feat(platform): forward events the SDK doesn't know to onEvent

[amitbardos]

Stacked on #313 (base amitb/platform-asyncapi-sync).

This changes the original event filtering Oz (@ozsay) wrote, so it needs his agreement before merging.

What

Today the builder session registers a Socket.IO handler only for the event names generated into the SDK, so a new backend event is dropped until a partner upgrades. Now:

• Known app events keep their own handlers, unchanged.
• socket.onAny forwards any other name to onEvent, except session events (app.snapshot, session.ended) and room.* notices (a new notice has no error code, so it's still dropped).
• Same {room, data} envelope validation, per-app routing and protocol_error handling as known events. discard() now also calls offAny().
• Unknown events arrive as a new PlatformEvent member: { type: "unknown"; name: string; appId: string; data: Record<string, unknown> }.

Why type: "unknown" and not type: string

The original plan was an OtherToolCall-style member with type: string & {}. In TypeScript 5.9 that breaks narrowing for every known event: with string & {}, event.type === "message.updated" doesn't narrow at all. With plain string it narrows to that event plus the catch-all, so event.data.message becomes unknown. Either way existing partner code like event.data.message.content stops compiling. A literal "unknown" discriminant keeps known types narrowing exactly. It can't clash with a real event because backend event names are always dotted (noun.verb). The name goes in name. Once a partner upgrades, the event arrives under its own type.

This is a type-level breaking change (an exhaustive switch needs case "unknown"), so it should ship in 0.2.0. It's noted in the CHANGELOG.

Tests

New unit tests: an unknown event reaches only its app's onEvent, known, session and room.* names aren't double-delivered through onAny, a malformed unknown frame fails only its app, and close() calls offAny. New type tests: an unknown event's data needs a check before use, and known types still narrow.

npm test   (packages/platform)
  test:types  tsc --noEmit -p tsconfig.type-tests.json   ✓
  test:unit   Test Files 2 passed (2)   Tests 44 passed (44)
  docs        typedoc   markdown generated at ./docs
  test:package  tests 5  pass 5  fail 0
npm run check:events   builder.events.generated.ts is up to date.
npm run create-docs    ✓ Post-processing complete!
npm run lint (root)    eslint .   clean

🤖 Generated with Claude Code

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🚀 Package Preview Available! (@base44/platform)

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{
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