Fix auto_scroll end-following past code blocks / nested scrollables#6642
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Two issues broke auto_scroll's end-following when a tall child (e.g. a Markdown code block) was inserted: - The ScrollMetricsNotification listener reacted to *nested* scrollables (a code block renders inside a horizontal scroller), tracking the wrong extent. Only react to this scrollable's own metrics (notification.depth == 0). - _onScroll unpinned purely on proximity (pixels >= max - threshold). A tall insert jumps maxScrollExtent past the threshold in one frame while pixels stays put, flipping to unpinned so it stopped following. Now it only unpins when the user scrolls *up* (pixels decrease) and re-pins at the end; content growing beneath a stationary position keeps it pinned.
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The Pyodide↔Dart postMessage transport frames every packet as [type:u8][payload]
(0x00 = MsgPack Flet protocol frame, 0x01 = raw DataChannel frame), and
PyodideConnection.send_message prepends the 0x00 byte. The python_output shim,
however, posted the raw msgpack [7, {...}] with no type byte, so the Dart side
read msgpack's leading 0x92 (array-of-2 marker) as an unknown packet type and
silently dropped every stdout/stderr line — the host page's Console pane never
saw embedded-app output. Prepend the 0x00 type byte in both worker templates
(client + cookiecutter build template).
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Follow-up to the
auto_scrollend-following behavior: it stopped following once a tall child was inserted — most visibly a Markdown code block (streamed text scrolled fine, code blocks did not).Two root causes in
ScrollableControl:Nested scrollables. A Markdown code block renders inside its own horizontally-scrollable widget. The
ScrollMetricsNotificationlistener reacted to those nested notifications too, tracking the wrong (horizontal) extent. Now it ignores nested scrollables (notification.depth != 0), per the standard Flutter guidance.Extent-jump unpin.
_onScrollrecomputed the pinned state purely from proximity (pixels >= maxScrollExtent - threshold). Inserting a tall child jumpsmaxScrollExtentpast that threshold in a single frame whilepixelsstays put, so it flipped to unpinned and stopped following. Streamed text grows in sub-threshold steps so it never tripped. Now it only unpins when the user scrolls up (pixelsdecrease) and re-pins when the position returns to the end; content growing beneath a stationary position keeps it pinned.flutter analyzeon the changed control: no issues.Companion to #6637 (the original follow-content-growth change).
Summary by Sourcery
Ensure scrollable auto-follow behavior remains pinned to the end when content grows, while ignoring nested scrollable metrics.
Bug Fixes: