Stand up unit tests for connector-directline

[AimTune]

packages/connector-directline has zero unit tests today. After the read-tick semantics fix (commit 7a305d0) we rely on manual sandbox verification, which means a future regression won't be caught by CI.

Why this is needed

The fix in 7a305d0 is non-trivial:

• sendMessage emits "sent" synchronously before postActivity resolves.
• The activity stream's echo branch silently consumes nothing — does not touch pendingIds.
• flushPendingToRead() only fires on actual bot message activities (not typing, not events, not the user's own echo).

A naive refactor would easily reintroduce the original "echo → instant double-tick" bug.

Approach

The blocker is mocking botframework-directlinejs. The connector imports DirectLine, ConnectionStatus, and an Activity type from there. The real SDK opens a WebSocket on connect() so it can't run in jsdom directly.

Sketch:

// __tests__/_directLineMock.ts
import { Subject } from "rxjs"; // or hand-rolled minimal Observable

export class FakeDirectLine {
  connectionStatus$ = new Subject<number>();
  activity$ = new Subject<Activity>();
  postActivity = vi.fn(() => of({}));
  end = vi.fn();
}

vi.mock("botframework-directlinejs", () => ({
  DirectLine: vi.fn().mockImplementation(() => new FakeDirectLine()),
  ConnectionStatus: { Online: 2, ExpiredToken: 4, FailedToConnect: 5, Ended: 5 },
}));

Then write tests that:

• Drive activity$.next(...) to simulate echo / typing / message arrivals.
• Assert messageStatusHandler calls in order via vi.invocationCallOrder.

Tests to add

• sendMessage emits "sent" synchronously (before postActivity resolves).
• WebSocket echo of user's own message does not trigger messageStatusHandler.
• First bot message activity flushes every still-pending user id to "read".
• Bot typing activity does not flush — pending stays at "sent".
• Bot event activity (with name) does not flush.
• Send → echo → typing → message keeps "read" order; never downgrades.
• Multiple pending sends: a single bot message flushes all of them at once.

Acceptance criteria

• Tests live in packages/connector-directline/src/__tests__/ and run with pnpm -F @chativa/connector-directline test.
• Tests run in jsdom (no real network).
• Coverage ≥ 70% for the file.

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Spun out of todos.md.