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title: "Impose producer" description: "Sheet-level step-and-repeat. Layout solved by codex_pdf.geom.tile_grid; Compile drops cells onto sheets via pikepdf. No Compile-side layout math." group: "Reference" order: 12

Impose producer

compile_pdf.impose takes a 1-up input PDF and produces a sheet-level imposition: step-and-repeat across columns × rows, with optional work-and-turn / tumble back-side handling and bleed expansion.

The layout itself comes from Codex. Compile asks codex_pdf.geom.tile_grid() for the per-cell placement plan, then drops each cell onto the sheet with pikepdf. No Compile-side layout math — that's a hard architectural rule, enforced by the audit script.

Layout schema

{
  "schema_version": "1.0.0",
  "sheet": { "width_pt": 1782, "height_pt": 1224 },
  "cell":  { "width_pt":  612, "height_pt":  792 },
  "grid":  { "cols": 3, "rows": 2, "gutter_pt": 12 },
  "bleed_handling": "overlap",
  "cell_rotation": 0,
  "flip_per_row": false,
  "back_side": { "mode": "work-and-turn" }
}

Fields:

Field	Values	Notes
bleed_handling	overlap / mirror / none	overlap = shared bleed across cells; mirror = reflected bleed; none = hard cut
cell_rotation	0 / 90 / 180 / 270	Per-cell rotation, applied uniformly
flip_per_row	true / false	Useful for fold-after layouts
back_side.mode	work-and-turn / work-and-tumble / none	How the back side relates to the front

The combination of these fields exercises codex 1.4.0+'s GEOM schema 1.1.0 extension (cell_rotation, flip_per_row, bleed_handling, CellPlacement).

Codex surface consumed

• codex_pdf.geom.tile_grid — the canonical step-and-repeat solver.
• codex_pdf.geom.TileGrid — input shape.
• codex_pdf.geom.TileResult — output container with cell_placements: list[CellPlacement].
• codex_pdf.geom.CellPlacement — per-cell anchor + transform.

Cell-extract round-trip

A determinism property unique to impose: extracting cell N from the imposed sheet must reproduce the original Nth input page byte-for-byte. The verifier runs this check in CI for every impose --layout test fixture.

Retention-for-training

POST /v1/impose/apply honours X-Compile-Retain-For-Training. See operations/retention.md.

Status

Shipped. POST /v1/impose/apply is live; cell-extract round-trip verification runs in CI on every release.