Store: newest query runs after a source's current search; no source calls under the search lock

A search for a different query while a source is busy now queues (newest wins)
instead of being dropped, and warm() uses the browse limit so the first browse
reuses it. set_enabled calls the source before taking search._lock. A
SourceLimited error reports the source as 'limited'.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

ui/apk_sources/__init__.py

@@ -43,3 +43,11 @@ Rules
 
 class SourceError(Exception):
     """User-readable failure from a source (network, format, verification)."""
+
+
+class SourceLimited(SourceError):
+    """The source's host asked us to slow down; retry_after is in seconds."""
+
+    def __init__(self, message, retry_after=None):
+        super().__init__(message)
+        self.retry_after = retry_after

ui/apk_sources/search.py

@@ -15,10 +15,11 @@ import time
 import unicodedata
 
 import frame_host
-from apk_sources import SourceError
+from apk_sources import SourceError, SourceLimited
 
 _lock = threading.RLock()
 _running = {}
+_pending = {}  # source id -> newest query waiting for the running one
 _status = {}
 TIMEOUT = 12
 
@@ -84,9 +85,9 @@ def resolve(source_id):
 
 def set_enabled(source_id, enabled):
     module, source = resolve(source_id)
+    if hasattr(module, 'set_enabled'):
+        module.set_enabled(source_id, enabled)  # never call into a source while holding _lock
     with _lock:
-        if hasattr(module, 'set_enabled'):
-            module.set_enabled(source_id, enabled)
         values = overrides()
         values[source_id] = enabled
         path = settings_path()
@@ -208,23 +209,46 @@ def group(entries, query='', vr=None, installable=False):
 
 
 def _launch(module, source, query, limit):
+    """One search per source at a time; the newest different query runs next."""
     key = source['id']
+    task = {'event': threading.Event(), 'query': (query, limit), 'started': time.monotonic(),
+            'job': (module, source)}
     with _lock:
         old = _running.get(key)
         if old and not old['event'].is_set():
-            return old if old['query'] == query else None
-        task = {'event': threading.Event(), 'query': query, 'started': time.monotonic()}
+            if old['query'] == task['query']:
+                return old
+            queued = _pending.get(key)
+            if queued and queued['query'] == task['query']:
+                return queued
+            _pending[key] = task
+            return task
         _running[key] = task
+    _start(key, task)
+    return task
+
+
+def _start(key, task):
+    module, source = task['job']
+    query, limit = task['query']
+
     def run():
+        queued = None
         try:
             task['entries'] = [dict(e, source=key, source_name=source['name'], trust=source.get('trust'))
                                for e in module.search(source, query, limit=limit) if e.get('free') is True]
         except Exception as e:
             task['error'] = str(e)
+            task['limited'] = isinstance(e, SourceLimited)
         finally:
+            with _lock:
+                queued = _pending.pop(key, None)
+                if queued:
+                    _running[key] = queued
             task['event'].set()
+        if queued:
+            _start(key, queued)
     threading.Thread(target=run, daemon=True).start()
-    return task
 
 
 def search(query='', vr=None, source=None, installable=False, timeout=TIMEOUT, limit=50):
@@ -238,11 +262,11 @@ def search(query='', vr=None, source=None, installable=False, timeout=TIMEOUT, l
     entries, statuses = [], list(errors)
     for s, task in tasks:
         status = {'id': s['id'], 'name': s['name']}
-        if task is None or not task['event'].wait(max(0, task['started'] + timeout - time.monotonic())):
+        if not task['event'].wait(max(0, task['started'] + timeout - time.monotonic())):
             # Still working (e.g. first download of a large index); it keeps going and fills the cache.
             status.update(status='loading')
         elif 'error' in task:
-            status.update(status='error', error=task['error'])
+            status.update(status='limited' if task.get('limited') else 'error', error=task['error'])
         else:
             status.update(status='ok')
             entries.extend(task['entries'])
@@ -257,7 +281,7 @@ def warm():
     items, _ = registry()
     for m, s in items:
         if s['enabled'] and not s.get('page_only'):
-            _launch(m, s, '', 1)
+            _launch(m, s, '', 50)  # same as the first browse, so that search reuses it
 
 
 def install(source_id, entry_id, version_code=None, progress=None):