fix(solidstart): Read server action route from the request's root span (#25513)

This fixes the `E2E solidstart-2` failure on `develop`. Since #25295,
the "sends a server action span on client navigation" test times out
because the `POST getPrefecture` segment is never sent.

_Root cause:_ After #25295, Nitro's h3 route handler opens a `handler`
span instead of a nested `http.server` span.
`withServerActionInstrumentation` decided whether to rename the segment
by reading the attributes of the *active* span. Now that span is the
`handler` span, which has no `url.path`, so the `/_server` check never
matched and the server action name was never applied.

The fix reads the attributes from the root span instead. That is the
request's `http.server` span, the one `setHttpServerSpanRouteAttribute`
renames, so the check and the rename now target the same span whatever
the framework nests in between.

Locally, `solidstart-2` E2E fails 1/9 (this test) without the change and
passes 9/9 with it.

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via **Francesco Gringl-Novy**.
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Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>
Co-authored-by: Francesco Gringl-Novy <francesco.novy@sentry.io>

Author: sentry-junior[bot]

packages/solidstart/src/server/withServerActionInstrumentation.ts

@@ -1,6 +1,6 @@
 import { handleCallbackErrors, SPAN_STATUS_ERROR } from '@sentry/core';
 import { flushIfServerless } from '@sentry/core/server';
-import { captureException, getActiveSpan, spanToJSON, startSpan } from '@sentry/node';
+import { captureException, getActiveSpan, getRootSpan, spanToJSON, startSpan } from '@sentry/node';
 import { isRedirect } from './utils';
 import {
   SENTRY_SEGMENT_NAME_SOURCE,
@@ -25,7 +25,9 @@ export async function withServerActionInstrumentation<A extends (...args: unknow
   const activeSpan = getActiveSpan();
 
   if (activeSpan) {
-    const spanData = spanToJSON(activeSpan).attributes;
+    // Read the request's `http.server` root span, which is the span we rename. The active span is
+    // usually a framework handler span (e.g. Nitro's h3 `handler` span) without any URL attributes.
+    const spanData = spanToJSON(getRootSpan(activeSpan)).attributes;
 
     // In solid start, server function calls are made to `/_server` which doesn't tell us
     // a lot. We rewrite the span's route to be that of the sever action name but only

packages/solidstart/test/server/withServerActionInstrumentation.test.ts

@@ -169,6 +169,28 @@ describe('withServerActionInstrumentation', () => {
     expect(mockSpanSetAttribute).to.toHaveBeenCalledWith(SENTRY_SEGMENT_NAME_SOURCE, 'route');
   });
 
+  it('sets a server action name on the root span when the active span is a nested handler span', async () => {
+    const rootSpan = new SentryCore.SentrySpan({
+      attributes: {
+        'url.path': '/_server',
+        [SENTRY_OP]: 'http.server',
+      },
+    });
+    const handlerSpan = new SentryCore.SentrySpan({
+      attributes: {
+        [SENTRY_OP]: 'handler',
+      },
+    });
+    SentryCore.addChildSpanToSpan(rootSpan, handlerSpan);
+    mockGetActiveSpan.mockReturnValue(handlerSpan);
+    const mockRootSpanSetAttribute = vi.spyOn(rootSpan, 'setAttribute');
+
+    await serverActionGetPrefecture();
+
+    expect(mockRootSpanSetAttribute).toHaveBeenCalledWith('http.route', 'getPrefecture');
+    expect(mockRootSpanSetAttribute).toHaveBeenCalledWith(SENTRY_SEGMENT_NAME_SOURCE, 'route');
+  });
+
   it('does not set a server action name if the active span had a non `/_server` `url.path`', async () => {
     const span = new SentryCore.SentrySpan();
     span.setAttribute('url.path', '/users/5');