[codex] Fix conversation history restore decoding

[jskoiz]

What changed

• fixed ConversationStore's async history index loader to decode ISO-8601 dates before reading persisted metadata
• fixed ConversationSnapshotLoader to use the same ISO-8601 date decoding when restoring saved conversations

Why

Persisted conversation files and the history index are written with ISO-8601 timestamps. The async restore path was using a plain JSONDecoder, so restores could fail after the app had already saved valid history.

User impact

• saved chats restore correctly after relaunch or reinstall
• the app stops falling back to fresh empty conversations when existing history is present
• chat history and archive counts stay aligned with the actual saved threads instead of drifting from failed restores

Root cause

ConversationStore encoded dates as ISO-8601 but two async decode paths did not set dateDecodingStrategy = .iso8601. That mismatch broke history restoration and pushed the app into creating replacement empty threads.

Validation

• built the PR branch for iOS Simulator with scheme Yemma4
• manually reproduced the history flow in the simulator before the fix and confirmed the clean branch compiles with the restore patch applied

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
yemma-4	Ready	Preview, Comment	Apr 15, 2026 11:58pm

[jskoiz]

@codex review please run a code review on the latest PR head.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[jskoiz]

Codex review pass: I did not find a blocking issue in this pass. Caveat: I did not run local tests; this is the narrow ISO-8601 restore fix, but PR checks only show GitGuardian/Vercel-style checks, not an iOS build/test lane.

[jskoiz]

Closing during open-PR cleanup: superseded by #36, which carries the async restore decoding fix with targeted tests. No code was merged from this branch.