Use cases

The project moves in vertical slices. Every use case reaches all the way to Python, and is considered closed when it answers every guarantee on its questionnaire.

How to read it. Each section records a decision at the moment it was taken. The argument is the point — code moved on, the reasoning did not — so what a section says is what was true when it closed, with three exceptions written down once here rather than patched into every section that predates them:

workers={"gpu-box": Worker.at(…)} in Graph.forward and in Trainer became broker=Broker.embedded({…}) in CU28. The shape of what is handed over is the same; what it resolves to is no longer a connection.
the crate called transport moved out to soma-fabric/wire, unchanged, after CU27. Paths in the questionnaires point at where the tests are today.
Transition, Await and Driver — a node that suspends and something that serves what it asked for — were removed after CU18. A node is a function. Sections written before that still show them; After CU18 says why they went.

What each slice settled

		what it settled
CU1	creating a graph	topology only, and errors at insertion rather than in a `validate()`
CU2	executing one	the engine is Rust, `Value` has a closed set of variants
CU3	the shape of it	`Plan` is an enum, and `compile` is the step between structure and engine
CU4	fans both ways	aggregation is a node reading a map; there is no `Aggregator` trait
CU5	the DSL	`>>` and `\|` in both languages, and `somatize` is the verb
CU6 & CU7	one contract	one `Node` with one `forward`, in both languages
CU8	`Opaque`	a value that only exists in this process, asked for by hand
CU9	waves	one thread per branch, decomposed as a tree and not flattened
CU10	the device	`Placement` is a fact of its own; the plan says when, not where
CU11	training	outside the graph, and the three levels the rest rests on
CU12	a worker	`Plan::Remote`, the `Transport` hole, and what does not travel
CU13	the cache	a Merkle key over the recipe, and the `Keeper` hole
CU14	training the far half	a trainer travels and stands beside the node
after	`Opaque` on the wire	a codec in front of it, measured at 9–15×
after	`every=N`	a group of steps is one update
CU15	federated	export is weights node by node, `fedavg` is a function, a round is a `for`
CU16	the grain of an item	an item’s name is its content; micro-batches are level 2
CU17	level 3	`Partition`, `Pruner`, `Sampler` — pure, and no callback crosses
CU18	a study in a folder	a trial is a number, `claim` settles it, the state is the queue
after	a node is a function	`Transition` and `Driver` had no tenant and went
CU19	a graph drawn	observability is three things, and this is the first
after	a bucket	the second `Store`, and `claim` is a conditional PUT
CU20	the record	the `Watcher` hole; facts meet in the record, not in Rust
after	a run drawn	one drawing function, live and read back
CU21	the diagnosis	an opinion about the record, reproducible without training again
CU22	before a step	a probe is one recorded `forward`; what separates is a runaway
after	a block is a box	repeats, lanes, and an arrow that left the drawing
CU23	the fleet	no registry; the record turned the other way up
CU24	the data	a source is a node, and it is handed a coordinate
CU25	not running what nobody needs	names are knowable before anything runs
CU26	what an edit did	two sets of names, and findings rather than buckets
CU27	what a node was built with	the declaration goes in the key
after	the wire leaves	`transport` → `soma-fabric/wire`, and why
CU28	a broker	which broker is a URL; ask eagerly, connect lazily
CU29	provenance	what cannot be recovered is written down when it is known