helix.mcp: Skill for Claude Code

Context

Use when adding strict unknown-parameter rejection so callers receive a structured McpException instead of silent data loss when they pass a hallucinated or misspelled parameter name.

Two complementary layers — deploy both for best UX + safety:

• Stage A — SDK-level UnmappedMemberHandling.Disallow (stopgap; no hints)
• Stage B — AddUnknownParameterFilter CallToolFilter (polished UX with "did you mean" hints)

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Stage A — SDK Strict Rejection (Stopgap)

SDK Mechanism

Microsoft.Extensions.AI.Abstractions 10.5.2 (shipped with MCP 1.3.0+) includes a strict check in ReflectionAIFunction.InvokeCoreAsync:

if (SerializerOptions.UnmappedMemberHandling == Disallow && !HasCustomParameterBinding)
    throw ArgumentException(paramName: "arguments",
        message: "The arguments dictionary contains an unexpected key 'X' that does not correspond to any parameter of 'Y'.");

HasCustomParameterBinding is true only when a tool parameter has a non-null BindParameter callback (DI injection). Plain value-type and string params have HasCustomParameterBinding = false → strict check fires.

How to Enable

Pass a JsonSerializerOptions with UnmappedMemberHandling = Disallow and TypeInfoResolver = new DefaultJsonTypeInfoResolver() to WithToolsFromAssembly:

using System.Text.Json.Serialization.Metadata;

.WithToolsFromAssembly(typeof(MyTools).Assembly, new JsonSerializerOptions
{
    UnmappedMemberHandling = JsonUnmappedMemberHandling.Disallow,
    TypeInfoResolver = new DefaultJsonTypeInfoResolver(),  // ← required companion; see below
})

Apply to both HTTP and stdio transport registrations if both are used.

Why TypeInfoResolver is required

AIFunctionFactory.GetOrCreate (in Microsoft.Extensions.AI.Abstractions) calls MakeReadOnly() on the passed JsonSerializerOptions before the tool descriptor is constructed. The constructor then calls AIJsonUtilities.CreateFunctionJsonSchema → CreateJsonSchemaCore, which contains: