feat(DOC-2012): document Kafka 4.x client compatibility and KIP-890

[mfernest]

Summary

• Explicitly states Kafka 4.x clients (4.0, 4.1) are compatible with Redpanda — tested and confirmed by engineering (ENG-700)
• Adds KIP-890 (Transactions Server-Side Defense) to the unsupported features list: Redpanda does not implement the server-side portion, but Kafka 4.x clients detect this and fall back gracefully to the standard transaction protocol
• Minor style fixes on the same page: Apache Kafka® trademark on first mention, removed "currently" from unsupported features intro, fixed "reach out" phrasing

Test plan

• Local Antora build passes (no new errors or warnings)
• Page renders correctly at /current/develop/kafka-clients/
• KIP-890 bullet renders as a proper list item in both cloud and non-cloud builds

Closes DOC-2012

🤖 Generated with Claude Code

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[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request updates the Kafka clients documentation page with clarifications and additions. Changes include: adding trademark notation to "Apache Kafka®", expanding the compatibility note to include Redpanda and Kafka 4.x clients, reworded guidance for unsupported clients, and a new unsupported Kafka feature entry (KIP-890 Transactions Server-Side Defense) with details about per-transaction epoch bumping behavior. Environment-specific authentication guidance is added for both cloud and non-cloud deployments. Additional notes regarding HTTP Proxy limitations, delete.retention.ms behavior, and client quotas are incorporated with conditional visibility based on environment.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Suggested reviewers

• c4milo
• kbatuigas
• mattschumpert

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	❓ Inconclusive	The description provides a clear summary of changes and includes a test plan with verification steps, but is missing the required template structure (Jira ticket link, page preview, and check categories).	Add the template sections: include the Jira ticket link (DOC-2012), provide page preview URL(s), and select applicable check category (likely Content gap or Support Follow-up).

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically summarizes the main changes: documenting Kafka 4.x client compatibility and KIP-890 support details, with the ticket reference for traceability.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/doc-2012-kafka4x-compatibility

📝 Coding Plan

• Generate coding plan for human review comments

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[coderabbitai]

🧹 Nitpick comments (1)

modules/develop/pages/kafka-clients.adoc (1)

45-45: Consider aligning “unsupported client” with earlier “not validated” terminology.

Line 43 says unvalidated clients can still be compatible, while Line 45 asks users to report an “unsupported client.” “Unvalidated client” would read more consistently.

✏️ Suggested wording tweak

-If you find an unsupported client, contact the Redpanda team in the community https://redpanda.com/slack[Slack^].
+If you find an unvalidated client, contact the Redpanda team in the community https://redpanda.com/slack[Slack^].

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@modules/develop/pages/kafka-clients.adoc` at line 45, Replace the phrase
"unsupported client" with "unvalidated client" in the sentence "If you find an
unsupported client, contact the Redpanda team..." so terminology matches the
earlier "not validated" wording; update the copy that currently uses
"unsupported client" to read "If you find an unvalidated client, contact the
Redpanda team..." to maintain consistency with the phrase used on Line 43.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@modules/develop/pages/kafka-clients.adoc`:
- Line 45: Replace the phrase "unsupported client" with "unvalidated client" in
the sentence "If you find an unsupported client, contact the Redpanda team..."
so terminology matches the earlier "not validated" wording; update the copy that
currently uses "unsupported client" to read "If you find an unvalidated client,
contact the Redpanda team..." to maintain consistency with the phrase used on
Line 43.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: ff2ed267-6e9a-4306-8ce8-b1bc9add75f1

📥 Commits

Reviewing files that changed from the base of the PR and between be11e77 and 061552a.

📒 Files selected for processing (1)

• modules/develop/pages/kafka-clients.adoc

[Feediver1]

Thanks for the quick turnaround @mfernest ! Reminder: be sure to include a preview link to the updated section(s). Thx!