Fix Cypress crossfade/gapless failures: keep playback_session in the earliest event batch

[osmestad]

Why

After #697 merged, the Cypress case-crossfade.cy.ts and case-gapless.cy.ts specs started failing on every open PR (expected 2 playback_session events, got 1). The specs never ran on #697 itself because it was stacked on the #696 branch and the Cypress workflow only triggers for PRs targeting main.

Root cause: the event sender dispatches at most 10 events per request (SQS batch limit), and the two specs asserted on the first intercepted batch only. A crossfade/gapless run produces enough events that the second track's playback_session sat exactly at the 10-event batch boundary. The event enqueue-timing changes in #697 (serialized reducers, actual-start reporting) shifted the order so it fell into the second batch — which the specs never looked at.

What

• BasePlayer.eventTrackingStreamingEnded now enqueues playback_session before the session's own playback_statistics/streaming_session_end events, so the consumption-relevant play_log event is never bumped to a later batch by its own session's metrics events.
• The crossfade and gapless specs now aggregate events across all intercepted event requests (retrying until a later batch arrives if needed) instead of asserting on the first request only, and include the seen event names in the assertion message for easier diagnosis.

Verified

• pnpm --dir packages/player typecheck and lint:ci pass locally.
• Cypress runs in CI on this PR (could not be run locally — requires the CI test-user secret).

Made with Cursor

[Copilot]

Pull request overview

This PR addresses Cypress flakiness/regressions in the crossfade and gapless play-log specs by ensuring playback_session events are dispatched early enough to land in the earliest event batch, and by updating the specs to assert across all intercepted event batches (not just the first request).

Changes:

• Reordered end-of-session event sending so playback_session is committed before the session’s streaming-metrics end events.
• Updated crossfade/gapless Cypress specs to aggregate events across all intercepted event requests and include better assertion diagnostics.
• Documented the behavioral change in the player changelog.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/player/src/player/basePlayer.ts	Ensures playback_session is committed before auxiliary streaming-metrics events on session end to stabilize earliest-batch ordering.
packages/player/cypress/e2e/play-log/case-gapless.cy.ts	Aggregates events across all intercepted requests and retries until both playback_session events are observed.
packages/player/cypress/e2e/play-log/case-crossfade.cy.ts	Same aggregation/retry strategy as gapless to avoid asserting on only the first batch.
packages/player/CHANGELOG.md	Notes the updated enqueue/dispatch ordering for playback_session vs. streaming-metrics end events.

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