.NET: Hyperlight host-tool parameter schemas missing from execute_code descriptions #8446

Parent issue

Sub-issue of #8125. Sibling #8445 is separate and must not close this child or the parent.

Confirmed behavior

At upstream/main 999dda7970fe969c0901d524365ce34ecbda6227, dotnet/src/Microsoft.Agents.AI.Hyperlight/Internal/InstructionBuilder.cs::BuildExecuteCodeDescription emits each host AIFunction name and description but never reads JsonSchema. The model therefore does not receive host-tool parameter names, requiredness, descriptions, enums, or nested shapes through this listing.

Both HyperlightExecuteCodeFunction and HyperlightCodeActProvider use this shared builder. Inspect the standalone function Description or the provider-returned execute-code function description; current BuildInstructions() returns short guidance and is not the correct reproduction accessor.

Acceptance criteria

• Surface existing host-tool parameter schemas in the model-facing execute-code description for both entry points.
• Add parameterized-host-tool regression coverage; the current builder test uses a zero-parameter function and misses the defect.
• Preserve no-tool output, the code-only execute-code input schema, approval behavior, filesystem host-path protection, and network restrictions.
• Keep the fix focused and document directly affected behavior. Confirm rendering and public API choices separately.

Status

Deferred at the user request and outside the sibling PR. This child does not authorize implementation. Source behavior was independently confirmed; no new build or live-model reproduction was run. The parent includes a contributor offer to help, so coordinate ownership and check for an implementing PR before starting.