feat(extract): implement pdf behind the [extract] extra with pdfplumber

Order G2a. Populates the optional `[extract]` extra for the first time with
one parser, `pdfplumber>=0.11.10,<0.12` (MIT), and wires `pdf` through it.
The default install is untouched: exactly one runtime dependency, stdlib
otherwise, enforced by test_packaging.py.

The gate for `pdf` becomes an import probe rather than a frozenset membership
test, exactly as extract.py's docstring had promised. The rejection does not
change: without the extra, `pdf` still raises `extractor_extra_missing` with
the same message. That behaviour is asserted UNCONDITIONALLY via a sys.modules
monkeypatch, so it holds on machines where the parser is installed too — a
skip would have preserved nothing there. Verified in a clean venv without the
extra: 589 passed, 7 skipped; with it, 596 passed.

`docx`/`xlsx` are unchanged and still fail fast — the extra names exactly what
it ships.

The parser choice was forced by measurement, not preference (b73dd9d,
docs/2026-08-21-g2-pdf-extraction-measurement.md): on a real requirement table
pdfplumber keeps 4 of 4 rows with label and value on one line, where pypdf,
pdfminer.six and pymupdf each keep 0 of 4. pymupdf is additionally out on
licence (AGPL-3.0), which an MIT package must not push onto a consumer.

Three facts from that measurement are now carried in code rather than in a
report:

- Extracted text is pinned to an exact transitive parser version
  (pdfplumber pins pdfminer.six==20260107; date-stamped, no stability
  contract). tests/test_extract.py freezes the expected text of a committed
  hand-written fixture so a parser upgrade breaks something visible instead of
  drifting silently. Reasoning at the declaration site and in
  tests/fixtures/README.md.
- Determinism within a version is now held by a test, not only measured once.
- Drawn content does not survive extraction. Every pdf extraction emits the
  new `ExtractionWarning`: figures have no text to recover, so a bundle built
  from drawn documents is incomplete by construction. Stated categorically
  rather than detected — deciding "is there a figure here" is the layout
  heuristic G2b declined.

Two new error codes, both mirroring existing patterns: `extractor_empty_pdf`
(a scanned/image-only PDF, refused rather than persisted as an empty concept)
and `extractor_pdf_error` (parser failure wrapped, never leaked).

Structured table recovery (G2b) is NOT implemented and is documented as out of
scope: two independent parsers return the same wrong shape, so the breakage is
document geometry, not a library choice. PDFs enter as prose.

Also corrects an install promise this change would otherwise have published:
the README no longer presents a bare `pip install 'llm-ingestion-okf[extract]'`
as working, because the package is not on an index.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HtNhsdHnMGtMi7U2mvMU8z

tests/fixtures/README.md

@@ -0,0 +1,53 @@
+# Test fixtures
+
+## The PDF fixtures
+
+`two-line-krav.pdf` and `no-text-layer.pdf` are hand-written minimal PDFs,
+regenerated by `make_fixtures.py` in this directory:
+
+```
+python3 tests/fixtures/make_fixtures.py
+```
+
+They carry no library's output — the objects are laid out by hand and the xref
+offsets computed from the emitted bytes — so they are auditable byte for byte
+and reproducible from that one file.
+
+| Fixture | What it is for |
+|---|---|
+| `two-line-krav.pdf` | One heading plus one requirement row with label and value on the **same line**. That pairing is the property `pdfplumber` was chosen for. |
+| `no-text-layer.pdf` | A structurally valid page with no text operators — the shape a scanned or image-only PDF presents. Must fail fast (`extractor_empty_pdf`), never persist as an empty concept. |
+
+## Why the expected PDF text is frozen as a literal
+
+`tests/test_extract.py` asserts the extracted text of `two-line-krav.pdf` as an
+exact string. That is deliberate, and it is the mechanism behind a promise this
+library makes everywhere else:
+
+- Extraction is deterministic **within** a parser version. Measured 2026-08-21
+  across five configurations, two runs each, compared byte for byte
+  (`docs/2026-08-21-g2-pdf-extraction-measurement.md`).
+- Extraction is **not** guaranteed stable **across** parser versions.
+  `pdfplumber` pins `pdfminer.six==20260107` exactly, and `pdfminer.six` ships
+  date-stamped releases with no stability contract. So the real pin on extracted
+  text is a transitive one, and it is exact.
+
+The consequence is worth stating plainly: **any golden fixture built on
+extracted PDF text is pinned to an exact parser version, and a parser upgrade
+is a fixture migration, not a routine bump.** The frozen literal is what makes
+that upgrade break something visible instead of drifting silently. If it goes
+red after a dependency change, the correct response is to read the diff and
+decide, not to re-record the expectation.
+
+The version range that carries this lives in `pyproject.toml`'s
+`[project.optional-dependencies] extract`, with the same reasoning at the
+declaration site.
+
+## What these fixtures do not cover
+
+Structured table recovery. Measured on real Vegnormalene, only 45 of 196
+detected table objects are clean enough to hand to `render_table` unchanged;
+two independent parsers return the same wrong shape, because the breakage is in
+the documents' ruling geometry rather than in either library. PDFs enter this
+library as **prose**, and structured tables are out of scope until that is
+decided separately.

