fix(player): survive a flaky stream, and don't read 0:00 at EOF

Two MPV-side fixes for the same failure story — a wifi blip during
playback.

The demuxer gave up the moment a read failed and MPV raised
EndFile(ERROR), so a momentary outage killed the track outright. Enabling
ffmpeg's reconnect options handles the common case entirely below our
level, so most outages never reach the recovery path at all. Set
non-fatally: their availability varies with the libmpv/ffmpeg build, and
losing resilience is not a reason to refuse to play anything.

Separately, `time-pos` and `duration` are live properties of the *loaded*
file: at EOF MPV unloads it and both stop resolving. Reading them straight
through returned 0.0/unknown at exactly the moment end-of-file handling
needed to know where playback had reached, so the player appeared to
rewind to 0:00 as a track ended. `ObservedTime` records the last reading
seen while media was loaded and the accessors fall back to it.

src-tauri/src/player/stream_end.rs

@@ -102,6 +102,54 @@ pub fn with_start_time(url: &str, position_seconds: f64) -> String {
     format!("{}?{}", base, parts.join("&"))
 }
 
+/// The last playback time actually observed while media was loaded.
+///
+/// Some backends expose position and duration as **live** properties of the
+/// loaded file — MPV's `time-pos` and `duration` stop resolving the moment it
+/// unloads the file at EOF. Reading them straight through means that at exactly
+/// the moment end-of-file handling wants to know where playback got to, the
+/// answer is `0.0` / unknown: the player appears to rewind to 0:00 as it ends.
+///
+/// The polling thread records here, and the accessors fall back to it, so an EOF
+/// reads as the last timestamp rather than as zero.
+#[derive(Debug, Default, Clone, Copy)]
+pub struct ObservedTime {
+    position: f64,
+    duration: Option<f64>,
+}
+
+impl ObservedTime {
+    /// Record a live reading. Non-positive durations are treated as unknown —
+    /// that is how a backend reports "not established yet", not a real zero.
+    pub fn record(&mut self, position: f64, duration: f64) {
+        self.position = position.max(0.0);
+        if duration > 0.0 {
+            self.duration = Some(duration);
+        }
+    }
+
+    /// Record a position alone, e.g. straight after a seek, before the next poll.
+    pub fn record_position(&mut self, position: f64) {
+        self.position = position.max(0.0);
+    }
+
+    /// Forget everything — a different file is loading, and the previous one's
+    /// timestamp must not leak into it.
+    pub fn reset(&mut self) {
+        *self = Self::default();
+    }
+
+    /// The live reading if there is one, else the last observed value.
+    pub fn position_or_last(&self, live: Option<f64>) -> f64 {
+        live.filter(|p| *p >= 0.0).unwrap_or(self.position)
+    }
+
+    /// The live reading if there is one, else the last observed value.
+    pub fn duration_or_last(&self, live: Option<f64>) -> Option<f64> {
+        live.filter(|d| *d > 0.0).or(self.duration)
+    }
+}
+
 /// Budget for consecutive resume attempts that make no progress.
 ///
 /// Held by the player controller across ends of the *same* stream. Any position
@@ -225,6 +273,64 @@ mod tests {
         );
     }
 
+    /// The bug: MPV unloads the file at EOF, so `time-pos` stops resolving and a
+    /// straight read reports 0.0 — the position collapses to zero at precisely
+    /// the moment end-of-file handling needs to know where playback reached.
+    #[test]
+    fn test_eof_reads_as_the_last_observed_timestamp() {
+        let mut observed = ObservedTime::default();
+        observed.record(178.0, 180.0);
+
+        // The file is gone: both live properties fail.
+        assert_eq!(observed.position_or_last(None), 178.0);
+        assert_eq!(observed.duration_or_last(None), Some(180.0));
+    }
+
+    #[test]
+    fn test_live_readings_win_while_the_file_is_loaded() {
+        let mut observed = ObservedTime::default();
+        observed.record(178.0, 180.0);
+
+        assert_eq!(observed.position_or_last(Some(12.0)), 12.0);
+        assert_eq!(observed.duration_or_last(Some(240.0)), Some(240.0));
+    }
+
+    #[test]
+    fn test_unestablished_duration_is_not_recorded_as_zero() {
+        let mut observed = ObservedTime::default();
+        // A backend reports 0.0 for "duration not known yet", not a real zero.
+        observed.record(5.0, 0.0);
+        assert_eq!(observed.duration_or_last(None), None);
+        assert_eq!(observed.position_or_last(None), 5.0);
+
+        observed.record(6.0, 180.0);
+        assert_eq!(observed.duration_or_last(Some(0.0)), Some(180.0));
+    }
+
+    #[test]
+    fn test_reset_stops_the_previous_file_leaking_into_the_next() {
+        let mut observed = ObservedTime::default();
+        observed.record(178.0, 180.0);
+        observed.reset();
+
+        assert_eq!(observed.position_or_last(None), 0.0);
+        assert_eq!(observed.duration_or_last(None), None);
+    }
+
+    #[test]
+    fn test_seek_updates_the_last_position_before_the_next_poll() {
+        let mut observed = ObservedTime::default();
+        observed.record(10.0, 180.0);
+        observed.record_position(120.0);
+
+        assert_eq!(observed.position_or_last(None), 120.0);
+        assert_eq!(
+            observed.duration_or_last(None),
+            Some(180.0),
+            "seeking does not change how long the file is"
+        );
+    }
+
     #[test]
     fn test_resume_tracker_bounds_stalled_retries() {
         let mut tracker = ResumeTracker::default();