fix: queue membership count refreshes for cohort segments

[gagantrivedi]

• I have read the Contributing Guide.
• I have added information to docs/ if required so people know about the feature.
• I have filled in the "Changes" section below.
• I have filled in the "How did you test this code" section below.

Changes

Closes #8268.

Cohort segments never showed membership counts: cohort creation bypasses the segment serializer (where refreshes are queued), and cohort membership is the one way segment members change without a segment or identity edit.

• create_cohort queues a membership refresh after creating its managed segment.
• Membership deltas deliberately do not queue refreshes — the recount is an expensive per-project ClickHouse scan and delta volume is unbounded; changed counts pick up on the recurring refresh cycle.

The blocking prerequisite in #8268 (system traits missing from the ClickHouse identities mirror) shipped in edge-api and was verified end to end on staging: cohort member add/remove now moves the segment's membership count.

How did you test this code?

Unit tests for both call sites. The pipeline (CDC → ClickHouse → count) verified manually against staging.

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[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-e2e:pr-8438	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api-test:pr-8438	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-8438	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api:pr-8438	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-8438	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-8438	Finished ✅	Results ✅

[coderabbitai]

📝 Walkthrough

Walkthrough

create_cohort now queues a project membership refresh when CLICKHOUSE_ENABLED is active. A unit test verifies this call. The observability catalogue updates source line references for seven cohort events.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🟡 Moderate · up to db42c

Cohort creation now schedules an asynchronous membership-count refresh, but the refresh can run before the cohort and managed segment are committed, leaving counts stale or incomplete. The PR should defer scheduling until transaction commit before merging.

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[github-actions]

✅ private-cloud · depot-ubuntu-latest-arm-16 — run #20051 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-arm-16)

 3 passed

Details

 3 tests across 3 suites
 1 minute, 2 seconds
 5177aef
 🔄 Run: #20051 (attempt 1)

🗂️ Previous results

✅ private-cloud · depot-ubuntu-latest-16 — run #20051 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-16)

 4 passed

Details

 4 tests across 4 suites
 57.7 seconds
 5177aef
 🔄 Run: #20051 (attempt 1)

✅ oss · depot-ubuntu-latest-arm-16 — run #20052 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 1 passed

Details

 1 test across 1 suite
 40.9 seconds
 db42c76
 🔄 Run: #20052 (attempt 1)

✅ oss · depot-ubuntu-latest-16 — run #20052 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-16)

 1 passed

Details

 1 test across 1 suite
 41.8 seconds
 db42c76
 🔄 Run: #20052 (attempt 1)

✅ oss · depot-ubuntu-latest-arm-16 — run #20051 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 1 passed

Details

 1 test across 1 suite
 40.5 seconds
 5177aef
 🔄 Run: #20051 (attempt 1)

✅ oss · depot-ubuntu-latest-16 — run #20051 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-16)

 1 passed

Details

 1 test across 1 suite
 40.5 seconds
 5177aef
 🔄 Run: #20051 (attempt 1)

✅ private-cloud · depot-ubuntu-latest-16 — run #20049 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-16)

 1 passed

Details

 1 test across 1 suite
 56.5 seconds
 27883eb
 🔄 Run: #20049 (attempt 1)

✅ private-cloud · depot-ubuntu-latest-arm-16 — run #20049 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-arm-16)

 2 passed

Details

 2 tests across 2 suites
 38.3 seconds
 27883eb
 🔄 Run: #20049 (attempt 1)

✅ oss · depot-ubuntu-latest-arm-16 — run #20049 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 2 passed

Details

 2 tests across 2 suites
 24.9 seconds
 27883eb
 🔄 Run: #20049 (attempt 1)

✅ oss · depot-ubuntu-latest-arm-16 — run #20050 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 1 passed

Details

 1 test across 1 suite
 48.3 seconds
 b3f0136
 🔄 Run: #20050 (attempt 1)

✅ oss · depot-ubuntu-latest-16 — run #20050 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-16)

 1 passed

Details

 1 test across 1 suite
 41.7 seconds
 b3f0136
 🔄 Run: #20050 (attempt 1)

✅ oss · depot-ubuntu-latest-16 — run #20049 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-16)

 1 passed

Details

 1 test across 1 suite
 34.2 seconds
 27883eb
 🔄 Run: #20049 (attempt 1)

[github-actions]

Visual Regression

19 screenshots compared. See report for details.
View full report

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.81%. Comparing base (894bfa4) to head (db42c76).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8438   +/-   ##
=======================================
  Coverage   98.81%   98.81%           
=======================================
  Files        1621     1621           
  Lines       66118    66128   +10     
=======================================
+ Hits        65334    65344   +10     
  Misses        784      784           

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[coderabbitai]

Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Team

Run ID: 9cfb2695-c676-4a49-9ee4-ce25278aa705

📥 Commits

Reviewing files that changed from the base of the PR and between 76da16c and db42c76.

📒 Files selected for processing (3)

• api/cohorts/services.py
• api/tests/unit/cohorts/test_services.py
• docs/docs/deployment-self-hosting/observability/_events-catalogue.md

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