Auto-Print G-code Injection had two reviewer-reported bugs from the initial
ship:
1. Start snippets were prepended to the entire plate_X.gcode, landing
before the printer's own bed-heat / homing / nozzle-prime sequence —
so a Swapmod start snippet that assumed nozzle-at-temp ran on a cold
printer (pleite). Anchor injection at "; MACHINE_START_GCODE_END" so
snippets land where a slicer-side custom-start-gcode would. Files
without the marker keep prepend behaviour as a fallback with a
warning log.
2. Placeholders like "G1 Z{max_layer_z} F600" were written verbatim;
firmware parsed them as Z1 and crashed the head into the print on
tall models — real safety bug (DevScarabyte). Added a header parser
for the 3MF "; HEADER_BLOCK_START..END" block (lowercased keys,
[units] suffix stripped, spaces -> underscores) and a Prusa-style
{name} substitution pass over both start and end snippets before
injection. Supported placeholders: {max_layer_z} / {max_print_height},
{total_layer_number} / {total_layers}, {total_filament_weight},
{total_filament_length}, plus any other normalised header key.
Unknown placeholders are left verbatim with a warning — a typo never
silently expands to an empty string.
16 new regression tests across 4 new classes in test_gcode_injection.py
(anchored injection + missing-marker fallback, placeholder substitution
including alias resolution + unknown-pass-through, direct unit tests
for each new helper). All 2195 backend unit tests pass.
Wiki print-queue page updated with the supported placeholder list and a
{max_layer_z} safety callout for park moves.
Per-model start/end G-code snippets configurable in Settings (Workflow
tab). Queue items get "Inject G-code" toggle — scheduler injects
snippets into a temp 3MF copy before FTP upload. Supports Farmloop,
SwapMod, AutoClear, Printflow 3D and similar bed-clearing systems.
Original files are never modified.
phieb