[cloud_firestore_web] Regression in 6.10.0: Document snapshot streams stall on Web after authentication state transition

### Is there an existing issue for this?

- [x] I have searched the existing issues.

### Which plugins are affected?

Cloud Functions, Database

### Which platforms are affected?

Web

### Description

### Description
Following the update from `cloud_firestore: 6.9.0` (`firebase_core_web: 3.11.0`) to `cloud_firestore: 6.10.0` (`firebase_core_web: 3.12.0`), Firestore document snapshot streams (`doc(...).snapshots()`) fail to emit data or deliver snapshot events on **Flutter Web**.

Native platforms (macOS / iOS / Android) are unaffected and continue to work as expected. 

Pinning `cloud_firestore: 6.9.0` (and `firebase_core_web: 3.11.0`) immediately resolves the issue without any changes to application code.

### Reproducing the issue

1. Configure a Flutter Web application with `cloud_firestore: 6.10.0` and `firebase_auth: 6.7.0` (or `firebase_core_web: 3.12.0`).
2. Authenticate a user via Firebase Auth (e.g., custom token or standard provider).
3. Listen to a document snapshot stream:
   ```dart
   FirebaseFirestore.instance
       .collection('users')
       .doc(userId)
       .snapshots()
       .listen((snapshot) {
         print('Received snapshot: ${snapshot.data()}');
       });
4. Observe network activity in Chrome DevTools:
- WebChannel establishes an initial handshake (`Listen/channel`).
- Following the auth state transition, the unauthenticated WebChannel session is terminated (`TYPE=terminate` / aborted GET long-poll with `Unknown SID`).
- The subsequent snapshot listener on the authenticated session never emits events to the Dart stream listener; the stream hangs indefinitely with no error or data emitted.

### Expected Behavior

`snapshots()` should emit document snapshots when listening to accessible documents on Flutter Web, matching the behavior in `cloud_firestore: 6.9.0`.

---

### Actual Behavior

The stream hangs and never emits the initial document snapshot or subsequent updates. No error is thrown through `.handleError()`.


### Firebase Core version

4.15.0

### Flutter Version

3.47.2

### Relevant Log Output

```shell
// 1. Initial WebChannel Listen handshake and subscription registration (Pre-Auth / Transition)
webchannel_connection.ts:317 Fetch finished loading: POST "https://firestore.googleapis.com/google.firestore.v1.Firestore/Listen/channel?VER=8&database=projects%2F<PROJECT_ID>%2Fdatabases%2F(default)&RID=36868&CVER=22&X-HTTP-Session-Id=gsessionid&zx=o6xdvuy44xqx&t=1"
    (anonymous) @ stream_controller.dart:618
    (anonymous) @ js_allow_interop_patch.dart:367
    __PRIVATE_onWatchStreamOpen @ remote_store.ts:572
    (anonymous) @ persistent_stream.ts:532
    then @ async_queue_impl.ts:137

// 2. Target added to listen to document snapshot
webchannel_connection.ts:333 Fetch finished loading: POST "https://firestore.googleapis.com/google.firestore.v1.Firestore/Listen/channel?VER=8&database=projects%2F<PROJECT_ID>%2Fdatabases%2F(default)&gsessionid=<GSESSION_ID>&SID=Xe1mhnSSZdjYxYx5OqJXQw&RID=36869&AID=1&zx=6iucu6uk4c7m&t=1"
    (anonymous) @ stream_controller.dart:618
    (anonymous) @ js_allow_interop_patch.dart:367
    asyncQueue @ firestore_client.ts:528

// 3. User authenticates via Firebase Auth. Unlisten / session teardown triggered:
__PRIVATE_syncEngineImpl @ sync_engine_impl.ts:482
__PRIVATE_eventManagerUnlisten @ event_manager.ts:271
fromCache @ firestore_client.ts:795
then @ async_queue_impl.ts:137

// 4. In-flight WebChannel long-poll GET is terminated / aborted:
webchannel_connection.ts:317 Fetch failed loading: GET "https://firestore.googleapis.com/google.firestore.v1.Firestore/Listen/channel?gsessionid=<GSESSION_ID>&VER=8&database=projects%2F<PROJECT_ID>%2Fdatabases%2F(default)&RID=rpc&SID=Xe1mhnSSZdjYxYx5OqJXQw&AID=0&CI=0&TYPE=xmlhttp&zx=x6izydofjgit&t=1"
    (anonymous) @ webchannel_blob_es2018.js:49
    (anonymous) @ webchannel_blob_es2018.js:57
    Eb @ webchannel_blob_es2018.js:25

// 5. Querying the terminated SID endpoint returns 400 Bad Request:
// HTTP/2 400 Bad Request
// <!DOCTYPE html>
// <html lang=en><title>Error 400 (Bad Request)!!1</title>
// <p><b>400.</b> <ins>That’s an error.</ins>
// <p>Your client has issued a malformed or illegal request. Unknown SID <ins>That’s all we know.</ins>

// 6. Result:
// The authenticated snapshot stream listener fails to deliver events to the Dart StreamSubscription.
// Document exists and is readable via authenticated REST API, but Stream<DocumentSnapshot> hangs indefinitely.
```

### Flutter dependencies

- __Failing Versions__:

  - `cloud_firestore: 6.10.0`
  - `cloud_firestore_web: 5.7.4` (or transitive `5.7.3` with `firebase_core_web: 3.12.0`)
  - `firebase_core_web: 3.12.0` (bundled Firebase JS SDK `12.19.0`)

- __Working Versions__:

  - `cloud_firestore: 6.9.0`
  - `cloud_firestore_web: 5.7.3`
  - `firebase_core_web: 3.11.0` (bundled Firebase JS SDK `12.18.0`)



### Additional context and comments

- In Chrome DevTools Network panel, the previous WebChannel long-polling channel aborts when authentication completes, and any subsequent poll to the terminated session ID returns `400 Bad Request (Unknown SID)`.

- Verified via authenticated Firestore REST API (`GET https://firestore.googleapis.com/v1/projects/<PROJECT>/databases/(default)/documents/...`) that the target document exists and security rules permit read access with the active auth token.

- Reverting solely the FlutterFire dependencies back to `cloud_firestore: 6.9.0` and `firebase_core_web: 3.11.0` (Firebase JS SDK `12.18.0`) restores stream emissions immediately.


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[cloud_firestore_web] Regression in 6.10.0: Document snapshot streams stall on Web after authentication state transition #18700

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[cloud_firestore_web] Regression in 6.10.0: Document snapshot streams stall on Web after authentication state transition #18700

Description

Is there an existing issue for this?

Which plugins are affected?

Which platforms are affected?

Description

Description

Reproducing the issue

Expected Behavior

Actual Behavior

Firebase Core version

Flutter Version

Relevant Log Output

Flutter dependencies

Additional context and comments

Activity

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

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