MCP: emit Gemini-compatible tool schemas (#1074)

[erikdarlingdata]

Problem

Follow-up to #1077. Stateless transport was necessary but not sufficient — Google Antigravity (Gemini) still listed zero MCP tools. @gotqn confirmed by testing the dev build that the remaining blocker is cause #2: parameter schema shape.

A nullable-with-default parameter like string? server_name = null is emitted as:

{ "type": ["string", "null"], "default": null }

Gemini's function-declaration validator rejects union type arrays and the default keyword and drops the entire tool set. Claude Code / opencode are lenient and accept the same schema, which is why this only bites Gemini-based clients.

Fix

Rather than hand-edit ~122 nullable params across the tool classes, transform the schema at registration time.

• PerformanceMonitor.Common/Mcp/McpSchemaCompat.cs — new WithGeminiCompatibleTools<T>(), a drop-in for the SDK's WithTools<T>(). Registers tools identically (same DI service-parameter exclusion and invocation path — mirrors the SDK v1.3.0 WithTools<T> source) but installs a TransformSchemaNode that collapses nullable type unions (["string","null"] → "string") and strips the default keyword.
• Lite/Mcp/McpHostService.cs, Dashboard/Mcp/McpHostService.cs — register every tool class via the new helper.
• PerformanceMonitor.Common.csproj — add the ModelContextProtocol package reference the helper needs.

Behavior is unchanged for lenient clients: optionality is still conveyed by the schema's required array and the .NET default still applies when an argument is omitted — only the wire-format changes.

Test plan

• Lite, Dashboard, and Common build clean (0 warnings / 0 errors)
• Golden-sample tests (3 in Lite.Tests, 3 in Dashboard.Tests) assert against the actual tools/list InputSchema:
  • no union type arrays or default keywords remain
  • the stock WithTools path does still emit them (proves the transform is necessary and guards against SDK drift)
  • the advertised tool set is unchanged (no tools dropped/added)
• Dumped a real transformed schema — the only top-level keys across all tools are type / properties / required; nothing else Gemini-hostile ($schema, additionalProperties, anyOf, …)
• @gotqn to confirm Antigravity lists the tools on the next dev build

🤖 Generated with Claude Code