[backryun]

What changed

• Validate nested Kie task results as JSON objects before reading transcription fields.
• Preserve the supported response.text → resultText → nested text → top-level text fallback order.
• Add an end-to-end handler test for all four envelopes, including a malformed earlier field.

Why

KieExecutor.pollTask() returns a generic JSON object whose nested values remain unknown.
The transcription handler read those nested values directly, producing three TS2339 diagnostics
under both TypeScript 6 and native TypeScript 7. It could also return a non-string value when an
earlier field had an unexpected shape.

Impact

The request and successful-response shapes are unchanged. Kie speech-to-text responses now
guarantee a string text value and continue to a later supported envelope when an earlier value
is malformed.

Validation

• Re-measured on release/v3.8.49 at b4776a2d8 with a complete line-number-agnostic diagnostic diff:
  • TypeScript 6: 131 → 128; 3 fixed, 0 new
  • native TypeScript 7: 130 → 127; 3 fixed, 0 new
• Audio transcription tests: 25/25 passing
• Core typecheck passing
• Focused ESLint passing
• check:file-size, T11 any-budget, Prettier, and git diff --check passing

Tracking: #8484