docs: cohort synchronisation

[Zaimwa9]

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• I have added information to docs/ if required so people know about the feature.
• I have filled in the "Changes" section below.
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Changes

Contributes to #8420

Adds a Cohort Synchronisation docs category under Third-Party Integrations:

• Overview — how synchronised segments behave (source owns membership, identifier matching, environment scoping, background updates), where to create one, synchronisation keys, and how to delete a segment or revoke access.
• CSV file — preparing the file, creating the segment, and re-uploading to update members (each upload replaces the membership).
• Amplitude — create a synchronisation key, add the Flagsmith cohort destination in Amplitude, then sync a cohort and pick a cadence.

Also updates the connect modal's footer link, which pointed at the generic segments docs, so Amplitude links to its own page and Mixpanel to the category overview.

Mixpanel is intentionally left out of the docs for now and will follow in a separate PR.

How did you test this code?

npm run build in docs/ passes and the Link Check Docs job is green. Screenshots were taken from staging.

[vercel]

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Project	Deployment	Actions	Updated
docs	Ready	Preview	Sep 2, 2026 12:04pm UTC
flagsmith-frontend-staging	Ready	Preview	Sep 2, 2026 12:04pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
flagsmith-frontend-preview	Ignored	Preview	Sep 2, 2026 12:04pm UTC

[coderabbitai]

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ℹ️ Recent review info

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Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Team

Run ID: c8dee571-0baf-4491-ba15-d86fbf24d4f5

📥 Commits

Reviewing files that changed from the base of the PR and between 0d98e99 and 5353ef9.

📒 Files selected for processing (3)

• docs/docs/third-party-integrations/cohort-synchronisation/amplitude.md
• docs/docs/third-party-integrations/cohort-synchronisation/csv-import.md
• docs/docs/third-party-integrations/cohort-synchronisation/index.md

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📝 Walkthrough

Walkthrough

Adds a new Docusaurus category and three pages for cohort synchronisation. The documentation covers Amplitude synchronisation, CSV import, segment membership replacement, synchronisation keys, and access revocation. Updates CohortProviderConfig with a required docsUrl field. Adds provider-specific URLs for Amplitude and Mixpanel. Updates the connection modal to use the configured URL and new link text.

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

Merge Risk: ⚪ Minimal · up to 5353e

This change adds cohort synchronisation documentation and updates provider help links; no actionable merge-blocking risk remains after normal checks and review.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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[Zaimwa9]

@matthewelwell @gagantrivedi would love your feedback on the docs (CSV and Amplitude), available from the vercel docs deployment

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-8425	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-8425	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-8425	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-8425	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api:pr-8425	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-8425	Finished ✅	Results ✅

[github-actions]

✅ private-cloud · depot-ubuntu-latest-arm-16 — run #20060 (attempt 1)

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

 3 passed

Details

 3 tests across 3 suites
 39.1 seconds
 5353ef9
 🔄 Run: #20060 (attempt 1)

🗂️ Previous results

✅ private-cloud · depot-ubuntu-latest-16 — run #20060 (attempt 1)

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

 2 passed

Details

 2 tests across 2 suites
 48.4 seconds
 5353ef9
 🔄 Run: #20060 (attempt 1)

✅ oss · depot-ubuntu-latest-16 — run #20060 (attempt 1)

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

 1 passed

Details

 1 test across 1 suite
 39.8 seconds
 5353ef9
 🔄 Run: #20060 (attempt 1)

✅ oss · depot-ubuntu-latest-arm-16 — run #20060 (attempt 1)

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

 1 passed

Details

 1 test across 1 suite
 40.4 seconds
 5353ef9
 🔄 Run: #20060 (attempt 1)

✅ private-cloud · depot-ubuntu-latest-arm-16 — run #20059 (attempt 1)

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

 1 passed

Details

 1 test across 1 suite
 1 minute, 12 seconds
 0d98e99
 🔄 Run: #20059 (attempt 1)

✅ private-cloud · depot-ubuntu-latest-16 — run #20059 (attempt 1)

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

 3 passed

Details

 3 tests across 3 suites
 33.2 seconds
 0d98e99
 🔄 Run: #20059 (attempt 1)

✅ oss · depot-ubuntu-latest-arm-16 — run #20059 (attempt 1)

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

 1 passed

Details

 1 test across 1 suite
 38 seconds
 0d98e99
 🔄 Run: #20059 (attempt 1)

✅ oss · depot-ubuntu-latest-16 — run #20059 (attempt 1)

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

 1 passed

Details

 1 test across 1 suite
 34.5 seconds
 0d98e99
 🔄 Run: #20059 (attempt 1)

[github-actions]

Visual Regression

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