Rewrite producer

compile_pdf.rewrite applies object-tree mutations to a single PDF input. The output is a single PDF with the requested mutations applied and everything else byte-identical to the input — that “nothing else touched” guarantee is mechanically verified.

What it does

15 in-scope mutations grouped by category:

Structural

OCG flips — toggle Optional Content Group visibility per layer.
Page lifecycle ops — insert / delete / reorder / rotate pages.
Box adjustments — trim, bleed, art, crop, media boxes.
Page-label surgery — fix 1, 2, i, ii, … numbering.

Hygiene

Metadata patches — Info dict + XMP. Strip / set / replace.
Color-space swaps — DeviceRGB → DeviceCMYK pin (or inverse).
Strip JS — remove /JavaScript actions and /JS keys.
Strip embedded files — remove /EmbeddedFiles.
Normalize page-tree fan-out — flatten deep trees.

Lifecycle

PDF/X version pin — declare conformance level.
Producer / Creator stamping — operator provenance.

What it doesn’t do

Out of scope, gated by a hard STOP-gate in the audit:

Content-stream surgery
Font subsetting / embedding changes
Image recompression
Color reflow

These belong to a future producer (or never — see the design spec for the rationale).

Plan schema

A rewrite plan is a JSON document. Top-level fields:

{
  "schema_version": "1.0.0",
  "ops": [
    { "op": "ocg_flip",          "layer": "Bleed",            "visible": false },
    { "op": "metadata_set",      "key": "Title",              "value": "Job 12345" },
    { "op": "metadata_strip",    "keys": ["JS", "JavaScript"] },
    { "op": "page_rotate",       "page": 1, "degrees": 90 },
    { "op": "box_set",           "page": 2, "box": "TrimBox",  "rect_pt": [0, 0, 612, 792] }
  ]
}

Schema documented at compile-pdf schema rewrite. Validation runs client-side (CLI) and server-side (POST /v1/rewrite/apply).

Determinism guarantee

Same input + same plan produces byte-identical output (verified by SHA-256). The cache key composer (src/compile_pdf/cache.py) includes the canonical plan hash, so re-running an identical request short-circuits to the cached output.

Codex surface consumed

codex_pdf.CodexDocument — Compile reads the document to validate page-index references in the plan (“you can’t delete page 12 of a 10-page PDF”).

No re-implementation; the audit script enforces.

Retention-for-training

POST /v1/rewrite/apply honours the X-Compile-Retain-For-Training header. When truthy and COMPILE_RETAIN_BUCKET is configured, the call’s input/output/result triplet is persisted to S3-compatible storage with a TTL tag. The decision is reflected on the lineage record. See operations/retention.md.

Status

Shipped. The mutation engine (pikepdf) + three-layer verify + POST /v1/rewrite/apply are live; determinism is enforced in CI.