Windows Desktop freezes on large chats and restored threads disappear from sidebar

Summary

Codex Desktop on Windows becomes practically unusable with long-running large chats, and restored chats may disappear from the sidebar after reinstall even when their session files and index entries are intact.

This is a severe workflow and data-visibility problem for users who keep substantial coding and operations projects in one conversation. Competing desktop assistants remain usable with similarly long histories; Codex should not require users to archive or abandon their main working chat just to type reliably.

Environment

• Windows desktop application
• Store package observed before reinstall: 26.707.9564.0
• Session metadata CLI version: 0.144.2
• Affected active transcript: approximately 260.55 MB / 273,696,359 bytes
• Hot session tree before mitigation: approximately 1.168 GB, 53 files

Symptoms

1. Manual typing freezes the window or produces visible flicker.
2. Voice input from an external dictation application makes the failure easier to trigger, but ordinary typing also freezes.
3. thread/turns/list operations take roughly 2-4 seconds repeatedly.
4. A direct UI-state inspection took approximately 56 seconds and then failed.
5. Renderer logs showed recurring ResizeObserver-related UI errors.
6. Reinstalling the application did not solve the large-chat problem.
7. After restoring a complete backup, several large chats were absent from the normal sidebar even though:

• their .jsonl files were intact;
• their SHA-256 hashes matched the backup;
• their thread IDs and index entries existed;
• direct thread reads worked.

1. The missing threads became discoverable only after manually toggling their archive state / re-registering them.

Large restored sessions involved

• 368,333,366 bytes
• 273,696,359 bytes
• 237,447,022 bytes
• 130,293,463 bytes
• 122,762,931 bytes

Removing these histories from the hot session tree reduced it to about 92 MB and immediately made the application lighter, but hiding or archiving active project history is not an acceptable solution.

Reproduction outline

1. Maintain a long-running Codex Desktop task until its rollout JSONL reaches roughly 250-300 MB.
2. Reopen that task and type several messages, including longer dictated text.
3. Observe increasing input latency, renderer flicker, UI freezes, and slow thread-list calls.
4. Back up %USERPROFILE%\\.codex, reinstall Codex Desktop, and restore the session files and session index.
5. Observe that some large restored threads do not appear in the regular sidebar even though their files and IDs are readable.

Expected behavior

• Message history should be virtualized, paged, or otherwise loaded incrementally.
• Typing and dictation must remain responsive regardless of transcript size.
• Background thread listing must not repeatedly parse entire multi-hundred-megabyte JSONL files.
• Reinstall + restore should deterministically rebuild the thread database/index and display every non-archived chat in the sidebar.
• The application should clearly distinguish archived, quarantined, unindexed, and corrupted sessions instead of silently hiding them.
• A built-in repair/reindex command should be available.

User impact and feedback

The current behavior wasted hours across diagnosis, backup, failed reinstall attempts, recovery, and manual re-registration of chats. The user described the experience as unacceptable and specifically asked that the developers be told that Codex performs dramatically worse than Claude for large-chat workflows and requires constant manual intervention.

Related issue families

This may overlap with reports around large histories/session scanning and Windows renderer instability, including #18693, #20864, #20544, #20269, #22004, and #24904. The missing-sidebar-after-restore behavior may be a separate indexing defect.

Please treat large-chat responsiveness and deterministic restore/reindex behavior as core data-safety and usability requirements, not as an edge-case optimization.