The proposer half of Collapse: an arrangement an author built by hand, read back as the StatifierBlocks.Composite.Data declaration that stands for it (ADR-0005 part (iii), amended 2026-09-07, clauses 15E to 20E).

propose/3 reads; it writes nothing. It takes no socket, no assigns and no StatifierBlocks.Edit.Session, it is callable from a test, a script or a host's own code with no LiveView in the picture, and it is the only entry point this package offers to Collapse's first half.

{:ok, declaration} = Collapse.propose(document, palette, ["blk_7", "blk_9"])

What comes back is the storable row, minus its name

The {:ok, ...} value is JSON-shaped, in the shape StatifierBlocks.Composite.Data.declaration/1 accepts, with "version", "params", "subtree" and - where the selection holds an unfilled slot - "slots". It carries no "type_name" (15E): a type name is a key in the host's palette namespace, the host is the only party that knows what is registered there, and a package that minted one would be minting a collision it cannot see. So declaration/1 refuses the row until the host names it, and that refusal is the seam working rather than a gap in it.

"sentence" and "palette_entry" are omitted for the same reason at one remove: both are prose or presentation the author never typed in this gesture, and a proposer that invented an English sentence or an icon would be inventing content and calling it a proposal.

Which values become params

18E. The proposed params are the config values the author marks in the gesture; where the author marks none, every value that differs from its field's declared default. A value left at its default is a value the author never chose, and a param whose default is the field's default parameterises nothing.

The marks are the gesture's, so they arrive beside the three arguments 15E fixes rather than inside them: propose/4's option list carries marks: %{block_id => [field key]}, and propose/3 - the record's entry point, and the whole of what a caller with no gesture behind it needs - is the unmarked reading. Neither of the three arguments is a name, which is the property RQ-SF038-1 fixes the arity for.

Each param's field declaration is the source field's: its "type", "label" and whichever of "required?", "value_path", "datamodel_path?", "hidden?" and "readonly?" the source field declares, carried across unchanged, with "default" set to the value the block's config held. Nothing is re-derived, so the control the author sees on the composite's form is the control they were looking at on the block.

A param's key is the source field's key. Where two blocks in one arrangement declare the same field key - two core.assigns both declare path - every colliding param takes <id_suffix>_<field key> instead and the un-colliding ones keep their bare keys.

The template, and the ids it mints

The template is the subtree with each proposed value replaced by %{"$param" => key} and every other config value carried across as the literal it is. A value that genuinely is a one-key "$param" (or "$literal") map is carried as %{"$literal" => ...}, which is what that escape exists for.

"id_suffix" is minted from the source block's type, not from its id: the type name's last dot-separated segment - core.invoke gives invoke, core.assign gives assign - with a positional discriminator appended where a type repeats, in document order: assign, assign_2, assign_3. A document id is arbitrary (blk_7), carries no meaning to a later reader, and need not match the "id_suffix" pattern, while a type segment does.

One consequence, stated because it is sharp: a use-composite twin of a collapsed declaration expands byte-identically only if its authored id_suffixes are the ones this rule mints. ADR-0002's "Guarded step" is authored with call and guard, so its expansion's ids are blk_GS_call and blk_GS_guard where a collapse of the same arrangement mints blk_GS_invoke and blk_GS_assign. The configs, the types and the tree shape are identical; the ids are not, and the rule cannot ask an author who is not there.

Slots

20E. Exactly one subtree under one parent (12E, unamended): two siblings, a block and a cousin, or a partial subtree with a child left outside are refused. A selection whose subtree holds an unfilled slot is admitted, and that slot is proposed as a pass-through slot - "slots" => %{name => [local_id, inner_slot]} - in the shape ADR-0002's pass-through amendment fixes. A filled slot is not proposed and its children are not lifted: they are part of what the author selected, and a Collapse that silently turned them into an opening would be deciding for the author that the blocks they put there were an example rather than the thing.

The replacement is a separate function the host calls, or does not

17E. replacement/4 answers the {:compound, ...} that puts the composite where the arrangement was. Nothing in this package calls it: the gesture does not, and on_collapse does not. A host that saves a declaration and never swaps the arrangement out has done a legitimate thing, and the swap can only happen after the host has stored the declaration, named it and rebuilt its palette with it - until then the :insert names a type the document cannot resolve.

The composite it inserts takes the collapsed root's own id. An expansion mints member ids as composite_id <> "_" <> local_id, so the id given here is the prefix of every state id the chart grows where the arrangement was, and a minted one would put a fresh UXID there on every commit.