Clear the stranded tmpfs cache at startup

The session map is memory-only, so session directories surviving a restart
can never be served and never be evicted -- and the work root is a tmpfs,
so that is leaked RAM until reboot. The restart that ships the TTFB fix
would have stranded 1.56 GB.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

proxy/ytstream_proxy.py

@@ -735,6 +735,27 @@ def make_handler(mgr, wait_timeout, first_byte_grace=FIRST_BYTE_GRACE):
 
 # --------------------------------------------------------------------------
 
+def reset_work_root(path):
+    """Clear leftover session directories at startup. Returns bytes reclaimed.
+
+    The session map is in memory only, so anything already in the work root is
+    unreachable after a restart: it can never be served (no session to find) and
+    never be evicted (the cache accounting only sums tracked sessions). Since the
+    work root is a tmpfs, leaving it there leaks RAM until the next reboot -- a
+    restart with 1.56 GB cached stranded exactly that much.
+    """
+    reclaimed = 0
+    for name in os.listdir(path) if os.path.isdir(path) else []:
+        stale = os.path.join(path, name)
+        if not os.path.isdir(stale):
+            continue
+        out = os.path.join(stale, "out.mp4")
+        if os.path.exists(out):
+            reclaimed += os.path.getsize(out)
+        shutil.rmtree(stale, ignore_errors=True)
+    return reclaimed
+
+
 def main():
     ap = argparse.ArgumentParser(
         description="just-in-time YouTube streaming proxy for Jellyfin")
@@ -783,6 +804,11 @@ def main():
     _access_log = args.access_log
 
     os.makedirs(args.work, exist_ok=True)
+    stranded = reset_work_root(args.work)
+    if stranded:
+        log(f"cleared {stranded / 2**30:.2f} GB of untracked cache from "
+            f"{args.work} left by a previous run")
+
     mgr = Manager(args.work, args.max_pipelines,
                   int(args.cache_gb * 2**30), args.no_fetch, args.growing,
                   args.max_retries, args.max_starts, args.starts_window)