[Connor Peet (connor4312)]

Adds optional resultMetadata?: Record<string, unknown> to ToolCallResult, mirroring the _meta field of MCP CallToolResult (the same way structuredContent mirrors MCP structuredContent).

Why

MCP Apps read app-only data from a tool result's _meta. Hosts that rebuild an MCP App tool result from AHP state (e.g. when a session is reopened or restored) had nowhere to keep it. ToolCallBase._meta is host/provider metadata (ui, toolKind, ...), so putting server-controlled data there risks collisions. Without the result metadata, restored MCP App cards lose their data: microsoft/vscode#343243.

Changes

• types/channels-chat/state.ts: new optional ToolCallResult.resultMetadata.
• types/channels-chat/reducer.ts: the result-confirmation path copies resultMetadata alongside structuredContent. The native Swift, Rust, Kotlin, Go and .NET reducers do the same.
• Reducer fixtures updated, plus a new pending-confirmation reducer case and a round-trip fixture.
• Regenerated schemas and all client state models. Change fragment added (additive, non-breaking).

Consumers

• agentHost: preserve MCP App tool-result _meta for restored cards vscode#344856 mirrors this field in VS Code's synced types and uses it for MCP App result reconstruction.
• github/copilot-agent-runtime#30458 supplies the MCP result _meta from the Copilot runtime.

Validation

• npm run generate: all targets regenerated.
• npm test: typecheck, lint, release-metadata, changelog/fragment and generated-freshness checks pass; types/reducers.ts coverage is 100%.
• Locally on Windows, scripts/read-window-exempt.test.ts and types/channel-delivery.test.ts fail ("Control Messages section must exist"). They fail the same way on unmodified main with core.autocrlf=true, so this change doesn't cause them.

_{Written by Connor's agent}