Writes

The decision: does anything downstream need to react to this edit? The litmus test: if a topology rebuild, a replanner, or a renderer must notice the edit, queue it — dirty metadata only exists on the queued path. When unsure during simulation, queue.

Branches

Branch	Pick when	You commit to
Direct field writes	setup, loading, tests, tools — nothing consumes dirty state	keeping these writes out of the simulation loop
Queued operations	sim-time edits; dirty masks drive topology, replanning, or render deltas; parallel execution may ever matter	declaring a domain, touched fields, dirty mask, and WritePolicy per operation

The declared WritePolicy is what licenses parallel execution later — declare it honestly even while running serial. Completion reporting (result channels) is part of the same contract; the queued-operations note specifies both.

What it looks like

world.field<PassableTag>(tess::Coord3{4, 2, 0}) = 1;

Learn and specify

• Teach: getting-started §4, rung 4; examples/mvp_path.cc is the smallest queued edit, examples/colony_2d.cc the schedule-integrated form.
• Specify: queued-operations note (planning, write policies, result channels).