media3 reports STUCK_PLAYING_NOT_ENDING when the player sits in STATE_READY
past the declared duration with no renderer ending. On a tunneled MTK decoder
the clock ran a full minute past the last frame behind a black screen, so the
item never completed: no Play Next, no auto-play, and a "playing" timeline the
server kept extrapolating past the item duration.
Treat that report as the end of the file when the rendered-frame counter has
stopped as well, which separates a finished file from a container that
under-declares its duration and is still painting. The terminal event is shaped
like the STATE_ENDED one and pins the timeline at the duration first, so the
completion flow cannot mistake it for a stream that died mid-file. Shorten the
detection window to media3's stuck-playing default, and clamp a backend
hand-off to just inside the media so a fallback can no longer resume MPV past
the last frame and park there without reporting it.
close#1673
Collapse duplicated setup across the suite into six shared helpers under
test/test_helpers/ and rewrite the 28 suites that were open-coding it:
http_fixtures.dart jsonResponse() for http.Response JSON stubs
library_tab_scaffold.dart pumps library tabs under their required ancestors
multi_server_fixtures.dart MultiServerProvider wiring for widget tests
playback_report_fakes.dart PlaybackReportCall + fake report sinks
profile_stack.dart production-shaped profile dependency graph
theme.dart testMonoTokens for fast-settling widget tests
Net -1245 lines with no change in coverage or assertions.
edde746