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3ccf2a0739
Adds client-capability-gated tool availability: gateway clients declare capabilities at connect (new inline-widgets cap), chat.send stamps them into the run context, and every tool assembly path (embedded runner, queued followups, Codex app-server harness, plugin-only construction plans) drops tools whose requiredClientCaps the originating client did not declare. The Canvas plugin ships the first such tool, show_widget: agents pass SVG or an HTML fragment plus a title; the plugin hosts it as a bounded, retention-scoped Canvas document and returns the existing canvas preview handle, which web chat renders as a sandboxed iframe fitted to the widget's reported content height. Widget frames never get allow-same-origin (per-preview sandbox ceiling, including the sidebar path) and the Canvas host serves widget documents with a CSP sandbox header so direct navigation runs in an opaque origin. Verified live end-to-end on a Testbox with gpt-5.5 (screenshots on the PR). CLI-backed model backends do not carry client caps yet and stay fail-closed (#102577). Closes #101790
45 lines
2.9 KiB
Markdown
45 lines
2.9 KiB
Markdown
---
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summary: "Render self-contained SVG or HTML widgets inline in web chat"
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title: "Show widget"
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sidebarTitle: "Show widget"
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read_when:
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- You want an agent to render an interactive result inside web chat
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- You need the show_widget input, security, or retention contract
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---
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`show_widget` renders a self-contained SVG or HTML fragment inline in the Control UI chat transcript. The bundled Canvas plugin owns the tool and hosts each result as a same-origin Canvas document.
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The tool is available only when the originating Gateway client declares the `inline-widgets` capability. The Control UI declares this capability automatically. Channel runs such as Telegram and WhatsApp do not receive `show_widget`.
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Capability transport currently covers the embedded runner and the Codex app-server backend. CLI-backed model backends do not yet carry client capabilities, so capability-gated tools stay unavailable (fail closed) on those backends.
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## Use the tool
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The agent supplies two required strings:
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<ParamField path="title" type="string" required>
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Short title shown with the inline preview and in the hosted document title.
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</ParamField>
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<ParamField path="widget_code" type="string" required>
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Self-contained SVG or HTML fragment. Input beginning with `<svg` after trimming is rendered in SVG mode; all other input is treated as an HTML fragment. Maximum length: 262,144 characters.
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</ParamField>
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The tool result includes a Canvas preview handle, so web chat renders the widget directly from the tool call and restores it after history reload. Transcripts that do not render previews still show the hosted Canvas path.
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## Security and storage
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Widget documents use a restrictive Content Security Policy: inline style and script are allowed, images may use `data:` URLs, and external fetches and resource loads are blocked. Keep all markup, styles, scripts, and image data inside `widget_code`.
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The iframe always omits `allow-same-origin`, even when the Control UI's global embed mode is `trusted`, so widget scripts cannot read the parent application origin. The Canvas host also serves widget documents with a `Content-Security-Policy: sandbox allow-scripts` response header, so opening the hosted URL directly still runs the widget in an opaque origin instead of the Control UI origin. Browser sandboxing does not prevent a script from navigating its own iframe; only render widget code you are willing to execute in that isolated frame.
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The iframe also follows [`gateway.controlUi.embedSandbox`](/web/control-ui#hosted-embeds). The default `scripts` tier supports interactive widgets while preserving origin isolation.
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Canvas retains at most 32 widgets per session (or per agent when no session is available). Creating another widget removes the oldest document in that scope.
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## Related
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- [Control UI hosted embeds](/web/control-ui#hosted-embeds)
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- [Canvas plugin](/plugins/reference/canvas)
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- [Gateway protocol client capabilities](/gateway/protocol#client-capabilities)
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