♻️ Rewrite SessionManager with reactive strategy interface

[thomas-lebeau]

Motivation

The existing SessionManager and SessionStore architecture has accumulated complexity through layered abstractions (sessionStore.ts, sessionStoreOperations.ts, product-specific wrappers). This makes it difficult to adopt modern browser APIs like the CookieStore API and Web Locks, and the synchronous mutex-based approach creates contention issues.

This PR rewrites the session management layer with a reactive strategy interface, preparing the foundation for async-first storage (CookieStore API) in v7.

Changes

• Redefine SessionStoreStrategy interface — strategies now own their state and expose it reactively via an observable, replacing the synchronous read/write/mutex pattern
• Rewrite all three storage strategies (cookie, localStorage, memory) to implement the new reactive interface
• Cookie strategy uses Web Locks for cross-tab coordination and cookieObservable for change detection, replacing the polling-based mutex
• Introduce CookieAccess abstraction to decouple cookie read/write from the document.cookie API, preparing for CookieStore API adoption
• Merge SessionStore into SessionManager — remove sessionStoreOperations.ts and consolidate session lifecycle logic; extract strategy selection into sessionStore.ts
• Make SessionManager initialization fully async — startSessionManager accepts an onReady callback, with setSessionState async across all strategies
• Remove product-specific session manager wrappers (rumSessionManager.ts, logsSessionManager.ts) — the generic SessionManager now handles all products
• Extract startTelemetrySessionContext — defer telemetry configuration until the session is ready
• Move cookieObservable from core to rum-core — scoped to where it's actually used
• Adapt rumPublicApi tests to the new async session manager (buffered API calls, clock-based assertions)

Test instructions

yarn test:unit --spec packages/core/src/domain/session/sessionManager.spec.ts
yarn test:unit --spec packages/core/src/domain/session/sessionStore.spec.ts
yarn test:unit --spec packages/core/src/domain/session/storeStrategies/sessionInCookie.spec.ts
yarn test:unit --spec packages/core/src/domain/session/storeStrategies/sessionInLocalStorage.spec.ts
yarn test:unit --spec packages/core/src/domain/session/storeStrategies/sessionInMemory.spec.ts
yarn test:unit --spec packages/rum-core/src/boot/rumPublicApi.spec.ts
yarn test:unit --spec packages/rum-core/src/boot/preStartRum.spec.ts

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

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	170.83 KiB	169.58 KiB	-1.25 KiB	-0.73%	✅
Rum Profiler	6.18 KiB	6.18 KiB	0 B	0.00%	✅
Rum Recorder	27.48 KiB	27.70 KiB	+227 B	+0.81%	✅
Logs	56.45 KiB	54.79 KiB	-1.66 KiB	-2.93%	✅
Rum Slim	128.07 KiB	126.91 KiB	-1.16 KiB	-0.91%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0041	0.0048	+17.07%
RUM - add action	0.0133	0.0182	+36.84%
RUM - add error	0.0135	0.0176	+30.37%
RUM - add timing	0.0026	0.0035	+34.62%
RUM - start view	0.0123	0.0248	+101.63%
RUM - start/stop session replay recording	0.0007	0.0011	+57.14%
Logs - log message	0.0151	0.0257	+70.20%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	26.66 KiB	32.22 KiB	+5.56 KiB
RUM - add action	51.03 KiB	266.51 KiB	+215.48 KiB
RUM - add timing	26.69 KiB	36.77 KiB	+10.08 KiB
RUM - add error	55.05 KiB	280.45 KiB	+225.40 KiB
RUM - start/stop session replay recording	25.75 KiB	35.64 KiB	+9.89 KiB
RUM - start view	461.55 KiB	617.17 KiB	+155.62 KiB
Logs - log message	44.76 KiB	240.59 KiB	+195.83 KiB

🔗 RealWorld

[datadog-prod-us1-4]

⚠️ Tests

✨ Fix all issues with BitsAI or with Cursor

⚠️ Warnings

❄️ 1 New flaky test detected

cookieAccess document.cookie fallback observable (polling) should notify when cookie is changed externally from Safari 12.1.2 (Mac OS 10.14.6)     (Fix with Cursor)

Expected spy observer to have been called only once, and with given args:
  [ 'external' ]
But it was never called.


<Jasmine>
webpack:///packages/core/src/browser/cookieAccess.spec.ts:95:45 <- /tmp/_karma_webpack_131870/commons.js:38117:53
<Jasmine>

ℹ️ Info

No other issues found (see more)

🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 83.63%
• Overall Coverage: 77.67% (+0.33%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: e72f6b8 | Docs | Datadog PR Page | Was this helpful? React with 👍/👎 or give us feedback!}

[chatgpt-codex-connector]

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[BenoitZugmeyer]

nitpick: might be simpler to use mockable (mockable(window.cookieStore) // replaceMockable(window.cookieStore, undefined)

[BenoitZugmeyer]

thought: I think we could have common tests for both implementations. Also, we could use the actual cookie store instead of a mock

const setups = [
  { title: 'document.cookie fallback', setup() { disableCookieStore() } },
  { title: 'cookieStore', setup() { if (!window.cookieStore) pending("No cookie store available") }
]

for (const { title, setup } of setups) {
  describe(title, () => {
    beforeEach(() => setup())

    it('should pas the current values to callback', () => {
      setCookie(...)
  
      const cookieAccess = createCookieAccess(COOKIE_NAME, MOCK_CONFIGURATION, COOKIE_OPTIONS)

      let capturedValues: string[] | undefined
      await cookieAccess.getAllAndSet((values) => {
        capturedValues = values
        return { value: 'new', expireDelay: 1000 }
      })

      expect(capturedValues).toEqual(['value1'])
...

[BenoitZugmeyer]

suggestion: mock the cookieAccess, so you can inject your own "cookieAccess" object, without actually relying on cookies.

const cookieAccess = mockable(createCookieAccess)(SESSION_STORE_KEY, configuration, cookieOptions)

[BenoitZugmeyer]

suggestion: FMU we can't be in expired state here since we are doing "expandOrRenew"

[BenoitZugmeyer]

question: this is quite confusing. Why do we do this?

[BenoitZugmeyer]

suggestion: move previousState = newState in handleStateChange

[BenoitZugmeyer]

suggestion: instead of having a previousState variable, could we use sessionContextHistory.find() to get the latest known session?

[BenoitZugmeyer]

thought: the anonymousId logic is all over the place... maybe we can do something about it

[BenoitZugmeyer]

thought: A sanitized / strongly typed SessionState would help clarify the flow. We shouldn't have to check for various properties to understand the state we're in.

[BenoitZugmeyer]

suggestion: remove sessionStateUpdateObservable as it doesn't seem used anymore