Feature: Interactive Session Replay with Timeline Scrubber

[hoangsonww]

Problem

Current views show snapshots and event streams, but there is no way to replay a session state over time. This makes debugging long sessions and explaining behavior transitions harder.

Proposal

Add a Session Replay mode that reconstructs session/agent state from persisted events and lets users scrub through time.

Scope

• New Replay page (or panel on Session Detail)
• Timeline scrubber with play/pause/step controls
• Speed controls (0.5x, 1x, 2x, 5x)
• Deterministic reconstruction of agent/session status from events
• Event focus mode (jump to selected event and highlight affected entities)

UX Requirements

• Keyboard shortcuts: space (play/pause), arrows (step)
• Clearly visible current timestamp + event index
• Sticky mini-map of major lifecycle transitions

Technical Notes

• Build a replay state engine from ordered events (created_at, id tie-break)
• Cache computed checkpoints every N events for fast seeking
• Reuse existing status chips/cards for visual consistency

Acceptance Criteria

• User can replay any completed session from start to finish
• Scrubbing to any point updates all visible entities consistently
• Step-forward/back reflects exact next/previous event impact
• Replay can handle sessions with 10k+ events without UI lockups
• Unit tests validate deterministic reconstruction logic