Refine Go SDK pre-GA API surfaces

[qmuntal]

Summary

• refine Go SDK public API shapes for MCP server config, elicitation callbacks, and BYOK model listing
• update generated Go RPC marker casing for initialisms such as MCP/UI
• refresh Go docs and tests for the adjusted surfaces

Breaking changes

• Go: ModelLimits.MaxContextWindowTokens is now optional (*int). Use copilot.Int(value) when constructing ModelInfo values for custom model listing handlers.

Validation

• go test . -run TestSession_ElicitationRequestSchema
• go test ./... -run '^$'

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR strengthens the Go SDK's type model around elicitation and MCP server configuration, replacing loosely-typed map[string]any / string / *[]string shapes with named types and aliases. It also adds a codegen helper for producing Go unexported identifiers that correctly preserve initialism casing (e.g. URL → url, not uRL).

Changes:

• Introduce ElicitationAction, ElicitationSchema, and ElicitationFieldValue types and use them across the SDK, tests, and docs.
• Switch MCPStdioServerConfig.Tools / Args / Env and MCPHTTPServerConfig.Tools / Headers from pointer/omitempty to value/omitzero, and make ModelLimits.MaxContextWindowTokens a *int.
• Add toGoUnexportedIdentifier codegen helper handling initialisms and casing overrides.

Show a summary per file

File	Description
scripts/codegen/go.ts	New helper for unexported identifiers; used for marker names in union emitters.
go/types.go	New elicitation types/aliases; reshape MCP config and ModelLimits fields.
go/session.go	Use new elicitation types; convert ElicitationSchema ↔ RPC schema; tighten toRPCContent nil handling.
go/types_test.go, go/session_test.go, go/client_test.go	Update tests to new types and add schema-conversion test.
go/internal/e2e/*.go	Update e2e tests to new Tools []string and ElicitationAction* constants.
go/README.md, docs/features/mcp.md, docs/auth/byok.md	Update docs to new APIs.

Copilot's findings

Files not reviewed (1)

• go/rpc/zrpc.go: Language not supported

• Files reviewed: 14/15 changed files
• Comments generated: 5