Adapt selected LLM to governed reasoning

[eamirian]

Summary

• retain a canonical per-call structured result envelope around the already selected ACE LLM route
• report the actual logical provider, resolved model, exact caller-supplied configuration digest, token-unit deltas, and elapsed latency when observed
• represent unavailable provider/model/usage fields explicitly rather than estimating or fabricating them
• adapt the same selected route to the existing Core ReasoningProvider contract with exact context-reference attribution and fail-closed telemetry requirements

Verification

• Ruff check and format: green
• git diff --check: green
• provider, governed-reasoning, Brief synthesis, scheduler, and public-boundary gate: 156 passed

Boundaries

This PR adds no alternate provider route, Builder host composition, setup material, capability state, authority grant, JWT scope, domain vocabulary, MCP change, merge, or release. Provider errors are sanitized, and unknown usage cannot become fabricated zero usage in governed reasoning.