[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.

[github-actions]

SDK Consistency Review

This PR modifies only the Node.js/TypeScript SDK (nodejs/src/factory.ts, session.ts, index.ts, generated RPC/session-event types, and the corresponding test file). It adds a new pause() capability to the experimental Agent Factories API (FactoryContext.pause, SessionFactoryApi.pause), renames FactoryLimits → FactoryLimitOverrides, adds a paused terminal-ish run status, and refines the parallel/pipeline helper-scope guard for pause checkpoints.

Cross-SDK check: The "Agent Factories" surface (factory.ts and its defineFactory/FactoryContext/SessionFactoryApi types) currently exists only in the Node.js SDK — there is no equivalent factory wrapper in Python, Go, .NET, Java, or Rust (only Java's generated RPC types under java/sdk/src/generated/... reference factory RPC shapes, but there is no hand-written public API exposing it, consistent with the other languages). Since this feature was already Node.js-only before this PR, adding pause here does not introduce a new parity gap — it's consistent with the existing single-SDK scope of this experimental feature.

No action needed for other SDKs from this PR. If/when Agent Factories is promoted to a stable, multi-language feature, that expansion (including this new pause checkpoint capability) should be tracked as its own cross-SDK effort rather than as a follow-up to this Node-only PR.

No inline consistency issues found; not adding line comments.

Generated by SDK Consistency Review Agent for #2537 · copilot · sonnet50 · 59.3 AIC · ⌖ 12.2 AIC · ⊞ 8.3K · ◷