omp xd-device: keystone_render crashes bridge on result (`C of e.content`) though render succeeds; docs schema renders as unknown; wrong-key error opaque

[rz1989s]

Environment

• omp 18.1.12 (homebrew, darwin-arm64), keystone@1.0.0 at ~/.omp/plugins/node_modules/@getpipher/keystone
• Device: xd://keystone_render

Repro

1. read xd://keystone_render → docs show type Args = unknown — the extension's parameters (htmlPath/url/viewports/outDir) never surface, so the agent must guess keys.
2. Write {"path": "/tmp/x.html", "viewports": [1280]} (natural guess) → error: The "path" argument must be of type string. Received undefined. Raw Node fs error from pathToFileURL(input.htmlPath); doesn't name the expected key htmlPath.
3. Write {"htmlPath": "/tmp/x.html", "viewports": [1280], "outDir": "/tmp/out"} → render succeeds (all artifacts written: computed.json, dom.html, viewports.json, clickable.json, screenshot-*.png) but the device returns error: undefined is not an object (evaluating 'C of e.content').

Expected

• Docs echo the declared parameter schema.
• Wrong keys → schema-echo error naming htmlPath.
• Successful render → tool result with screenshots/computedStylesPath/viewportMetrics, not a crash.

Actual analysis

extensions/render.ts omp registration returns the plain RenderOutput object from execute(_toolCallId, input). The omp xd bridge appears to expect a message-like {content: [...]} result and dereferences .content of something undefined (minified C of e.content), surfacing a successful render as an error. Callers can't get viewportMetrics from the tool response at all — only by reading the written viewports.json.

Workaround

Pass outDir explicitly and read the artifacts from disk; ignore the error if the outDir is populated.

Related: #13 (pi-side definition.execute is not a function — same registration area, pi copy now uses run(input) while the omp copy uses execute(_toolCallId, input)).