Support experimental schema types in codegen

[stephentoub]

Schema definitions can now carry experimental stability independently of RPC methods, but the SDK generators only propagated experimental markers from methods. This adds schema-level experimental handling so generated types surface the same non-stable signal as experimental APIs.

Summary

• Add a shared isSchemaExperimental helper for schema stability: "experimental" checks.
• Thread schema experimental metadata through the TypeScript, C#, Python, Go, and Rust generators.
• Emit language-appropriate experimental markers: C# [Experimental(Diagnostics.Experimental)], TypeScript @experimental, Python/Go comments, and Rust doc warnings.
• Move the C# experimental diagnostic ID into the SDK namespace so generated RPC and session-event types can reference it without cross-namespace generated usings.
• Regenerate affected outputs against the repo-imported schema.

Validation

• cd scripts\codegen && npm run generate
• cd dotnet && dotnet build .\src\GitHub.Copilot.SDK.csproj --no-restore --verbosity quiet
• cd go && go build ./...
• cd nodejs && npx tsc --noEmit
• cd python && python -c "import copilot"
• cd rust && cargo check --features test-support

[Copilot]

Pull request overview

Updates the multi-language code generators to treat JSON Schema definitions marked with stability: "experimental" as experimental independently of RPC method stability, ensuring generated types surface appropriate experimental warnings/annotations across SDKs.

Changes:

• Add a shared isSchemaExperimental helper and thread schema-level experimental metadata through TypeScript, C#, Python, Go, and Rust generators.
• Emit language-appropriate experimental markers on generated types (JSDoc/attributes/comments/rustdoc warnings).
• Move the C# Diagnostics.Experimental constant out of generated RPC code into the SDK namespace for reuse by generated outputs.

Show a summary per file

File	Description
scripts/codegen/utils.ts	Adds isSchemaExperimental helper for schema-level stability detection.
scripts/codegen/typescript.ts	Annotates generated TS types as @experimental when definitions or method shapes are experimental.
scripts/codegen/rust.ts	Adds rustdoc experimental warnings for experimental schemas and adjusts generator CLI arg handling.
scripts/codegen/python.ts	Adds experimental comments for generated Python enums/classes/unions and RPC type annotation.
scripts/codegen/go.ts	Adds experimental comments for generated Go enums/types and session-event surfaces.
scripts/codegen/csharp.ts	Propagates schema experimental markers into generated C# attributes and centralizes attribute strings.
rust/src/generated/rpc.rs	Regenerated Rust RPC output (import split reflects generator changes).
dotnet/src/Types.cs	Introduces Diagnostics.Experimental constant in GitHub.Copilot.SDK namespace.
dotnet/src/Generated/Rpc.cs	Removes the generated Diagnostics helper (now sourced from Types.cs).

Copilot's findings

• Files reviewed: 7/8 changed files
• Comments generated: 1

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[github-actions]

Cross-SDK Consistency Review ✅

This PR threads experimental schema-level annotations through all five SDK code generators (TypeScript, C#, Python, Go, Rust) consistently. Here's a summary of the cross-language findings:

Coverage across generators

Generator	isSchemaExperimental on structs/types	On enum types	On discriminated unions	On event data types	On event type constants/classes
TypeScript	✅	✅	✅	✅ (via definition scan)	✅
C#	✅	✅	✅	✅ (dataExperimental)	✅ (eventExperimental)
Go	✅	✅	✅	✅ (dataExperimental)	✅ (eventExperimental)
Python	✅	✅	✅	✅ (via emitPyClass)	✅ (eventExperimental)
Rust	✅	✅	✅	✅ (dataExperimental)	✅ (eventExperimental)

One minor observation

In scripts/codegen/python.ts, PyEventVariant.dataExperimental is set in extractPyEventVariants but never directly consumed — the Python generator achieves the same result because emitPyClass independently calls isSchemaExperimental(schema). This is functionally correct but leaves dataExperimental as a dead field, unlike the C#/Go/Rust generators which reference it explicitly. I've left an inline comment with options to clean this up.

Idiom consistency

Language-specific markers are appropriately idiomatic:

• C#: [Experimental(Diagnostics.Experimental)] attribute
• TypeScript: /** @experimental */ JSDoc
• Go: // Experimental: ... doc comment prefix
• Python: # Experimental: ... comment
• Rust: <div class="warning"> rustdoc warning block

The refactoring of the C# Diagnostics class from the generated Rpc.cs into Types.cs (hand-authored SDK namespace) is a good move that removes a coupling between generated and hand-authored code.

Overall this PR maintains strong cross-SDK parity. 👍

Generated by SDK Consistency Review Agent for issue #1267 · ● 1.4M · ◷

[github-actions]

Generated by SDK Consistency Review Agent for issue #1267 · ● 1.4M