fix(core): surface abort reasons in errors

[Skn0tt]

This PR keeps the supplied AbortSignal reason in API error messages and call logs. Aborted locator assertions now retain their latest mismatch detail instead of replacing it with an assertion-aborted message.

I ran the same click/expect repros against the merge base and this branch. Only the abort output changes.

locator.click() when aborted:

-AbortError: locator.click: The operation was aborted
+AbortError: locator.click: foo bar
 Call log:
   - waiting for locator('button')
     - locator resolved to <button>click me</button>
   - attempting click action
     2 × waiting for element to be visible, enabled and stable
       - element is not visible
     - retrying click action
     - waiting 20ms
     - waiting for element to be visible, enabled and stable
     - element is not visible
   - retrying click action
     - waiting 100ms
+  - operation was aborted: foo bar

expect(locator) when aborted:

 Error: expect(locator).toBeVisible() failed

 Locator: locator('span')
 Expected: visible
-Error: The assertion was aborted: stop it
+Error: element(s) not found

 Call log:
   - Expect "to.be.visible" with timeout 5000ms
   - waiting for locator('span')
+  - operation was aborted: stop it

I also verified that operation timeouts, test timeouts, and strict-mode violations are unchanged.

Split out of #41751.

[dgozman]

I think this PR would really benefit from before/after error snippets for click/expect that failed due to timeout/abort/strict violation error.

[dgozman]

I think this will also be printed for timeout errors?

[Skn0tt]

no, abort is used exclusively for __abort__ (signals) and for the aborts upon connection closed. Test ended errors go via context.close and abort through scope closure, not through this code path.

[dgozman]

So it seems like cause is more important than error.message itself? Seems strange.

[Skn0tt]

oops that was a remnant, fixed.

[github-actions]

Test results for "tests 1"

5 flaky

⚠️ [chromium-library] › library/video.spec.ts:275 › screencast › should capture navigation `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:645 › screencast › should capture full viewport `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/chromium/chromium.spec.ts:371 › should produce network events, routing, and annotations for Service Worker `@realtime-time-library-chromium-linux`
⚠️ [chromium-library] › library/video.spec.ts:476 › screencast › should capture static page in persistent context @smoke `@chromium-ubuntu-22.04-node24`
⚠️ [chromium-library] › library/beforeunload.spec.ts:130 › should support dismissing the dialog multiple times `@chromium-ubuntu-22.04-node20`

49544 passed, 1168 skipped

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Merge workflow run.

[github-actions]

Test results for "MCP"

1 failed
❌ [msedge] › mcp/cli-core.spec.ts:37 › preserves URL with & query params @mcp-windows-latest-msedge

7759 passed, 1249 skipped

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Merge workflow run.