[Juliusolsson05]

Summary

• queue Codex optimistic submits when rendered semantic history still owns the feed tail, preventing submitted prompts from landing above semantic/work rows
• add a Codex-only idle invariant that clears stale local queued prompts once process/stream/awaiting signals are all idle
• add focused regression coverage for semantic-history prompt ownership, committed-owned history, Feed row ordering, and idle queue cleanup

Verification

• npm run test:codex-optimistic-submit
• npm run test:feed-render-model
• npm run test:semantic-committed-text
• npm run test:ghost-fallback
• npm run build

Fixes #239
Addresses #241