Debug log: harnesses fail like Heisenbugs

The expectation is that a harness isolates agent state, so failures are 100% reproducible.

In production, context leakage, ephemeral file handles and ambient tool state cause non-deterministic failures.

The fix is to treat each harness as the OS, with immutable snapshot boots, explicit tool scoping, replayable timelines and reasoning-level early warning.

The harness isolates the environment, and monitoring catches semantic displacement.

Immutable snapshot boots start every agent from a clean, frozen state with no residue.

Explicit tool scoping removes ambient access. If a tool isn't in the MCP definition, it doesn't exist.

Replayable timelines rehydrate the exact state to debug a failure, instead of chasing a static log.

Reasoning-level early warning monitors semantic displacement between steps, as described in the ProMAS paper, and catches failures before the cascade.

Hermeticity (Bazel docs)

Model Context Protocol

ProMAS paper (arXiv 2603.20260)