[cyrilcaoyang]

Summary

• POST /submissions takes an optional placement for an .stl the gateway slices: auto (default, centred by the slicer) or front_left (footprint slicer.placement_margin_mm, default 10 mm, in from the front-left corner of the printable area, resting on the plate, orientation unchanged). The mesh is wrapped in a one-object 3MF whose build transform carries the offset and sliced with --arrange 0. A part that does not fit, an unreadable STL, or placement on an already-sliced .3mf/.gcode → 422.
• New per-printer slicer.machine_profiles.<id>.end_bed_y_mm rewrites the Y of the stock end gcode's final park move (A1: G1 X-48 Y180 F3600, just before M18) so the finished plate is presented forward. Values outside the printable area, or end gcode without that move, are refused rather than guessed. Recorded as provenance.end_bed_y_mm and returned by pickup-targets as bed_park_y_mm.
• Docs: README, API reference, agent guide, printers.example.yaml.

Robot pickup impact

Bed-frame object positions are unchanged. On the A1 the bed moves in Y, so parking at Y250 instead of the stock Y180 puts the plate and every object 70 mm further toward the front of the printer. The arm agent should use bed_park_y_mm (null = unknown/stock) in its transform. Motors are released after the print, so the bed can still be pushed.

Safety scope

No new control verb and no gate relaxed: both changes only alter the slice the gateway produces; nothing here sends a printer command. Y250 is within the A1's normal travel (its own start gcode moves to G1 Y250). The user confirmed the forward park position will not hit the robot.

Test plan

• uv run pytest -q — 333 passed (14 new)
• uv run ruff check .
• Real Bambu Studio CLI, A1 presets: cube authored at (100, 150) slices to bed X/Y 10–30 mm (first-layer toolpath 10.3–29.7); auto still centres at 118–138; end gcode ends G1 X-48 Y250 F3600 before M18
• First hardware print on bambu_a1_01 with placement=front_left and end_bed_y_mm: 250

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