engine-v0.5.0

Added

• Model downloads are configurable as one ModelAssetSources value: the persistent file cache, the request strategy, and the URLs of the ONNX WebAssembly runtime. DirectModelFileFetcher names transport failures, while RelayFallbackModelFileFetcher retries an unreachable host through a relay without changing the cache key and remembers that host for the rest of the run. WhisperTranscriber now takes this value as its third constructor argument instead of a bare ModelFileCache.
• CSS resource embedding has an explicit outbound-request policy. BrowserCssResourceEmbedder now requires a CssResourceUrlPolicy; AnyOriginCssResourceUrlPolicy preserves the browser-rendering behaviour, and SameMachineCssResourceUrlPolicy limits a hosted renderer to blob: and same-origin URLs. The default RenderPipelineBuilder remains permissive.
• IsolatedWordLineSplitter puts one word of each segment alone on the second line, so a stylesheet can size it as that line. The word is the latest one with at least minLetters letters that stays on screen for minSecondsOnScreen, counted from when it is said until the next segment starts or holdAfterLastWordSeconds after the last word, whichever comes first. Words after it take a third line; when no word qualifies, the segment stays on one line.
• --previous-line-width-em on every line after the first: the measured width of the line above, in the same unit as --line-width-em, so a stylesheet can align two lines against each other.
• FixedTailLineSplitterConfig.minWordsToSplit, the fewest words a segment needs before it is split. Defaults to 3, the value the splitter always used.
• VideoEncoderSelectionFailedError identifies a render that cannot start because the browser supports none of the codecs accepted by the output format. Its stable name and ERROR_NAME survive worker and browser-automation boundaries.

Changed

• An export decodes only the video it keeps. A cut of three seconds or more is seeked past rather than decoded and thrown away frame by frame, so decode cost follows the output's length instead of the source's. On a 60 s source with 54 s cut, 1439 decoded frames become 145: 3387 ms to 636 ms at 4K, and 1565 ms to 219 ms at 1080p. Shorter cuts are still read through, because a seek resumes at the key frame before it and measured h264 sources key every 1.0 s to 3.5 s. VideoFrameDecoder gains canSeek() and an optional span on samples(); a decoder answering false still receives the whole track.
• SubtitleStyle.wordOverrides is now subtreeOverrides. The broader name reflects that overrides can target lines and decorations as well as words. This is a breaking rename for consumers that construct subtitle styles.

Fixed

• A line written entirely against the declared direction is laid out on its own base. RenderingConfig.textDirection states the language of the captions, so a caption holding one whole English sentence inside a right-to-left document painted as [.] [This] [is] [a] [test]: the full stop is neutral, its right-hand neighbour is the paragraph boundary, and UAX #9 resolves that tie toward the paragraph direction. LineBaseDirectionResolver overrides the base for a line carrying strong characters of one direction only, where the base moves the neutrals at the edges and can reorder nothing. A line mixing both keeps the declared base. WordFragmenter takes the resolver as its third constructor argument.
• A fragment of a word that paints away from the rest of it no longer carries the word's decorations. A word split across embedding levels is emitted as one element per piece, and a stylesheet drawing a background on .word-being-narrated painted it twice, at opposite ends of a mixed line: a right-to-left line closing on this is a test. paints as [.] [this] [is] [a] [test], with the right-to-left words further right, so the pill landed on test and again on the full stop with three words between them. WordFragment.carriesWordBody is false on such a piece and the renderers add the detached-word-fragment class, which a rule that points at a word excludes. Pieces that paint flush against each other are all body, so a word whose punctuation lands beside it still highlights as one box. The state class and the timing variables stay on every piece: a stray is read at the same moment as the rest of its word. WordFragmenter takes a BidiCharacterClassifier as its fourth constructor argument.
• Segment and line inline styles land on the element they describe instead of being merged into an outer wrapper. Template rules can no longer override a chosen element font merely because the font was inherited, and line-level overrides now reach exported frames.