✨ [FFL-2596] Feature Flags tab — overrides (stacked PR 3 of 3)

[kellyw1806]

Motivation

Stacked on #4916 (catalog fetch). Allows users to create overrides for a flag's value (allows for switching between variables) locally and have it take effect on the inspected page.

Stack (review bottom-up)

	PR	Base	What it adds
1 of 3	#4913 · FFL-2597	main	OAuth sign-in
2 of 3	#4916 · FFL-2858	ffl-2597	catalog browsing
3 of 3	#4912 (this) · FFL-2596	ffl-2858	flag overrides

⚠️ Base is kelly.wang/ffl-2858 — merge #4913 then #4916 first.

Changes

• Override engine (useFlagOverrides) writing to the inspected page's localStorage per the DatadogDevtools wrapper contract; mutations serialized to avoid lost updates.
• Per-row variant buttons + revert, a manual override-by-key form, clear-all / save-and-reload.

Demo

This is a recording of what the three stacked PRs look like working together.

Screen.Recording.2026-07-24.at.5.14.31.PM.mov

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change (useFlagOverrides.spec.ts).
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[datadog-prod-us1-5]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 34.48%
• Overall Coverage: 76.95% (-0.22%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 74968df | Docs | Datadog PR Page | Give us feedback!}

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	180.54 KiB	180.54 KiB	0 B	0.00%	✅
Rum Profiler	8.43 KiB	8.43 KiB	0 B	0.00%	✅
Rum Recorder	21.12 KiB	21.12 KiB	0 B	0.00%	✅
Logs	57.05 KiB	57.05 KiB	0 B	0.00%	✅
Rum Salesforce	N/A	138.42 KiB	N/A	N/A	N/A
Rum Slim	138.41 KiB	138.41 KiB	0 B	0.00%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅
Rum Shopify	N/A	200.11 KiB	N/A	N/A	N/A
Rum-shopify Profiler	N/A	8.43 KiB	N/A	N/A	N/A
Rum-shopify Recorder	N/A	3.72 KiB	N/A	N/A	N/A

[kellyw1806]

I have read the CLA Document and I hereby sign the CLA

[kellyw1806]

These keys are a contract with @datadog/openfeature-browser's DatadogDevtools wrapper so renaming them requires a coordinated change in that package, not a free rename.

[kellyw1806]

Widened the override value to allow null (a variant value can legitimately be null). The manual-entry form still rejects null via validateOverrideValue. Is this okay or should variant-click also block null?

[kellyw1806]

This polls the inspected page every 2s while the tab is mounted. Fine for a devtools panel IMO, but flagging in case prefer gating it on tab visibility.