engine: a typed parameter schema per command (CommandSpec::form)

Field, Kind, Dim and Collection describe a command's JSON parameters: numbers with
unit dimensions, choices, vectors, references to model items, groups, one-of
variants and rows. prefill, switch_variant and problems serve forms; json_schema
gives the same as JSON Schema. No command is described yet (form: None).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/geometry.rs

@@ -12,6 +12,7 @@ pub const OPEN: CommandSpec = CommandSpec {
     id: "geometry.open",
     label: "Open Design",
     params: r#"{"path": "part.solidcraft"} — rebuilds the SolidCraft design and makes its bodies the geometry; opening it again after an edit picks up the change"#,
+    form: None,
     kind: CommandKind::Model,
     run: open,
 };
@@ -20,6 +21,7 @@ pub const BODIES: CommandSpec = CommandSpec {
     id: "geometry.bodies",
     label: "Bodies",
     params: "{} — the open design's bodies: measures and persistent face names (by face index)",
+    form: None,
     kind: CommandKind::Model,
     run: bodies,
 };
@@ -28,6 +30,7 @@ pub const TESSELLATE: CommandSpec = CommandSpec {
     id: "geometry.tessellate",
     label: "Tessellate Body",
     params: r#"{"body": "Body1", "tolerance": 0.05} — triangulates the body's boundary within the chordal tolerance (mm); reports triangles per face"#,
+    form: None,
     kind: CommandKind::Model,
     run: tessellate,
 };
@@ -36,6 +39,7 @@ pub const IMPORT_MESH: CommandSpec = CommandSpec {
     id: "geometry.import.mesh",
     label: "Import Tagged Mesh",
     params: r#"{"path": "part.3mf"} — adds each build item of a 3MF package as a surface; triangles keep their B-rep face tags (docs/formats/tagged-mesh.md)"#,
+    form: None,
     kind: CommandKind::Model,
     run: import_mesh,
 };