Add max_output_tokens to ModelCapabilities limits

[1fanwang]

Summary

TypeScript callers cannot set an output token limit through the session config, even though the wire protocol accepts one. Setting a value fails to compile with TS2561, so the only way to reach the field is to cast away the type.

Problem

The generated RPC schema declares an optional output token limit on the model capabilities override. The hand-written public model capabilities type omits it. The session config override is a deep partial of that public type, so the compiler rejects the field for a value the protocol already accepts.

Solution

Add the optional field to the public limits type, next to the existing prompt token limit, so the public surface matches the generated schema.

Testing Done

Compiled a probe that sets the field on a session config against the base branch and this branch, and ran the repository typecheck gate.

Raw logs

$ printf 'import type { SessionConfig } from "./src/types";\nconst c: SessionConfig = { modelCapabilities: { limits: { max_output_tokens: 8192 } } };\nvoid c;\n' > probe-mot.ts
$ npx tsc --noEmit --skipLibCheck --target es2020 --moduleResolution node probe-mot.ts

# base branch:
probe-mot.ts(2,59): error TS2561: Object literal may only specify known properties, but
'max_output_tokens' does not exist in type '{ max_prompt_tokens?: number; ... }'.
Did you mean to write 'max_prompt_tokens'?

# this branch:
(no output, compiles cleanly)

$ npm run typecheck
> tsc --noEmit && tsc --noEmit -p tsconfig.test.json
(no output, both configs pass)

[Copilot]

🟢 Approval recommended

The focused type change resolves the schema mismatch with no unresolved issues.

Pull request overview

Aligns the public TypeScript model-capabilities type with the generated RPC schema.

Changes:

• Adds optional max_output_tokens support to model capability limits.

File summaries

File	Description
nodejs/src/types.ts	Exposes the existing wire-protocol output-token limit in the public type.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced

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[SteveSandersonMS]

Confirmed: the generated RPC schema (ModelCapabilitiesOverrideLimits) already declares max_output_tokens, and this field is already present in the hand-written public wrapper types for Python, Rust, Java, Go, and .NET — Node's ModelCapabilities was the only one missing it. I reproduced the reported TS2561 compile error locally by reverting this change and confirmed the fix resolves it cleanly. Minimal, correctly-scoped, no further test/doc changes needed. Approving.