OpenNest/docs/nest-file-format.md

Nest file format and saved cutting state

.nest is a ZIP archive with additive version-2 JSON metadata in nest.json. Old files remain readable. Older applications ignore the new cutting-state fields; opening and saving with an older application loses that state.

Programs and placements

• programs/program-N is drawing N's clean G-code program; optional programs/program-N-subs contains its hole sub-programs.
• Each serialized plate has a one-based id. Its parts array excludes cut-offs; each placement retains drawingId, x, y, and rotation (radians).
• A placement with HasManualLeadIns also writes parts/plate-P/part-K, and parts/plate-P/part-K-subs when it has hole sub-programs. P is the serialized plate ID; K is the zero-based index in that plate's serialized parts array. Empty plates and cut-offs do not consume these part indices.
• The placement's program field references that ZIP entry. Its G-code is saved in the already-rotated local part frame, with the placed origin at (x, y). Existing :LEADIN, :LEADOUT, and other layer tags, tab gaps, and G65 calls are retained rather than regenerated by a cutting strategy during load. Hole IDs may be negative: they are identifiers, not validity sentinels.
• drawingHash protects against restoring obsolete cutting paths after an externally edited drawing. It is uppercase SHA-256 of UTF-8 text composed of the main text's decimal UTF-16 character count, :, main text, and sub-program text (empty when absent). The hash includes both drawing entries so changing a hole alone invalidates the placed cutting program. Text is read without a BOM; otherwise whitespace and line endings participate in the hash.

The reader constructs and places a clean part first, then installs its saved program without rotating it again. The drawing reference remains authoritative for Remove Lead-ins: removing them restores the clean drawing at the saved pose. Successful restoration marks the part as carrying lead-ins and restores its leadInsLocked flag. The per-part CuttingParameters reference remains null; the saved program, not strategy regeneration, determines the cutting geometry.

Missing program references in legacy files load clean and silently, even when old transient flags were true. A missing or mismatched drawing hash likewise loads clean silently. A referenced but missing, unparseable, or motionless part program, or an unresolved/empty hole sub-program, leaves that part clean and unlocked without discarding the rest of the nest. NestReader.Warnings identifies the plate, zero-based part index, and entry; File > Open displays these warnings. The program reader is not a general G-code or geometric safety validator; the saved cutting geometry is not validated against the drawing.

Plate cutting parameters

Each plate's optional cuttingParameters stores the settings used by Assign Lead-ins and Place Lead-in. Missing settings stay null, preserving the old default selection behavior. OpenNest.IO.CuttingParametersSerializer owns the shared cross-platform DTO mapping; the desktop settings serializer delegates to it so existing saved settings keep their JSON contract. Settings are independent of the saved part programs: restoring settings never regenerates those programs.

Drawing edits

DrawingProgramSnapshot captures serialized main and hole-program text before the converter is loaded. After an accepted edit, only parts referencing drawings whose program text changed are rebuilt (lead-ins, tabs, and locks cleared); their location and rotation remain unchanged. Reference identity, not editable names, keys this comparison. The desktop invalidates the affected layout graphics. Name, quantity, and color edits leave placed programs alone. The properties editor previously called LayoutPart.Update, a color refresh, not Part.Update; it now explicitly refreshes only the edited drawing's layout colors.

Verification and limits

The automated tests cover save/reopen/re-save, rotated/manual/locked parts, lead-outs and tab gaps, hole binding, clean removal, stale drawings, damaged entries isolated from other parts, plate settings, and CI Fiber posting before and after reload. Drawing-change decision logic runs on Linux; desktop rendering, dialog values, and clicks require Windows acceptance.

Known separate issue: the cutting strategy currently labels contour cuts Display. CI Fiber includes them, but GravographIS skips Display. Saving restores the existing layers; this change does not alter the strategy or either post. Future hardening: make numeric G-code serialization/parsing culture-invariant as a coordinated compatibility change; do not change just one side. Program content deduplication is optional and must not change per-part ownership.