Ensure browser traceId lifetime works as expected

[Lms24]

Problem Statement

In v7, traces in browser SDKs had a bit of a weird lifetime and behavior:

• We created new traces for pageload and navigation transactions as well as for custom (user-created) transactions by default.
• Due to "Tracing w/o Performance" and the introduction of the propagation context, we'd attach traceIds to outgoing requests or non-transaction Sentry events that used a fallback traceId. This traceId would remain valid over the entire host application lifecycle (i.e. until a hard page reload and across browser navigations/URL changes/history changes). This resulted in "orphaned" traces where the fallback trace would potentially collect 100s of events that had nothing to do with each other.

With v8, we're changing the validity and lifetime of a single trace: It'll remain consistent and valid per route. This means:

• on initial pageleoad, we create a new propagation context (i.e. traceId) and keep it valid, even when the pageload root span ended.
• on subsequent browser-based navigations, we update the propagation context and keep it valid, even when the navigation root span ended.
• All events happening within one route (i.e. URL state, browser history state, SPA route, etc) are associated with the trace from the propagation context. This means, the fallback trace from v7 should no longer exist and "orphaned" events/requests should always be associated with the last pageload or navigation trace.

Solution Brainstorm

We already did most of the work in #11377 but identified a lack of tests to cover scenarios. This issue tracks all scenarios we should test as well as potential issues we identify and fix along the way.

Scenarios

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1. multiple subsequent navigations have different traceIds (via feat(tracing-internal): Reset propagation context on navigation #11401)
2. pageload and subsequent navigation have different traceIds (via fix(browser): Ensure pageload trace remains active after pageload span finished #11600)
3. error after pageload has pageload traceId (via fix(browser): Ensure pageload trace remains active after pageload span finished #11600)
4. test(browser-integration-tests): Ensure error after navigation has navigation traceId #11601
   +0
   
5. error during navigation has navigation traceId (test(browser-integration-tests): Test that errors during pageload/navigation have correct trace id #11610)
6. error during pageload has pageload traceId (test(browser-integration-tests): Test that errors during pageload/navigation have correct trace id #11610)
7. outgoing fetch requests have correct traceId (test(browser-integration-tests): Test trace lifetime for outgoing fetch requests #11614)
8. test(browser-integration-tests): Add trace lifetime tests for <meta> tag pageload transactions #11622
   +0
   
9. outgiong xhr requests have correct traceid (test(browser-integration-test): Add trace lifetime tests for XHR requests #11624)
10. test(browser-integration-tests): Add trace lifetime tests in TwP scenario #11636
    +0
    
11. test(browser-integration-tests): Check trace envelope headers in trace lifetime tests #11660
    +0
    
12. [BLOCKED] feedback events have correct traceId (test(browser-integration-test): Add tests to check trace lifetime in user feedback events #11626)

Fixes

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1. fix(browser): Ensure pageload trace remains active after pageload span finished #11600
   +0
   
2. feat(browser): Update propagationContext on spanEnd to keep trace consistent #11631
   +0
   
3. ref(browser): Streamline pageload span creation and scope handling #11679
   +0
   

[Lms24]

Completed