VS Code: respect and format structured JSON outputs

[sethjuarez]

Summary

When running a .prompty file from the VS Code extension, structured JSON outputs should be respected and displayed/formatted as JSON.

Scenario

A prompt can declare structured outputs:

outputs:
  - name: answer
    kind: string
  - name: rememberedPreferences
    kind: array
  - name: staleContextWarning
    kind: string
  - name: nextAction
    kind: string

The model is expected to return structured JSON matching the declared output schema.

Expected behavior

The VS Code extension should:

1. respect the declared outputs schema during execution,
2. treat the result as JSON/structured output when the runtime returns JSON,
3. pretty-print or otherwise format the response as JSON in the result/trace view.

Actual behavior

The extension output appears to display the result as plain text rather than respecting and formatting the JSON output shape.

Why it matters

Structured output is a core Prompty scenario. For authoring/debugging, the VS Code extension should make it obvious when a prompt produced valid JSON and should present that output in a readable, schema-oriented way.