[SDK/Factories] Add argsSchema To The Factory Authoring Surface - #2315

What

FactoryMeta now declares an optional argsSchema, so an extension author can state the argument shape their factory expects.

It reuses the existing FactoryJsonSchema type. That type already documents the same bounded subset the CLI enforces, and the runtime's own validator points at it as the contract boundary.

The field already crossed the wire, because defineFactory snapshots meta whole rather than cherry-picking fields. This change is additive and type-level. It makes an existing runtime feature discoverable to authors writing against the published types.

Docs and JSDoc now describe what a declaration enforces, matching the run_factory tool description word for word.

Why

Almost no factory declares an argument shape, because the SDK never exposed the field. Authors reading the published types cannot tell the feature exists.

That has a real cost. Without a declared schema nothing validates a caller's args. A malformed call starts a run, takes a user approval, spends credits, and then dies inside the factory body with a confusing error about a missing property.

With a declared schema the CLI catches the mismatch before the run starts. The model gets a correction hint and retries. No run row, no permission prompt, no credit spend.

Notes

• nodejs/src/types.ts is hand-written, not generated. It already imports JsonValue from factory.ts, so importing FactoryJsonSchema alongside it follows the established convention.
• No SDK-side shape validation was added. The runtime already rejects an out-of-subset declaration at registration, and duplicating that logic here would risk divergence.
• argsSchema is optional. A factory that omits it behaves exactly as before, which a unit test asserts.
• Enforcement is run_factory-path only. The runtime calls toolRunFactoryValidateArgs from runFactoryTool and nowhere else, so session.factory.run(...) is not validated. The docs and JSDoc say so explicitly, and a doc test pins that caveat, because an author would otherwise reasonably assume their own SDK-initiated runs were checked.

Testing

• New unit test proves a declared argsSchema survives defineFactory, is deep-frozen, serializes to JSON, and reaches the session.resume registration payload. It also asserts an omitting factory carries no such property.
• New doc test pins the SDK wording to the enforced subset and to the tool-path-only caveat, so the SDK and the run_factory tool cannot drift apart.
• The argument-echo E2E fixture declares a schema, proving a declaration registers against a live runtime. It does not prove enforcement, since the E2E drives the SDK path.
• nodejs unit suite, typecheck, lint, and format:check all pass. Three factory.e2e failures are pre-existing and reproduce identically on a clean tree.