Infer defineTool handler args from parameters schema

[Copilot]

Daily rig evaluation surfaced a recurring defineTool usability failure: handlers that destructure args required duplicate explicit generics despite parameters already carrying type information. This change makes defineTool infer handler arg types from rig s.* schemas while preserving existing behavior for tools without parameters and plain JSON Schema configs.

• API typing update

  • Added a schema-aware defineTool overload that maps parameters to handler arg types via InferSchema.
  • Kept a fallback overload so existing calls like defineTool("x", { handler }) and explicit generic usage continue to typecheck.

• Regression coverage

  • Updated tool-definition tests to validate inferred destructured handler args without manual annotation.
  • Added a type-level assertion that inferred tool types match expected handler arg shape.

• Docs clarity

  • Updated README.md and skills/rig/SKILL.md to document:
    • inference when using rig s.* schemas
    • explicit generic guidance for plain JSON Schema

const lookupIssue = defineTool("lookup_issue", {
  parameters: s.object({ issue: s.string }),
  handler: async ({ issue }) => `Issue ${issue}`, // issue inferred as string
});

// For plain JSON Schema:
const tool = defineTool<{ issue: string }>("lookup_issue", {
  parameters: { type: "object", properties: { issue: { type: "string" } } },
  handler: async ({ issue }) => `Issue ${issue}`,
});

• Fixes [rig-tasks] Daily rig evaluation — 2026-07-23 — 5/5 passed #67