Unify handling of widget state/buffers/bufferPaths

[mscolnick]

This keeps the state/buffer/bufferPaths in sync when sending to/from the backend for the widget. This changes some typings and adds a few more tests. This is an improvement, but not the final state as we can hopefully simplify further. This does fix a few errors when sending back binary data.

Prior work done by @manzt in 9426b13

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Project	Deployment	Preview	Comments	Updated (UTC)
marimo-docs	Ready	Preview	Comment	Dec 9, 2025 5:36pm

[Copilot]

Pull request overview

This pull request unifies the handling of widget state, buffers, and buffer paths in the anywidget integration, introducing a standardized "wire format" ({state, bufferPaths, buffers}) for transmitting data between Python backend and TypeScript frontend. The changes improve type safety, fix binary data transmission errors, and add comprehensive test coverage for the new encode/decode functions.

Key Changes

• Introduced wire format with explicit encode_to_wire() and decode_from_wire() functions in both Python and TypeScript to standardize binary buffer handling
• Updated anywidget class to use wire format internally while exposing decoded state to users via the value property
• Added extensive test coverage for wire format encoding/decoding, including round-trip tests and edge cases

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
marimo/_plugins/ui/_impl/from_anywidget.py	Added wire format types and encode/decode functions; updated anywidget class to use wire format internally
marimo/_plugins/ui/_impl/anywidget/init.py	Registered message handler for proper buffer handling
marimo/_runtime/runtime.py	Added logging for function call exceptions
tests/_plugins/ui/_impl/test_anywidget.py	Updated tests for wire format and added comprehensive TestWireFormat test class
marimo/_smoke_tests/anywidget_examples/scatter.py	Added new smoke test for jupyter-scatter widget
frontend/src/utils/data-views.ts	Implemented wire format serialization/deserialization with DataView handling
frontend/src/utils/__tests__/data-views.test.ts	Added comprehensive tests for wire format functions including immutability tests
frontend/src/utils/json/base64.ts	Added binaryToByteString utility function
frontend/src/plugins/impl/anywidget/model.ts	Updated Model class to handle wire format; changed dirty fields tracking to use Map
frontend/src/plugins/impl/anywidget/__tests__/model.test.ts	Updated tests to match new wire format and dirty fields behavior
frontend/src/plugins/impl/anywidget/AnyWidgetPlugin.tsx	Updated plugin to decode wire format and serialize changes back to wire format
frontend/src/plugins/impl/anywidget/__tests__/AnyWidgetPlugin.test.tsx	Updated tests to match new wire format

Comments suppressed due to low confidence (1)

marimo/_runtime/runtime.py:1995

• This assignment to 'error_title' is unnecessary as it is redefined before this value is used.
  This assignment to 'error_title' is unnecessary as it is redefined before this value is used.
  This assignment to 'error_title' is unnecessary as it is redefined before this value is used.
  This assignment to 'error_title' is unnecessary as it is redefined before this value is used.

        error_title, error_message = "", ""

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