fix(core): preserve per-tool argument type inference in provideExperimentalWebMcpTools - #70159

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Fixes #70125

What is the current behavior?

provideExperimentalWebMcpTools declares a single generic InputSchema for the whole ToolDescriptor<InputSchema>[] array. Because the entire array shares one InputSchema, TypeScript unifies the inputSchema types when multiple tools with heterogeneous inputs are provided, and the execute callback arguments degrade to unknown / Record<string, unknown> (the reporter observed number | { [x: string]: unknown }), breaking type safety inside execute.

This is the well-known TS limitation from microsoft/TypeScript#14466: a single generic cannot be inferred independently per array element.

What is the new behavior?

Each tool now infers its own InputSchema from its own inputSchema property. The parameter type is a tuple-mapped type ({ [K in keyof InputSchemas]: ToolDescriptor<InputSchemas[K]> } over const InputSchemas extends readonly JsonSchemaForInference[]) so every execute callback receives precisely-typed arguments: args.arg1 is number for a { type: 'number' } schema, args.arg2 is string, etc. The function body is unchanged (it only iterates the tools), and the existing call shape provideExperimentalWebMcpTools([...]) is preserved.

Existing call sites remain backward compatible. Verified against the patterns used in the current runtime spec (packages/core/test/webmcp/provide_tools_spec.ts), pre-typed ToolDescriptor<JsonSchemaForInference>[] arrays, and the provideExperimentalWebMcpTools<any>(...) workaround from the issue.

The public API golden (goldens/public-api/core/index.api.md) was updated to the new signature.

Does this PR introduce a breaking change?

• Yes
• No (type-level change only; all existing homogeneous call sites compile unchanged)

Verification

• Added a compile-time regression spec at packages/core/test/strict_types/mcp_tools_spec.ts (the repo's strict-types test target, which compiles under strict: true). With the old signature the spec fails to compile (arg1 / arg2 resolve to unknown); with the fix it compiles and the jasmine test passes.
• pnpm bazel test //packages/core/test/strict_types:strict_types passes with the fix applied.

Notes

• This is a type-level fix with no runtime behavior change; WebMCP remains experimental.
• There are no other open pull requests from this author in angular/angular.
• If the API golden needs regenerating, pnpm public-api:update produces it deterministically.