tests/fixtures/make_fixtures.py

@@ -0,0 +1,64 @@
+"""Regenerate the committed PDF fixtures for tests/test_extract.py.
+
+Hand-written minimal PDFs: objects laid out by hand, xref offsets computed
+from the emitted bytes. No generator library, so the fixtures are auditable
+byte for byte and reproducible from this file alone.
+
+Run from the repository root:  python3 tests/fixtures/make_fixtures.py
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+HERE = Path(__file__).parent
+
+# Two text lines: a heading, and one requirement row with label and value on
+# the SAME line. That pairing is the property the parser choice was made on
+# (see docs/2026-08-21-g2-pdf-extraction-measurement.md), so the fixture
+# fails visibly if a parser upgrade ever breaks it. Byte 0xE5 is the Norwegian
+# 'a-ring' in WinAnsiEncoding, which the font object below declares.
+KRAV_CONTENT = (
+    b"BT /F1 12 Tf 20 160 Td (Krav til helning p\xe5 utkilingen) Tj ET\n"
+    b"BT /F1 12 Tf 20 140 Td (60 og 70 1:15) Tj ET\n"
+)
+
+# A structurally valid page carrying no text operators at all -- the shape a
+# scanned or image-only PDF presents to a text extractor.
+NO_TEXT_CONTENT = b"20 20 160 160 re S\n"
+
+
+def build_pdf(content: bytes) -> bytes:
+    """Assemble a one-page PDF around `content` as the page content stream."""
+    objects = [
+        b"<< /Type /Catalog /Pages 2 0 R >>",
+        b"<< /Type /Pages /Kids [3 0 R] /Count 1 >>",
+        b"<< /Type /Page /Parent 2 0 R /MediaBox [0 0 200 200] "
+        b"/Contents 4 0 R /Resources << /Font << /F1 5 0 R >> >> >>",
+        b"<< /Length " + str(len(content)).encode() + b" >>\nstream\n" + content + b"endstream",
+        b"<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >>",
+    ]
+
+    out = bytearray(b"%PDF-1.4\n")
+    offsets = []
+    for number, body in enumerate(objects, start=1):
+        offsets.append(len(out))
+        out += str(number).encode() + b" 0 obj\n" + body + b"\nendobj\n"
+
+    xref_at = len(out)
+    size = str(len(objects) + 1).encode()
+    out += b"xref\n0 " + size + b"\n0000000000 65535 f \n"
+    for offset in offsets:
+        out += ("%010d 00000 n \n" % offset).encode()
+    out += b"trailer\n<< /Size " + size + b" /Root 1 0 R >>\n"
+    out += b"startxref\n" + str(xref_at).encode() + b"\n%%EOF\n"
+    return bytes(out)
+
+
+if __name__ == "__main__":
+    for name, content in (
+        ("two-line-krav.pdf", KRAV_CONTENT),
+        ("no-text-layer.pdf", NO_TEXT_CONTENT),
+    ):
+        (HERE / name).write_bytes(build_pdf(content))
+        print(f"wrote {name}")

tests/fixtures/no-text-layer.pdf

@@ -0,0 +1,32 @@
+%PDF-1.4
+1 0 obj
+<< /Type /Catalog /Pages 2 0 R >>
+endobj
+2 0 obj
+<< /Type /Pages /Kids [3 0 R] /Count 1 >>
+endobj
+3 0 obj
+<< /Type /Page /Parent 2 0 R /MediaBox [0 0 200 200] /Contents 4 0 R /Resources << /Font << /F1 5 0 R >> >> >>
+endobj
+4 0 obj
+<< /Length 19 >>
+stream
+20 20 160 160 re S
+endstream
+endobj
+5 0 obj
+<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >>
+endobj
+xref
+0 6
+0000000000 65535 f 
+0000000009 00000 n 
+0000000058 00000 n 
+0000000115 00000 n 
+0000000241 00000 n 
+0000000309 00000 n 
+trailer
+<< /Size 6 /Root 1 0 R >>
+startxref
+406
+%%EOF

tests/fixtures/two-line-krav.pdf

@@ -0,0 +1,33 @@
+%PDF-1.4
+1 0 obj
+<< /Type /Catalog /Pages 2 0 R >>
+endobj
+2 0 obj
+<< /Type /Pages /Kids [3 0 R] /Count 1 >>
+endobj
+3 0 obj
+<< /Type /Page /Parent 2 0 R /MediaBox [0 0 200 200] /Contents 4 0 R /Resources << /Font << /F1 5 0 R >> >> >>
+endobj
+4 0 obj
+<< /Length 107 >>
+stream
+BT /F1 12 Tf 20 160 Td (Krav til helning på utkilingen) Tj ET
+BT /F1 12 Tf 20 140 Td (60 og 70 1:15) Tj ET
+endstream
+endobj
+5 0 obj
+<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >>
+endobj
+xref
+0 6
+0000000000 65535 f 
+0000000009 00000 n 
+0000000058 00000 n 
+0000000115 00000 n 
+0000000241 00000 n 
+0000000398 00000 n 
+trailer
+<< /Size 6 /Root 1 0 R >>
+startxref
+495
+%%EOF