test(ingest): golden extraction case examples/ingest-golden-file, byte-frozen (I2)

tests/test_ingest_golden.py

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+"""I2 golden regression — the §11 golden extraction case, byte-for-byte.
+
+The golden case pins every determinism decision the unit tests exercise as RULES: the
+text-verbatim CSV reading (the ``007``/``1.50`` cells discriminate it from a
+number-normalizing implementation — their normalized forms differ byte-wise), the escape
+order, the §5 frontmatter layout, and the §6 index shape. RED when ANY byte of the expected
+bundle diverges (spec §11 "Golden regression" seam). The fixture layout is the shared
+convention (``manifest.json``, ``fixture/``, ``ingested-at.txt``, ``expected-bundle/``);
+authored LOCALLY in I2 — sharing via commons is a later gated round.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from portfolio_optimiser.ingest import materialize
+
+GOLDEN = Path(__file__).resolve().parents[1] / "examples" / "ingest-golden-file"
+
+
+def _bundle_bytes(directory: Path) -> dict[str, bytes]:
+    return {p.name: p.read_bytes() for p in sorted(directory.iterdir()) if p.is_file()}
+
+
+def test_golden_extraction_is_bit_deterministic(tmp_path: Path) -> None:
+    ingested_at = (GOLDEN / "ingested-at.txt").read_text(encoding="utf-8").strip()
+    out = tmp_path / "bundle"
+    materialize(GOLDEN / "manifest.json", out, ingested_at=ingested_at)
+
+    expected = _bundle_bytes(GOLDEN / "expected-bundle")
+    actual = _bundle_bytes(out)
+    # File-SET equality first — catches extra AND missing files, not just diverging bytes.
+    assert actual.keys() == expected.keys()
+    for name, content in expected.items():
+        assert actual[name] == content, f"golden byte divergence in {name}"
+
+    # §10: a second run over the same output leaves every byte unchanged.
+    materialize(GOLDEN / "manifest.json", out, ingested_at=ingested_at)
+    assert _bundle_bytes(out) == expected