fix: skip disposable pictures during local seek preroll

Checks/local-seek.mm

@@ -0,0 +1,68 @@
+// Exercise the real local seek/decode/presentation loop without worker races.
+#include "../Sources/Core/player.cpp"
+#include <cstdio>
+#include <cstdlib>
+
+static void require(bool condition, const char *message) {
+    if (!condition) { std::fprintf(stderr, "FAIL: %s\n", message); std::exit(1); }
+}
+static std::vector<uint8_t> pixels(const AVFrame *frame) {
+    const auto format = static_cast<AVPixelFormat>(frame->format);
+    const int size = av_image_get_buffer_size(format, frame->width, frame->height, 1);
+    require(size > 0, "preview has readable pixels");
+    std::vector<uint8_t> bytes(size);
+    require(av_image_copy_to_buffer(bytes.data(), size, frame->data, frame->linesize,
+        format, frame->width, frame->height, 1) == size, "copy preview pixels");
+    return bytes;
+}
+
+
+int main(int argc, char **argv) {
+    require(argc > 1, "provide local media fixtures");
+    for (int i = 1; i < argc; ++i) {
+        av_log_set_level(AV_LOG_ERROR);
+        Player player;
+        player.shutdown();
+        player.stopping.store(false);
+        player.activeEpoch = player.requestedEpoch.load();
+        player.open(Command{Action::Open, argv[i]});
+        require(player.tracks[1].codec && player.canSeek, "seekable local video");
+        player.output.set_volume(0);
+        for (bool playing : {false, true}) {
+            for (double fraction : {.01, .79, .21, .59}) {
+                const double target = player.duration * fraction;
+                // Full reference decoding supplies an independent expected picture,
+                // including disposable B-frames at or immediately after the target.
+                player.seek(target, false);
+                VideoFrame expected{};
+                const auto referenceStart = Clock::now();
+                while (!expected.frame && Clock::now() - referenceStart < std::chrono::seconds(5)) {
+                    player.decodeOne(true);
+                    while (!player.video.empty()) {
+                        auto frame = std::move(player.video.front());
+                        player.videoBytes -= frame.bytes;
+                        player.video.pop_front();
+                        if (frame.pts + sampleTime * .5 >= target) {
+                            expected = std::move(frame);
+                            break;
+                        }
+                    }
+                }
+                require(bool(expected.frame), "full decode supplies reference picture");
+                const auto start = Clock::now();
+                player.seek(target, playing);
+                while ((!player.presented.frame || player.presented.pts < target - .002) &&
+                       Clock::now() - start < std::chrono::seconds(5))
+                    player.tick();
+                const double elapsed = std::chrono::duration<double, std::milli>(Clock::now() - start).count();
+                std::printf("local-seek fixture=%s playing=%d target=%.3f preview=%.3f latency_ms=%.3f\n",
+                    argv[i], playing, target, player.presented.pts, elapsed);
+                require(player.presented.frame && player.presented.pts == expected.pts &&
+                        pixels(player.presented.frame.get()) == pixels(expected.frame.get()),
+                        "seek presents the exact fully decoded picture, including B-frame targets");
+                require(player.status == (playing ? PLAYER_PLAYING : PLAYER_PAUSED),
+                        "seek preserves playback intent");
+            }
+        }
+    }
+}