android: a streamed file copied into a folder, the listening port, the dev build's diagnostics

The now-playing sheet's streamed track can be copied into a folder picked
on the phone, as the file it is — the cache written out, nothing downloaded
again, no library row (copy_stream_to_folder, which the desktop has had a
command for and no UI). You → Sharing carries the listening port, what
peers dial when they download from you: unset is the client's own 50300,
the app asks the router to forward it over UPnP and falls back to the
server relaying, and a change applies on the next connect. The dev flavour
gets the desktop's debug overlay as a screen under This phone — CPU,
memory, the network, the stream and its loudness, what the pre-buffer is
fetching, the size of the play history — behind devBuild in util.js, which
is Vite's own DEV flag, so the embedded build the phone keeps has no row
to tap.

ANDROID.md

@@ -237,7 +237,11 @@ Library clears the play history behind a confirm. The now-playing
 sheet's ⋯ on a streamed track is the desktop's
 Save menu: Save to library (at once when the cache is byte-complete, else
 through the download pipeline) and Save this record for the streamed
-record the queue holds. A moment after boot the phone warms the library's thumbnails the
+record the queue holds; beside them, "Copy to a folder…" writes that same
+cached stream into a folder picked on this phone, as the plain file it is
+(`copy_stream_to_folder` — no re-download, no tagging, no library row; a
+track that has not finished streaming is counted back, never fetched).
+A moment after boot the phone warms the library's thumbnails the
 desktop's way (`library_art_prewarm` at the cards' edge, one decode at a
 time behind the tiles' gate). The network results carry the hub's filters (a free slot only; FLAC or
 MP3 320+), and the lyrics sheet has the desktop's paste door (plain text,
@@ -422,6 +426,29 @@ the lyric alignment models (a desktop runtime), artist artwork's upscaler.
 Search's empty page lists the recent searches this phone used (the last
 eight: Enter, or the screen left with a query in it), kept on the device.
 
+Sharing carries one thing the desktop never exposed at all: the listening
+port (`listenPort`), what other peers dial when they download from you.
+Unset means the client's own 50300 (`DEFAULT_LISTEN_PORT`; bind walks
+forward a few ports if it is taken); the app asks the router to forward it
+over UPnP and falls back to the server relaying the connection, and a
+change applies on the next connect — on mobile data the carrier's NAT
+blocks incoming connections whatever the number is. `set_settings` only
+assigns a port that is Some, so it can be changed but never taken back to
+unset: the phone walk saves a spare number and then 50300, which is the
+port an unset config already used.
+
+The dev flavour gets one more row under This phone: Diagnostics
+(`screens/Diagnostics.svelte`), the desktop's Ctrl+Shift+D overlay as a
+screen — process and system CPU, memory, the network rates, the track
+playing with its loudness correction, the tracks the pre-buffer is
+fetching, and how big the play history has grown (`debug_stats`,
+`play_row_count`), polled once a second while it is open and never
+otherwise. `devBuild` in `util.js` is the gate: Vite's own DEV flag, true
+only for the build that loads from the dev server over the cable, so the
+embedded build the phone keeps has no row to tap. The GPU counters are
+Windows PDH and the private commit is a Win32 call, so neither is on the
+screen — off Windows they report None and 0.
+
 ## Background playback and the lock-screen card
 
 The service is started with `startForegroundService`, so it promotes itself