fix(firestore): fix fetch connection error message

[dlarocque]

Fixes fetch connection error messages. We now read the thrown error's message and cause instead of attempting to read a potentially non-existent statusText from an Error object, preventing connection failures like ECONNREFUSED from being displayed as undefined.

In tests, we see errors like this

    145) Vectors
         can be read and written using the lite SDK:
       FirebaseError: [code=unknown]: Request failed with error: undefined

Now, they will look like this:

    145) Vectors
         can be read and written using the lite SDK:
       FirebaseError: [code=unknown]: Request failed with error: fetch
  failed (Error: connect ECONNREFUSED 127.0.0.1:8080)

This will also impact users.

Before:

    FirebaseError: [code=unknown]: Request failed with error: undefined

Now:

    FirebaseError: [code=unknown]: Request failed with error: fetch failed
  (ConnectTimeoutError: Connect Timeout Error)

[changeset-bot]

🦋 Changeset detected

Latest commit: 31fb267

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@firebase/firestore	Patch
firebase	Patch
@firebase/firestore-compat	Patch

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[gemini-code-assist]

Code Review

This pull request improves error handling in FetchConnection for the browser-lite platform of Firestore by extracting more detailed error messages (including message and cause) when a fetch request fails. The review feedback points out a potential issue where err.message is undefined but err.cause is present, which would result in a string containing "undefined", and provides a code suggestion to handle this case safely.

[MarkDuckworth]

LGTM with question

[MarkDuckworth]

I don't have enough context on statusText but are there scenarios where either message or cause is defined but statusText still provides useful information, and therefore this change is a regression in surfacing error details?

[dlarocque]

Honestly, I don't think statusText was ever defined on the error object. I think this code was copied from the block above, and response.statusText (valid) was replaced with err.statusText by mistake.

https://github.com/firebase/firebase-js-sdk/pull/3482/changes#diff-91ed949c8a1f344b8e3707a1607fe8e5c89b3b2db8ff4382a67ee52fe118b6d7R65-R76