♻️ Simplify session manager architecture

[thomas-lebeau]

Motivation

The session manager has accumulated complexity over time that makes it harder to maintain and debug. This PR simplifies the architecture by:

1. Replacing polling with event-driven sync - Instead of polling every second to detect cross-tab session changes, we now use CookieStore API and localStorage storage events for instant notification
2. Replacing custom lock mechanism with Web Locks API - The complex cookie-based lock with 100 retries has been replaced with the native Web Locks API
3. Removing SessionContext layer - Products now work directly with SessionState instead of going through an intermediate SessionContext transformation

Changes

Architecture Changes

flowchart TB
    subgraph Before["Before"]
        direction TB
        SS1[SessionState] --> |"buildSessionContext()"| SC1[SessionContext]
        SC1 --> |"findSession()"| RSM1[RumSession]
        Poll1[("⏱️ 1s polling")] --> |"watchSession()"| SS1
        Lock1[("🔒 Cookie lock\n100 retries × 10ms")] --> SS1
    end
    
    subgraph After["After"]
        direction TB
        SS2[SessionState] --> |"findSessionState()"| RSM2[RumSession]
        Events[("📡 Storage events\nCookieStore / localStorage")] --> |"instant sync"| SS2
        Lock2[("🔒 Web Locks API\nnative mutex")] --> SS2
    end

Loading

Key Changes

Component	Before	After
Cross-tab sync	1s polling interval	Event-driven (CookieStore API, storage events) + fallback polling
Locking	Cookie-based lock with retries (~136 lines)	Web Locks API (~73 lines)
Session access	SessionState → SessionContext<T> → RumSession	SessionState → RumSession
Type safety	Generic SessionManager<TrackingType>	Non-generic SessionManager

Files Modified

Core package:

• storageObservable.ts - New file with cookie and localStorage observables (moved from rum-core)
• sessionStore.ts - Added event-driven sync subscriptions
• sessionStoreOperations.ts - Replaced custom lock with Web Locks API
• sessionManager.ts - Removed SessionContext, simplified to expose SessionState directly

RUM/Logs packages:

• rumSessionManager.ts - Updated to work directly with SessionState
• logsSessionManager.ts - Updated to work directly with SessionState

Test instructions

1. Run unit tests: yarn test:unit
2. Run e2e tests: yarn test:e2e
3. Manual testing:
   • Open app in 2+ tabs
   • Verify session sync when activity in one tab
   • Verify stopSession() propagates to all tabs
   • Test consent grant/revoke across tabs

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	168.27 KiB	167.83 KiB	-443 B	-0.26%	✅
Rum Profiler	4.32 KiB	4.33 KiB	+1 B	+0.02%	✅
Rum Recorder	24.54 KiB	24.54 KiB	+1 B	+0.00%	✅
Logs	56.47 KiB	56.51 KiB	+41 B	+0.07%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	125.15 KiB	124.75 KiB	-410 B	-0.32%	✅
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	0.0043	0.0064	+48.84%
RUM - add action	0.0139	0.0203	+46.04%
RUM - add error	0.0128	0.0166	+29.69%
RUM - add timing	0.0031	0.0041	+32.26%
RUM - start view	0.0033	0.0054	+63.64%
RUM - start/stop session replay recording	0.0007	0.001	+42.86%
Logs - log message	0.016	0.0238	+48.75%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	28.80 KiB	33.26 KiB	+4.47 KiB
RUM - add action	54.75 KiB	227.74 KiB	+172.99 KiB
RUM - add timing	27.90 KiB	28.64 KiB	+756 B
RUM - add error	58.70 KiB	220.79 KiB	+162.10 KiB
RUM - start/stop session replay recording	26.69 KiB	39.86 KiB	+13.17 KiB
RUM - start view	429.60 KiB	539.55 KiB	+109.95 KiB
Logs - log message	49.86 KiB	220.28 KiB	+170.42 KiB

🔗 RealWorld

[datadog-datadog-prod-us1]

⚠️ Tests

✨ Fix all issues with Cursor

⚠️ Warnings

🧪 29 Tests failed

logs entry post start API usages account should call clearContext from Chrome Headless 139.0.0.0 (Linux 0.0.0) (Datadog) (Fix with Cursor)

Error: Expected spy clearContext to have been called once. It was called 0 times.
    at <Jasmine>
    at UserContext.<anonymous> (/go/src/github.com/DataDog/browser-sdk/packages/logs/src/boot/logsPublicApi.spec.ts:240:45 <- /tmp/_karma_webpack_882784/commons.js:160241:53)
    at <Jasmine>

logs entry post start API usages account should call removeContextProperty from Chrome Headless 139.0.0.0 (Linux 0.0.0) (Datadog) (Fix with Cursor)

Error: Expected spy removeContextProperty to have been called once. It was called 0 times.
    at <Jasmine>
    at UserContext.<anonymous> (/go/src/github.com/DataDog/browser-sdk/packages/logs/src/boot/logsPublicApi.spec.ts:234:54 <- /tmp/_karma_webpack_882784/commons.js:160236:62)
    at <Jasmine>

logs entry post start API usages account should call setContext from Chrome Headless 139.0.0.0 (Linux 0.0.0) (Datadog) (Fix with Cursor)

Error: Expected spy setContext to have been called once. It was called 0 times.
    at <Jasmine>
    at UserContext.<anonymous> (/go/src/github.com/DataDog/browser-sdk/packages/logs/src/boot/logsPublicApi.spec.ts:222:43 <- /tmp/_karma_webpack_882784/commons.js:160226:51)
    at <Jasmine>

View all

ℹ️ Info

❄️ No new flaky tests detected

🎯 Code Coverage
• Patch Coverage: 82.14%
• Overall Coverage: 77.32% (+0.05%)

View detailed report

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