---")
+    time.sleep(20)
+
+    # --- Health Check for the Backend ---
+    # Check if the process crashed during startup
+    if st.session_state.backend_process.poll() is not None:
+        print("--- LAUNCHER: !!! BACKEND FAILED TO START ON INITIALIZATION !!! ---")
+        backend_log.close()
+        with open("backend.log", "r") as f:
+            print(f.read())
+        st.error("The backend server failed to start. Please check the logs.")
+        # We use st.stop() to halt the app if the backend fails
+        st.stop()
+    else:
+        print("--- LAUNCHER: Backend health check passed. Process is running. ---")
+        
 # --- Step 3: Launch the Streamlit Frontend ---
-# This command will run in the foreground and take over the main process.
-# This is what the Hugging Face Spaces platform expects.
+# This part of the code will run every time, but the backend is already running.
+# The command is to run the *actual* frontend app file.
 
-print("--- LAUNCHER: Starting frontend server... ---")
+print("--- LAUNCHER: Handing off to the main Streamlit frontend application. ---")
 
 # We use os.system for simplicity to run the final command
 frontend_command = (
@@ -55,7 +55,4 @@ frontend_command = (
     "--server.address 0.0.0.0"
 )
 
-os.system(frontend_command)
-
-# Close the log file when the app is shut down
-backend_log.close()
+os.system(frontend_command)