fix(core): Fix backwards pagination not working if channel was never opened

[VelikovPetar]

Submit a pull request

Linear: FLU-563

Github Issue: #

CLA

• I have signed the Stream CLA (required).
• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request

Backport of master → v9 of commit 1a90e921105fa9edad3985828868fadc22f39d2d (PR #2789, Fixes FLU-563).

The bug

When a user enters a channel with unread_count > 0 but the server-side read state is the "never explicitly read" sentinel (last_read_message_id = null and last_read = 0001-01-01T00:00:00Z — Go's time.Time{} zero value), StreamChannelState._maybeInitChannel unconditionally called loadChannelAtTimestamp(currentUserRead.lastRead).

The backend silently ignores the zero-time created_at_around (via IsZero()) and returns the channel tail. The client then mis-infers boundaries via _inferBoundariesFromAnchorTimestamp: because year-1 precedes every loaded message, it concludes endOfPrependReached: true, sets _topPaginationEnded = true, and backwards pagination is permanently dead on the channel.

The fix

Guard the timestamp branch on currentUserRead.lastRead.isAfter(_minValidLastRead) (DateTime.utc(1970)). When it's the zero sentinel, the code falls through to the existing catch-all — stay on the cached latest window if up-to-date, otherwise reload the latest page.

Adds a _maybeInitChannel test group with four regression guards: idAround for lastReadMessageId, createdAtAround for real timestamps, no query for the Go zero-time case when up-to-date, and a latest-page reload for the Go zero-time case when stale.

Backport notes

• Manual port, not a clean cherry-pick. The _maybeInitChannel logic on v9 was byte-for-byte identical to master's pre-fix state, but v9 and master diverge in analysis_options.yaml: v9 drops the page_width: 120 formatter block (reverting to the 80-col default) and enables the avoid_redundant_argument_values lint. A raw cherry-pick would have imported master's formatting/lint style.
• v9-specific adaptation: master's DateTime.utc(1970, 1, 1) / DateTime.utc(1, 1, 1) are written as DateTime.utc(1970) / DateTime.utc(1) here (semantically identical) to satisfy v9's enabled avoid_redundant_argument_values lint.
• Verified test-first: confirmed the two Go-zero-time tests fail on v9 before the fix, then pass after. dart format, dart analyze --fatal-infos, and all 30 tests in stream_channel_test.dart are green.

Screenshots / Videos

No UI changes. (See the before/after videos on the original master PR #2789.)

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c4fb095e-5927-41ef-aff2-c4ab25177d6b

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch port/master-to-v9/FLU-563_fix-pagination-never-opened-channel

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (v9@f3ceb35). Learn more about missing BASE report.

Additional details and impacted files

@@          Coverage Diff          @@
##             v9    #2812   +/-   ##
=====================================
  Coverage      ?   66.86%           
=====================================
  Files         ?      429           
  Lines         ?    27102           
  Branches      ?        0           
=====================================
  Hits          ?    18121           
  Misses        ?     8981           
  Partials      ?        0           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.