Restore retained activity across reconnects

[VolkerChristian]

Summary

• reconstruct every retained timeline turn and item instead of permanently hiding history beyond the newest 256 items
• preserve existing timeline widgets while authoritative prefix history is restored
• aggregate Agents and collaboration activity across every retained turn instead of only the latest turn
• prevent incomplete structural State publications from deleting retained command or agent rows
• keep linked-agent dependencies and the status-bar activity count stable across partial projections

Root cause

Two independent presentation rules produced the disappearing entries:

1. A structural item upsert could treat omissions from an incomplete State publication as deletion authority.
2. CodexUI always reconstructed only the newest 256 timeline items and only latest-turn Agents. Once history crossed that boundary, reconnecting or restarting deterministically rebuilt the same truncated tail.

The invariant is now consistent: incomplete projections cannot delete retained identities, while complete thread reconstruction materializes all retained history. Agents are thread-history projections rather than latest-turn projections.

Live reproduction

The running CodexUI XVIII thread was captured through UI restart, backend disconnect, and reconnect. Persisted command events remained present, while the old CodexUI binary rebuilt only its truncated activity tail and an empty latest-turn Agents pane. This confirmed presentation loss rather than AISuite persistence loss.

Tests

• complete 40-turn reconstruction in canonical order
• complete 300-item turn reconstruction from earliest through newest item
• append past the former item-257 boundary without head eviction
• retained prefix expansion with keyed QWidget preservation
• bounded incomplete-history proof followed by authoritative recovery
• earlier-turn Agents available on first render after restart
• temporary incomplete agent omission followed by authoritative removal
• structural shell-command omission regression
• full build succeeds
• ctest --test-dir build --output-on-failure -j2: 7/7 passed