PR 18813 — Bitbucket continuation through timestamp ties

Tests before takeover: two added regressions across two existing files; 261 focused cases.
Tests after reduction: one added service/provider/API regression in the existing service file; 260 focused cases. All main tests preserved except the intended per-repository cursor and deduplicated serialization expectations. API test file exactly matches pinned main.
Pinned-main production: 257 pass / 3 fail. The new regression receives [] instead of [3,4] on page two; existing assertions also catch the missing internal cursor field and repeated serialized ID.
Fixed: 260 focused cases pass, plus 172 related cases across nine files: total 432 cases across eleven files.
Scoped typecheck, lint, formatting, and diff check pass.

Integration proof uses the real PullRequestService, Bitbucket provider, API query composition, JSON decoding, and limiting. Only external HTTP is mocked. Five PRs at limit two, including three tied at one timestamp and two older, yield pages [1,2], [3,4], [5] and terminate. Existing serialization coverage verifies boundary IDs 3,4 rather than 3,3,4.

Public live API verification on headless Linux:
GET https://api.bitbucket.org/2.0/repositories/atlassian/aui/pullrequests with OPEN/MERGED/DECLINED states, pagelen=2, sort=-updated_on returned HTTP 200 and IDs 5455,5181.
A continuation with q=updated_on <= 2026-10-05T02:55:42.282828+00:00 AND id != 5181 returned HTTP 200 and older IDs 5472,5462, excluding the delivered boundary ID.
This establishes live query acceptance and exclusion behavior. It does not establish a live tied group; that case is integration-test proof above. No authentication or remote mutation was used.

The historical Macroscope claim about batched input is false for this revision. readTogether still forwards only updatedBefore/delivered; only per-repository readRepository forwards seenAt. The named batched regression passes without changing that input expectation.

Not verified: a real authenticated Bitbucket account or live tied group, full UI Load More, macOS, Windows, iOS, Android, Electron desktop. Large exclusion query limits and existing timestamp precision are not redesigned. No wire schema changes or merges.