fix(player): restart backward HLS seeks (#499)

Preserve negative player-time offsets for targets before a copy-mode HLS window so the existing transcode restart path handles them.

Co-authored-by: GPT-5.6 Sol <noreply@openai.com>

web/src/player/utils/mediaTimeline.test.ts

@@ -8,9 +8,9 @@ describe("toMediaTime / toPlayerTime", () => {
     expect(toPlayerTime(3060, 3000)).toBe(60);
   });
 
-  it("never returns a negative time", () => {
+  it("preserves an out-of-window target before the stream origin", () => {
     expect(toMediaTime(-10, 0)).toBe(0);
-    expect(toPlayerTime(10, 3000)).toBe(0);
+    expect(toPlayerTime(10, 3000)).toBe(-2990);
   });
 });
 

web/src/player/utils/mediaTimeline.ts

@@ -3,7 +3,9 @@ export function toMediaTime(playerTimeSeconds: number, streamOriginSeconds = 0):
 }
 
 export function toPlayerTime(mediaTimeSeconds: number, streamOriginSeconds = 0): number {
-  return Math.max(0, mediaTimeSeconds - streamOriginSeconds);
+  // Preserve negative offsets so callers can distinguish a target before the
+  // current HLS window from the locally seekable position at zero.
+  return mediaTimeSeconds - streamOriginSeconds;
 }
 
 /**