diff --git a/examples/ingest-golden-file/expected-bundle/index.md b/examples/ingest-golden-file/expected-bundle/index.md
new file mode 100644
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+++ b/examples/ingest-golden-file/expected-bundle/index.md
@@ -0,0 +1,3 @@
+Golden extraction case: two CSV extracts from a local project archive (file source type).
+- [Project costs](ingest-costs.md)
+- [Escaping edge cases](ingest-edge.md)
diff --git a/examples/ingest-golden-file/expected-bundle/ingest-costs.md b/examples/ingest-golden-file/expected-bundle/ingest-costs.md
new file mode 100644
index 0000000..fa542d7
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+++ b/examples/ingest-golden-file/expected-bundle/ingest-costs.md
@@ -0,0 +1,14 @@
+---
+type: dataset
+title: Project costs
+source_system: prosjekt-arkiv
+source_query: costs.csv
+ingested_at: 2026-07-03T12:00:00Z
+ingest_manifest: manifest@24109f486b9ef708
+generated: true
+---
+
+| item | cost_nok | note |
+| --- | --- | --- |
+| led-retrofit | 120000 | ROI under 2 years |
+| hvac-tuning | 80000 | requires vendor quote |
diff --git a/examples/ingest-golden-file/expected-bundle/ingest-edge.md b/examples/ingest-golden-file/expected-bundle/ingest-edge.md
new file mode 100644
index 0000000..47da3d7
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+++ b/examples/ingest-golden-file/expected-bundle/ingest-edge.md
@@ -0,0 +1,18 @@
+---
+type: reference
+title: Escaping edge cases
+source_system: prosjekt-arkiv
+source_query: edge.csv
+ingested_at: 2026-07-03T12:00:00Z
+ingest_manifest: manifest@24109f486b9ef708
+generated: true
+---
+
+| id | value |
+| --- | --- |
+| backslash | a\\b |
+| pipe | a\|b |
+| newline | x y |
+| both | \\\| |
+| zeros | 007 |
+| decimal | 1.50 |
diff --git a/examples/ingest-golden-file/fixture/costs.csv b/examples/ingest-golden-file/fixture/costs.csv
new file mode 100644
index 0000000..0dbc341
--- /dev/null
+++ b/examples/ingest-golden-file/fixture/costs.csv
@@ -0,0 +1,3 @@
+item,cost_nok,note
+led-retrofit,120000,ROI under 2 years
+hvac-tuning,80000,requires vendor quote
diff --git a/examples/ingest-golden-file/fixture/edge.csv b/examples/ingest-golden-file/fixture/edge.csv
new file mode 100644
index 0000000..e3fb623
--- /dev/null
+++ b/examples/ingest-golden-file/fixture/edge.csv
@@ -0,0 +1,8 @@
+id,value
+backslash,a\b
+pipe,a|b
+newline,"x
+y"
+both,\|
+zeros,007
+decimal,1.50
diff --git a/examples/ingest-golden-file/ingested-at.txt b/examples/ingest-golden-file/ingested-at.txt
new file mode 100644
index 0000000..9f82d47
--- /dev/null
+++ b/examples/ingest-golden-file/ingested-at.txt
@@ -0,0 +1 @@
+2026-07-03T12:00:00Z
diff --git a/examples/ingest-golden-file/manifest.json b/examples/ingest-golden-file/manifest.json
new file mode 100644
index 0000000..5c3a087
--- /dev/null
+++ b/examples/ingest-golden-file/manifest.json
@@ -0,0 +1,21 @@
+{
+  "manifest_version": 1,
+  "source": {"type": "file", "id": "prosjekt-arkiv", "root": "fixture"},
+  "bundle_summary": "Golden extraction case: two CSV extracts from a local project archive (file source type).",
+  "extractions": [
+    {
+      "id": "costs",
+      "title": "Project costs",
+      "query": "costs.csv",
+      "okf_type": "dataset",
+      "max_rows": 10
+    },
+    {
+      "id": "edge",
+      "title": "Escaping edge cases",
+      "query": "edge.csv",
+      "okf_type": "reference",
+      "max_rows": 10
+    }
+  ]
+}
diff --git a/tests/test_ingest_golden.py b/tests/test_ingest_golden.py
new file mode 100644
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+++ b/tests/test_ingest_golden.py
@@ -0,0 +1,39 @@
+"""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