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Recording and Replay

Recording and replay make nondeterministic or unavailable parts of a system repeatable. Boomerang treats recording at two complementary boundaries.

Physical-Boundary Recording

Physical-boundary recording captures inputs from outside the deterministic reactor graph: sensors, clocks, operators, hardware interrupts, and external systems. Physical actions are the intended entry point for these inputs.

A recording preserves each value and its complete logical tag. Replaying those inputs into the same graph should reproduce the same observable logical trace, subject to the documented runtime and platform assumptions.

Deployment-Boundary Recording

Deployment-boundary recording captures messages crossing an enclave or federate interface. It allows CI to replace a partition—such as a sensor ECU or planning subsystem—with trace-backed endpoints while the rest of the graph runs live.

For a one-way producer, replay injects the recorded outbound messages at their original tags. For a bidirectional or feedback interface, a useful recording contains both directions: replay supplies the replaced partition’s outputs and validates that the live system produces inputs compatible with the recorded interaction. A static recording cannot respond correctly to novel inputs; that requires a behavioral model rather than replay.

Recording Contract

Portable recordings should use stable logical identities rather than runtime allocation keys. A boundary event needs at least:

  • the stable endpoint or action identity;
  • direction and payload schema;
  • the full logical tag, including microstep; and
  • deterministic ordering information for events sharing a tag.

Recordings may also carry a graph or interface fingerprint so incompatible graphs fail clearly instead of producing misleading results.

Current Status

Boomerang currently has action recording/replay foundations backed by MCAP. Stable deployment-independent identities, full boundary recording, partition substitution, and deployment-equivalence trace comparison are architectural goals and are not yet complete. In particular, deterministic replay must preserve microsteps and must not depend on enclave or action keys that can change when a graph is repartitioned.