(MOT-4519) feat(console): preview screen renders agent HTML beside the chat

[rohitg00]

Why

A workspace column shows chat, traces, workers, or ext:<worker-page>. There was no way for an agent to show its own HTML — a plan, a chart, a rendered diff — in the workspace. This is the most-cited use of the browser-in-terminal tools that motivated the workspace functions: write a page, open it beside the conversation.

What

A preview:<path> screen kind.

• Rust (console/src/functions/workspace.rs): is_valid_screen accepts preview:<path> (non-empty), so console::workspace::open screen=preview:/path/to/plan.html places it beside chat like any screen and it persists in the layout. The function description names it.
• TS (workspace-tabs.ts): previewPathForScreen / screenForPreview, validation, and a basename label.
• PreviewPane (pages/Preview): reads the file through shell::fs::read and renders it in a sandboxed iframe (sandbox="", so page scripts never run and it cannot reach the console around it). HTML/SVG render as a document; other text renders as preformatted text. Nothing is stored in the polled console config — the path travels in the screen id and the bytes are read on demand, so history and previews never bloat the config the way inlined blobs would.

Verification

• cargo fmt --check, cargo clippy -D warnings, cargo test (console; screen_validation covers preview:<path> and rejects a bare preview:).
• tsc -b, biome, vitest 1472 (preview round-trip, label, and that a malformed preview: tab is dropped).
• Rig: built and installed. console::workspace::open screen=preview:/…/preview-demo.html returned placement: new_column, console::workspace::list shows ['chat', 'preview:/…/preview-demo.html'], and the column renders the agent's HTML in the sandboxed iframe.

Stacked on #861 → #860 → #843. Merge those first.

Linear: MOT-4519

[vercel]

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Project	Deployment	Actions	Updated (UTC)
workers	Ready	Preview	Aug 20, 2026 3:53pm
workers-tech-spec	Ready	Preview	Aug 20, 2026 3:53pm

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[github-actions]

skill-check — worker

0 verified, 62 skipped (no docs/).

Layer	Result
structure	✓
vale	✓
ai	✓
render	✓

Four for four. Nicely done.

[rohitg00]

Superseded: preview: is the cheap version of a proper agent-artifact primitive (durable, addressable, shareable, versioned — like Claude Code artifacts). Closing in favor of that direction.