perf: fix ChatListSortRooms redundant rebuilds and lifecycle leaks

[9clg6]

Summary

Fix the chat list sort widget that was re-running an expensive async sort on every frame rebuild, and fix pre-existing lifecycle bugs causing memory leaks.

Problems

1. Redundant sort on every build(): FutureBuilder(future: sortRooms()) was called directly in build(), creating a new Future on every rebuild. Since a parent StreamBuilder triggers rebuilds ~1x/second (rate-limited sync), this launched a full async sort of all rooms every second.

2. Memory leak (pre-existing): No dispose() method — StreamSubscription instances (one per room, listening to room.onUpdate) were never cancelled when the widget was destroyed.

3. Crash risk (pre-existing): sortRooms() accesses context and widget after multiple await calls without checking mounted. If the widget is disposed mid-sort, this throws "Looking up a deactivated widget's ancestor".

4. Concurrent stale futures (pre-existing): Each didUpdateWidget call launched a new sort without invalidating the previous one. Multiple sort futures could run in parallel, mutating shared state and writing to the parent's ValueNotifier.

Solution

• Cache the sort Future in _sortFuture, computed only in initState() and didUpdateWidget() — not in build()
• Add dispose() to cancel all room subscriptions
• Add mounted guards after every await in _sortRooms()
• Add a _sortGeneration counter: each new sort increments it, and in-flight sorts bail out early if their generation is stale

Results

Metrics collected via Chrome DevTools performance trace with CPU 4x throttling (simulating a low-end device). The raw flame chart JSON exceeded 350,000 lines — analysis was automated using the Chrome DevTools MCP on Claude Code to run the app, navigate through conversations, record performance traces, and extract metrics programmatically.

Metric	Before	After	Delta
Long tasks (>50ms) count	33	23	-30%
Long tasks total time	4,145ms	3,521ms	-16.9%
Jank (frames >16.7ms)	90.3%	84.8%	-5.5 pts
JS Heap	79 MB	68 MB	-14%

Files changed

File	Change
lib/pages/chat_list/chat_list_sort_rooms.dart	Fix rebuild + add dispose/mounted/generation

Summary by CodeRabbit

• Bug Fixes

  • Improved chat room list sorting to handle edge cases when widget state changes, ensuring sorting results remain up-to-date and responsive.

• Chores

  • Removed unused import.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 7218792d-f551-4afa-b495-6f0a5c8b2e9e

📥 Commits

Reviewing files that changed from the base of the PR and between 046d017 and 7cb83ee.

📒 Files selected for processing (1)

• lib/pages/chat_list/chat_list_sort_rooms.dart

Walkthrough

This pull request introduces a generation-invalidated sorting pipeline for room list ordering in the chat interface. The sorting logic is refactored to use futures with stale result detection, allowing the system to discard in-flight sort operations when invalidated. Early exit conditions are added to handle widget unmounting and newer sort generation detection. A disposal method cancels subscriptions and increments the generation counter. Additionally, an unused import is removed from a utility file.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title 'perf: fix ChatListSortRooms redundant rebuilds and lifecycle leaks' clearly and specifically describes the main changes: addressing performance issues from redundant rebuilds and fixing lifecycle/memory leak bugs in the ChatListSortRooms widget.
Description check	✅ Passed	The PR description is comprehensive and well-structured. It covers the root causes (redundant rebuilds, memory leaks, crash risk, concurrent futures), the solution (caching, dispose, mounted guards, generation counter), and includes detailed performance metrics demonstrating the impact.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch perf/chat-list-sort-fix

📝 Coding Plan

• Generate coding plan for human review comments

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[github-actions]

This PR has been deployed to https://linagora.github.io/twake-on-matrix/2932

[tddang-linagora]

• Add before after screenshots of the improvement (Either Flutter devtools or Chrome devtools)