IR data model

Source: docs/10-dry-ir-v0-spec.md

3. Data model

3.1 Toolpath

Field	Type	Notes
version	u32	IR schema version. v0 ⇒ 0. Always present on the JSON wire (even when 0).
meta	Meta | absent	Optional self-describing header (§3.2). Omitted entirely when absent.
segments	array of Segment	Ordered move stream. MAY be empty.

3.2 Meta

Optional provenance + declared invariants. Every field is omitted when empty, so a header-free toolpath has no meta key at all.

Field	Type	Notes
generator	string	Producing tool + version, e.g. "dry 0.2.0". Omitted when absent.
units	string	Length unit of coordinates, e.g. "mm". Omitted when absent.
source_hash	string	Hex content hash of the source design. Omitted when absent.
invariants	array of string	Declared contract names the toolpath claims to satisfy. Omitted when empty.

3.3 Segment

One resolved move from start to end (absolute coordinates). An axis component is null when undefined before it is first set (e.g. the very first positioning move).

Field	Type	Presence	Notes
start	[number|null; 3]	always	absolute start (x, y, z)
end	[number|null; 3]	always	absolute end (x, y, z)
travel	bool	always	non-extruding positioning move
speed	number	always	feedrate (mm/min)
length	number	always	true path length (arc length for arcs; 0 for a pure position)
volume	number	always	deposited material volume (mm³)
filament	number	always	feedstock length consumed (mm)
width	number | null	always (nullable)	bead width
height	number | null	always (nullable)	layer height
kind	string enum	omitted ⇒ "line"	see §3.4
centre	[number; 2] | null	omitted when null	arc centre (cx, cy); present only for arc
clockwise	bool	omitted ⇒ false	arc direction: true ⇒ G2, false ⇒ G3
temperature	number	omitted when unset	nozzle temperature (°C)
fan	number	omitted when unset	part-cooling fan (0..1)
flow	number	omitted when unset	flow multiplier; default 1.0 is omitted
tool	u32	omitted when unset	active tool index
dwell_s	number	omitted when unset	dwell duration (s); present only for dwell
manual_gcode	string	omitted when unset	verbatim g-code; present only for manualgcode (see §10)
orientation	[number; 3]	omitted when unset	tool-direction unit vector (i,j,k); null/absent ⇒ +Z (3-axis)
control_points	[[number; 3]]	omitted when unset	spline control points; present only for spline

On the JSON wire, fields marked "omitted when unset/null" carry serde skip_serializing_if, so a motion-only toolpath serializes without any channel keys. start, end, width, height are always present but MAY be null (per component for the arrays).

3.4 SegmentKind

The eight resolved primitives. The on-wire encoding differs by format (this asymmetry is normative for v0 — see §10):

Variant	JSON string	DRY0 dictionary string	DRY1 tag (u8)
Line	"line"	line	0
Arc	"arc"	arc	1
Spline	"spline"	spline	2
Dwell	"dwell"	dwell	3
Retract	"retract"	retract	4
Unretract	"unretract"	unretract	5
Deposit	"deposit"	deposit	6
ManualGcode	"manualgcode"	manual_gcode	7

A reader MUST reject any other JSON string, dictionary string, or tag (§11). An external implementation MUST map all three encodings of a given row to the same logical kind.