Enable stdio MCP tool and resource method calls

The runtime already framed JSON-RPC initialize traffic over stdio, so this extends the same transport with typed helpers for tools/list, tools/call, resources/list, and resources/read plus fake-server tests that exercise real request/response roundtrips.

Constraint: Must build on the existing stdio JSON-RPC framing rather than introducing a separate MCP client layer
Rejected: Leave method payloads as untyped serde_json::Value blobs | weakens call sites and test assertions
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep new MCP stdio methods aligned with upstream MCP camelCase field names when adding more request/response types
Tested: cargo fmt --manifest-path rust/Cargo.toml --all; cargo clippy --manifest-path rust/Cargo.toml -p runtime --all-targets -- -D warnings; cargo test --manifest-path rust/Cargo.toml -p runtime
Not-tested: Live integration against external MCP servers

rust/crates/runtime/src/lib.rs

@@ -47,7 +47,9 @@ pub use mcp_client::{
 pub use mcp_stdio::{
     spawn_mcp_stdio_process, JsonRpcError, JsonRpcId, JsonRpcRequest, JsonRpcResponse,
     McpInitializeClientInfo, McpInitializeParams, McpInitializeResult, McpInitializeServerInfo,
-    McpStdioProcess,
+    McpListResourcesParams, McpListResourcesResult, McpListToolsParams, McpListToolsResult,
+    McpReadResourceParams, McpReadResourceResult, McpResource, McpResourceContents,
+    McpStdioProcess, McpTool, McpToolCallContent, McpToolCallParams, McpToolCallResult,
 };
 pub use oauth::{
     code_challenge_s256, generate_pkce_pair, generate_state, loopback_redirect_uri,