fix: SSTV VIS detector stuck in DETECTED state on validation failure

The previous fix (f29ae3d) introduced a regression: when VIS parity
check failed or the VIS code was unrecognized, the detector entered
DETECTED state permanently and never resumed scanning. Now it resets
to IDLE on validation failure and only enters DETECTED on success.

Also resets partial image progress counter between consecutive decodes
and adds SDR device claiming to general SSTV route to prevent conflicts.

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

routes/sstv_general.py

@@ -13,6 +13,7 @@ from pathlib import Path
 
 from flask import Blueprint, Response, jsonify, request, send_file
 
+import app as app_module
 from utils.logging import get_logger
 from utils.sse import format_sse
 from utils.event_pipeline import process_event
@@ -27,6 +28,9 @@ sstv_general_bp = Blueprint('sstv_general', __name__, url_prefix='/sstv-general'
 # Queue for SSE progress streaming
 _sstv_general_queue: queue.Queue = queue.Queue(maxsize=100)
 
+# Track which device is being used
+_sstv_general_active_device: int | None = None
+
 # Predefined SSTV frequencies
 SSTV_FREQUENCIES = [
     {'band': '80 m', 'frequency': 3.845, 'modulation': 'lsb', 'notes': 'Common US SSTV calling frequency', 'type': 'Terrestrial HF'},
@@ -150,6 +154,17 @@ def start_decoder():
             'message': 'Modulation must be fm, usb, or lsb',
         }), 400
 
+    # Claim SDR device
+    global _sstv_general_active_device
+    device_int = int(device_index)
+    error = app_module.claim_sdr_device(device_int, 'sstv_general')
+    if error:
+        return jsonify({
+            'status': 'error',
+            'error_type': 'DEVICE_BUSY',
+            'message': error,
+        }), 409
+
     # Set callback and start
     decoder.set_callback(_progress_callback)
     success = decoder.start(
@@ -159,6 +174,7 @@ def start_decoder():
     )
 
     if success:
+        _sstv_general_active_device = device_int
         return jsonify({
             'status': 'started',
             'frequency': frequency,
@@ -166,6 +182,7 @@ def start_decoder():
             'device': device_index,
         })
     else:
+        app_module.release_sdr_device(device_int)
         return jsonify({
             'status': 'error',
             'message': 'Failed to start decoder',
@@ -175,8 +192,14 @@ def start_decoder():
 @sstv_general_bp.route('/stop', methods=['POST'])
 def stop_decoder():
     """Stop general SSTV decoder."""
+    global _sstv_general_active_device
     decoder = get_general_sstv_decoder()
     decoder.stop()
+
+    if _sstv_general_active_device is not None:
+        app_module.release_sdr_device(_sstv_general_active_device)
+        _sstv_general_active_device = None
+
     return jsonify({'status': 'stopped'})
 
 

utils/sstv/sstv_decoder.py

@@ -475,6 +475,7 @@ class SSTVDecoder:
                         mode_spec = get_mode(vis_code)
                         if mode_spec:
                             current_mode_name = mode_name
+                            last_partial_pct = -1
                             image_decoder = SSTVImageDecoder(
                                 mode_spec,
                                 sample_rate=SAMPLE_RATE,

utils/sstv/vis.py

@@ -298,16 +298,26 @@ class VISDetector:
 
             if self._tone_counter >= self._bit_windows:
                 result = self._validate_and_decode()
-                # Do NOT call reset() here. self._buffer still holds samples
-                # that arrived after the STOP_BIT window — those are the very
-                # first samples of the image. Wiping the buffer here causes all
-                # of them to be lost, making the image decoder start mid-stream
-                # and producing garbled/diagonal output.
-                # feed() will advance past the current window, leaving
-                # self._buffer pointing at the image start. The caller must
-                # read remaining_buffer and then call reset() explicitly.
-                self._state = VISState.DETECTED
-                return result
+                if result is not None:
+                    # Do NOT call reset() here. self._buffer still holds
+                    # samples that arrived after the STOP_BIT window — those
+                    # are the very first samples of the image. Wiping the
+                    # buffer here causes all of them to be lost, making the
+                    # image decoder start mid-stream and producing
+                    # garbled/diagonal output.
+                    # feed() will advance past the current window, leaving
+                    # self._buffer pointing at the image start. The caller
+                    # must read remaining_buffer and then call reset().
+                    self._state = VISState.DETECTED
+                    return result
+                else:
+                    # Parity failure or unknown VIS code — reset and
+                    # continue scanning for the next VIS header.
+                    self._tone_counter = 0
+                    self._data_bits = []
+                    self._parity_bit = 0
+                    self._bit_accumulator = []
+                    self._state = VISState.IDLE
 
         elif self._state == VISState.DETECTED:
             # Waiting for caller to call reset() after reading remaining_buffer.