* feat(canvas): let widget buttons send prompts into web chat
Inline show_widget documents get a sendPrompt(text) bridge: a private
MessageChannel offered to the Control UI before widget code runs. The chat
adopts only the first offer per frame, requires transient user activation,
a visible focused frame, plain text (no slash commands), and rate limits
10 prompts/minute per widget. Accepted prompts run the normal user send
path of the owning chat pane.
* fix(canvas): appease lint/knip/docs gates for widget prompts
Split widget prompt tests into their own file, drive validation and rate
limits through the real port path instead of exported internals, use
addEventListener on the adopted port, and regenerate docs_map.
* fix(canvas): install widget listeners per window for non-isolated tests
Module-boolean listener flags broke in shared vitest workers where each test
file gets a fresh jsdom window; key installation by window instead and give
port flushing more headroom.
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