feat: implement remote configuration caching mechanism

[gogusarov]

Motivation

Support remote configuration caching mechanism according to the RFC

Changes

The remote configuration is no longer awaited during DD_RUM.init it is now read synchronously from a versioned localStorage cache (dd_rc_<remoteConfigurationId>) and applied on the same page load. A background fetch always runs in parallel and refreshes the cache for the next page load, so updates roll out one load late but startup is unblocked. Cache outcomes (hit/miss/error) and fetch outcomes (success/failure) are reported via the existing telemetry metrics. Unit tests cover the new cache module and the read/apply/fetch flow; the e2e scenarios were rewritten to wait for the cache to be populated and reload the page before asserting.

Test instructions

1. add remote-config.json file to sandbox directory
2. update parameters, passed to DD_RUM.init adding remoteConfigurationId: 'remote-config-test', remoteConfigurationProxy: '/remote-config.json'
3. check that remote config from file is requested and written to localStorage on the first page load (localStorage.getItem('dd_rc_remote-config-test')
4. check that DD_RUM.getInitConfiguration() returns initial configuration on the first page load
5. check that DD_RUM.getInitConfiguration() returns remote configuration on the second page load

Checklist

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

[datadog-prod-us1-6]

✨ Fix all issues with BitsAI or with Cursor

⚠️ Warnings

🧪 1 Test failed

cookieAccess CookieStore API observable should notify when cookie is deleted externally from Chrome 145.0.0.0 (Android 10)     (Fix with Cursor)

Error: Timeout - Async function did not complete within 5000ms (set by jasmine.DEFAULT_TIMEOUT_INTERVAL)
    at <Jasmine>

ℹ️ Info

No other issues found (see more)

❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 84.09%
• Overall Coverage: 76.98% (+0.03%)

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[gogusarov]

@mormubis would it be ok to leave metrics keys the way they currently are (success / missing / failure) or should they be exactly the same as in your RFC (hit/miss/error)

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	169.51 KiB	170.35 KiB	+857 B	+0.49%	✅
Rum Profiler	5.97 KiB	5.97 KiB	-1 B	-0.02%	✅
Rum Recorder	21.23 KiB	21.23 KiB	-1 B	-0.00%	✅
Logs	54.70 KiB	54.70 KiB	0 B	0.00%	✅
Rum Slim	127.85 KiB	128.67 KiB	+841 B	+0.64%	✅
Worker	22.99 KiB	22.99 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0031	0.0031	0.00%
RUM - add action	0.0164	0.0143	-12.80%
RUM - add error	0.0137	0.0138	+0.73%
RUM - add timing	0.0007	0.0007	0.00%
RUM - start view	0.0151	0.0121	-19.87%
RUM - start/stop session replay recording	0.0013	0.0009	-30.77%
Logs - log message	0.0234	0.021	-10.26%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	38.75 KiB	37.96 KiB	-811 B
RUM - add action	64.74 KiB	69.80 KiB	+5.07 KiB
RUM - add timing	36.82 KiB	37.28 KiB	+464 B
RUM - add error	70.81 KiB	79.83 KiB	+9.02 KiB
RUM - start/stop session replay recording	41.37 KiB	50.83 KiB	+9.46 KiB
RUM - start view	486.34 KiB	477.06 KiB	-9.28 KiB
Logs - log message	55.35 KiB	65.82 KiB	+10.48 KiB

🔗 RealWorld

[gogusarov]

I updated these tests using withHead so that they pass, but there’s an issue here that we should definitely address later

Remote Configuration currently supports dynamic options, one of which is dom. If we use synchronous bundle setup and Remote Configuration is loaded from the cache immediately, this strategy will always fail because SDK initialization happens before the DOM is available

[thomas-lebeau]

That's a good point, but it might break existing customer setup if we don't address this now, no?

We can change the test, but we can't change our customer setup

[gogusarov]

It seems like it's not something we should solve immediately because currently remote config is only available for SSI clients and from what I know they have hardcoded v6 version and they can't update on their own until we update the injector

[thomas-lebeau]

💬 suggestion: I think with your change, all the test are now relying on the config being cached and we don't test that the remote config works properly even without cache.

I would rather keep waitForRemoteConfigurationToBeApplied as before and add a separate test specifically for the caching mechanism.