fix: improve startup error reporting with full stderr logging and dependency pre-check

Radiosonde route now runs a quick import check before launching the full
subprocess, catching missing Python dependencies immediately with a clear
message instead of a truncated traceback. Error messages are context-aware:
import errors suggest re-running setup.sh rather than checking SDR connections.

Increased stderr truncation limit from 200 to 500 chars and added full stderr
logging via logger.error() across all affected routes (radiosonde, ais, aprs,
acars, vdl2) for easier debugging.

Closes #173

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

routes/acars.py

@@ -366,9 +366,11 @@ def start_acars() -> Response:
             stderr = ''
             if process.stderr:
                 stderr = process.stderr.read().decode('utf-8', errors='replace')
-            error_msg = f'acarsdec failed to start'
             if stderr:
-                error_msg += f': {stderr[:200]}'
+                logger.error(f"acarsdec stderr:\n{stderr}")
+            error_msg = 'acarsdec failed to start'
+            if stderr:
+                error_msg += f': {stderr[:500]}'
             logger.error(error_msg)
             return jsonify({'status': 'error', 'message': error_msg}), 500
 

routes/ais.py

@@ -450,9 +450,11 @@ def start_ais():
                     stderr_output = app_module.ais_process.stderr.read().decode('utf-8', errors='ignore').strip()
                 except Exception:
                     pass
+            if stderr_output:
+                logger.error(f"AIS-catcher stderr:\n{stderr_output}")
             error_msg = 'AIS-catcher failed to start. Check SDR device connection.'
             if stderr_output:
-                error_msg += f' Error: {stderr_output[:200]}'
+                error_msg += f' Error: {stderr_output[:500]}'
             return jsonify({'status': 'error', 'message': error_msg}), 500
 
         ais_running = True

routes/aprs.py

@@ -1870,9 +1870,11 @@ def start_aprs() -> Response:
                     stderr_output = remaining.decode('utf-8', errors='replace').strip()
             except Exception:
                 pass
+            if stderr_output:
+                logger.error(f"rtl_fm stderr:\n{stderr_output}")
             error_msg = f'rtl_fm failed to start (exit code {rtl_process.returncode})'
             if stderr_output:
-                error_msg += f': {stderr_output[:200]}'
+                error_msg += f': {stderr_output[:500]}'
             logger.error(error_msg)
             try:
                 os.close(master_fd)

routes/radiosonde.py

@@ -586,6 +586,26 @@ def start_radiosonde():
     # Set cwd to the auto_rx directory so 'from autorx.scan import ...' works
     auto_rx_dir = os.path.dirname(os.path.abspath(auto_rx_path))
 
+    # Quick dependency check before launching the full process
+    if auto_rx_path.endswith('.py'):
+        dep_check = subprocess.run(
+            [sys.executable, '-c', 'import autorx.scan'],
+            cwd=auto_rx_dir,
+            capture_output=True,
+            timeout=10,
+        )
+        if dep_check.returncode != 0:
+            dep_error = dep_check.stderr.decode('utf-8', errors='ignore').strip()
+            logger.error(f"radiosonde_auto_rx dependency check failed:\n{dep_error}")
+            app_module.release_sdr_device(device_int, sdr_type_str)
+            return jsonify({
+                'status': 'error',
+                'message': (
+                    'radiosonde_auto_rx dependencies not satisfied. '
+                    f'Re-run setup.sh to install. Error: {dep_error[:500]}'
+                ),
+            }), 500
+
     try:
         logger.info(f"Starting radiosonde_auto_rx: {' '.join(cmd)}")
         app_module.radiosonde_process = subprocess.Popen(
@@ -609,9 +629,23 @@ def start_radiosonde():
                     ).strip()
                 except Exception:
                     pass
-            error_msg = 'radiosonde_auto_rx failed to start. Check SDR device connection.'
             if stderr_output:
-                error_msg += f' Error: {stderr_output[:200]}'
+                logger.error(f"radiosonde_auto_rx stderr:\n{stderr_output}")
+            if stderr_output and (
+                'ImportError' in stderr_output
+                or 'ModuleNotFoundError' in stderr_output
+            ):
+                error_msg = (
+                    'radiosonde_auto_rx failed to start due to missing Python '
+                    'dependencies. Re-run setup.sh or reinstall radiosonde_auto_rx.'
+                )
+            else:
+                error_msg = (
+                    'radiosonde_auto_rx failed to start. '
+                    'Check SDR device connection.'
+                )
+            if stderr_output:
+                error_msg += f' Error: {stderr_output[:500]}'
             return jsonify({'status': 'error', 'message': error_msg}), 500
 
         radiosonde_running = True

routes/vdl2.py

@@ -306,9 +306,11 @@ def start_vdl2() -> Response:
             stderr = ''
             if process.stderr:
                 stderr = process.stderr.read().decode('utf-8', errors='replace')
+            if stderr:
+                logger.error(f"dumpvdl2 stderr:\n{stderr}")
             error_msg = 'dumpvdl2 failed to start'
             if stderr:
-                error_msg += f': {stderr[:200]}'
+                error_msg += f': {stderr[:500]}'
             logger.error(error_msg)
             return jsonify({'status': 'error', 'message': error_msg}), 500