Replay / Time-Travel

Problem

Agent runs depend on non-deterministic model outputs, accumulated conversation state, and external tool results that may not be the same on the next call. Trying to reproduce a three-day-old bug locally usually fails because too much has changed, and engineers end up debugging by re-running the user's prompt and hoping the model behaves the same way. The team is forced to choose between spending hours on guess-and-check reproduction or shrugging off intermittent bugs that they cannot deterministically trigger.

Solution

Capture per-step inputs, outputs, prompts, model id, tool calls. Provide a replay tool that loads a trace at step N and re-runs forward with optional modifications (different model, different prompt, different tool result). Store branches for comparison.

When to use

• Agent runs are non-deterministic and incidents need reproducible debugging.
• Engineers want to branch from a past step to test fixes or alternative prompts.
• Per-step inputs, outputs, and tool calls can be captured durably.