feat: Flutter SDK update for version 23.2.0

[ArnabChatterjee20k]

This PR contains updates to the Flutter SDK for version 23.2.0.

[greptile-apps]

Greptile Summary

This PR bumps the Flutter SDK to version 23.2.0 and refactors the realtime subscription protocol from URL-encoded query parameters to WebSocket messages via a new _sendSubscribeMessage() method. Version headers, pubspec.yaml, and the README dependency pin are all updated consistently.

Two concerns flagged in prior review rounds remain unaddressed in lib/src/realtime_mixin.dart: the slot+1 collision in the connected handler that can silence events for one of two concurrent subscriptions on reconnect, and the _pendingSubscribeSlots list being cleared and rebuilt on every _sendSubscribeMessage() call which can mis-route responses when multiple subscribe messages are in-flight. The unused import '../models.dart' as models; in service.dart also remains.

Confidence Score: 4/5

Safe to merge for single-subscription use cases; multi-subscription reconnect correctness bugs from prior review remain open.

Two P1 findings from previous review rounds (connected-handler slot collision, _pendingSubscribeSlots race) are still present and unaddressed. No new critical issues found beyond a P2 README vagueness nit.

lib/src/realtime_mixin.dart — connected-handler slot+1 collision and _pendingSubscribeSlots race condition remain unresolved.

Important Files Changed

Filename	Overview
lib/src/realtime_mixin.dart	Major refactor: subscriptions are now sent via WebSocket messages instead of URL query params; introduces _sendSubscribeMessage() and _pendingSubscribeSlots, but the connected-handler slot+1 collision and _pendingSubscribeSlots race (flagged in prior review) remain unresolved.
lib/src/service.dart	Adds unused import '../models.dart' as models; — will trigger a Dart unused_import lint warning (flagged in prior review).
README.md	Version dependency updated to ^23.2.0; compatibility note changed from specific '1.9.x' to vague 'latest'.
lib/src/client_browser.dart	Routine version bump of x-sdk-version header from 23.1.0 to 23.2.0.
lib/src/client_io.dart	Routine version bump of x-sdk-version header from 23.1.0 to 23.2.0.
pubspec.yaml	Package version bumped from 23.1.0 to 23.2.0 — matches SDK headers and README.
CHANGELOG.md	Added 23.2.0 changelog entry describing SDK regeneration and README update.
test/services/account_test.dart	Added isA<models.Session> and isA<models.Token> type assertions to OAuth2 tests — improves test coverage for return types.

_{Reviews (3): Last reviewed commit: "Commit from GitHub Actions (Format and p..." | Re-trigger Greptile}

[greptile-apps]

Unused import

models is imported but never referenced anywhere in the Service class body. This will trigger a Dart unused_import lint warning.

Suggested change

	import '../models.dart' as models;
	import 'client.dart';

[greptile-apps]

_pendingSubscribeSlots race between multiple in-flight subscribe messages

_pendingSubscribeSlots is cleared and rebuilt every time _sendSubscribeMessage is called. Because responses arrive in order but the list is mutated before earlier responses land, a slot can be mapped to the wrong subscriptionId.

Concrete scenario:

1. Subscribe slot A → _sendSubscribeMessage → _pendingSubscribeSlots = [A]
2. Subscribe slot D arrives while (1) is in-flight → _sendSubscribeMessage → _pendingSubscribeSlots = [A, D]
3. Slot A is closed → _sendSubscribeMessage → _pendingSubscribeSlots = [D]
4. Response to (1) arrives: subscriptions[0].subscriptionId = "s_A" — but _pendingSubscribeSlots[0] is now D, so _slotToSubscriptionId[D] = "s_A". Events for channel A will be incorrectly dispatched to slot D's callback until the response to (3) overwrites the entry.

Consider versioning each batch (e.g., a monotonic sequence tag included in the subscribe message and echoed in the response), so stale responses can be discarded.

[greptile-apps]

Slot+1 shifting collides on multi-subscription reconnect

When the server sends a 0-based connected subscriptions map and there are ≥2 client subscriptions (client slots start at 1), both server slot N and server slot N+1 resolve to the same client slot N+1, overwriting the first mapping and leaving the higher-indexed slot with no subscriptionId.

Concrete example — client has slots 1 and 2, server returns {"0":"s_a","1":"s_b"}:

• Server "0" → direct slot 0 missing → shifted slot 1 found → _slotToSubscriptionId[1] = "s_a"
• Server "1" → direct slot 1 found → _slotToSubscriptionId[1] = "s_b" (overwrites "s_a")
• Result: slot 2 has no subscriptionId; all events for that subscription are silently dropped.

Consider using _pendingSubscribeSlots (populated by _sendSubscribeMessage) as the authoritative index → slot mapping for connected payloads too, the same way the response case does at lines 148–161.