[Core] Add Factory Pause Checkpoints

[MRayermannMSFT]

What

Adds token-scoped factory pause and durable checkpoint APIs to the Node.js SDK after the runtime contract lands. A paused attempt settles its waiter while resume preserves invocation limit overrides and execution identity.

Why

Factory authors need a safe checkpoint that stops spend without losing completed work. Token-scoped aborts stop an old attempt from cancelling a resumed attempt with the same run ID.

[Copilot]

Copilot review overview

🟡 Changes recommended

Public factory documentation remains inconsistent with resumable paused runs, and one new error message is malformed.

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Review tier: Balanced
Findings: 2

Open findings (2)

• Update public guidance for resumable paused runs · New
• Fix the malformed factory guard message · New

What changed in this PR

Adds Node.js factory pause checkpoints, resumable pause semantics, token-scoped cancellation, and nullable invocation-limit overrides.

Changes:

• Adds public and contextual pause APIs.
• Scopes aborts to execution tokens.
• Adds pause, resume-limit, and cancellation tests.

File	Description
nodejs/​src/​session.ts	Implements pause checkpoints and token-scoped aborts.
nodejs/​src/​factory.ts	Defines pause and limit-override APIs.
nodejs/​src/​index.ts	Exports the limit-override type.
nodejs/​test/​factory.test.ts	Tests pause, resume, and abort behavior.

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[github-actions]

SDK Consistency Review

Scope of PR #2537: All 6 changed files are within nodejs/ only:

• nodejs/docs/factories.md
• nodejs/src/factory.ts
• nodejs/src/index.ts
• nodejs/src/session.ts
• nodejs/test/e2e/factory.e2e.test.ts
• nodejs/test/e2e/fixtures/factory-extension.mjs
• nodejs/test/factory.test.ts

What changed: This PR extends the "Agent Factories" API by adding a pause() checkpoint mechanism (ctx.pause(key), SessionFactoryApi.pause(runId), a new paused terminal-ish run status), and renames the FactoryLimits type to FactoryLimitOverrides for clarity.

Cross-SDK check: I verified that the Agent Factories API (session.factory.*, FactoryRunResult, FactoryContext, etc.) does not exist in any other language SDK — Python (python/copilot/), Go (go/), .NET (dotnet/src/), Java (java/sdk/src/main/java/), and Rust (rust/src/) all have no factory-related public API surface. The feature's own documentation (nodejs/docs/factories.md) states it is experimental, and it appears to have been introduced Node-only from its initial commit.

Conclusion: ✅ No cross-SDK consistency issue. Since Agent Factories is currently a Node.js-only experimental feature, extending it further in Node.js alone does not create a parity gap — there is no equivalent surface in other SDKs to keep in sync with. Naming (pause, paused, FactoryLimitOverrides) and structure are consistent with existing conventions already used in factory.ts (e.g., cancel/cancelled, resume). No action needed for other language SDKs at this time.

Generated by SDK Consistency Review Agent for #2537 · copilot · sonnet50 · 40.1 AIC · ⌖ 12.2 AIC · ⊞ 8.3K · ◷