[cpsievert]

Split out of #480; infrastructure for the plotly PR stacked on top of this one. AccessorSpec.opt_in marks accessors whose payloads are unbounded or stream continuously; the renderer skips attaching them at render time, and reading one raises an error pointing at listen_to, unless declared (@render_*(listen_to=["selected"])). listen_to is additive to the always-on accessors, and unknown names raise at decoration time. No accessor is opt-in yet, so this changes no user-visible behavior on its own.

[cpsievert]

@copilot please re-review

[Copilot]

@copilot please re-review

Re-review finding (P2): the new listen_to kwarg in shinywidgets/_render_widget_base.py:114 isn't accepted/forwarded by the explicit constructors for render_embedding_atlas, render_mosaic, or render_quak. For example, render_quak(listen_to=["sql"]) raises TypeError even though sql is a valid always-on accessor. render_mols2grid instead captures it in **kwargs and routes it to widget options, bypassing accessor validation. These constructors should explicitly accept and forward listen_to.

No files changed. Targeted tests could not run because this environment lacks both uv and pytest.

[cpsievert]

@copilot please re-review

[Copilot]

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[Copilot]

@copilot please re-review

Re-reviewed all four commits. The constructor forwarding issue is resolved in c668733, with regression tests; no new actionable findings.

CI for c668733 passed all nine jobs. The Python 3.11 log confirms 1,154 tests passed (3 skipped, 1 expected failure). Local tests remain unavailable because uv and pytest aren't installed. No files changed.