Finalize MDFC follow-ups, docs, and diagnostics tooling

document deck summary DFC badges, exporter annotations, and per-face metadata across README/DOCKER/release notes

record completion of all MDFC roadmap follow-ups and add the authoring guide for multi-face CSV entries

wire in optional DFC_PER_FACE_SNAPSHOT env support, exporter regression tests, and diagnostics updates noted in the changelog

code/tests/test_export_mdfc_annotations.py

@@ -0,0 +1,80 @@
+from __future__ import annotations
+
+import csv
+from pathlib import Path
+
+import pytest
+
+from code.deck_builder.phases.phase6_reporting import ReportingMixin
+
+
+class DummyBuilder(ReportingMixin):
+    def __init__(self) -> None:
+        self.card_library = {
+            "Valakut Awakening // Valakut Stoneforge": {
+                "Card Type": "Instant",
+                "Count": 2,
+                "Mana Cost": "{2}{R}",
+                "Mana Value": "3",
+                "Role": "",
+                "Tags": [],
+            },
+            "Mountain": {
+                "Card Type": "Land",
+                "Count": 1,
+                "Mana Cost": "",
+                "Mana Value": "0",
+                "Role": "",
+                "Tags": [],
+            },
+        }
+        self.color_identity = ["R"]
+        self.output_func = lambda *_args, **_kwargs: None  # silence export logs
+        self._full_cards_df = None
+        self._combined_cards_df = None
+        self.custom_export_base = "test_dfc_export"
+
+
+@pytest.fixture()
+def builder(monkeypatch: pytest.MonkeyPatch) -> DummyBuilder:
+    matrix = {
+        "Valakut Awakening // Valakut Stoneforge": {
+            "R": 1,
+            "_dfc_land": True,
+            "_dfc_counts_as_extra": True,
+        },
+        "Mountain": {"R": 1},
+    }
+
+    def _fake_compute(card_library, *_args, **_kwargs):
+        return matrix
+
+    monkeypatch.setattr(
+        "deck_builder.builder_utils.compute_color_source_matrix",
+        _fake_compute,
+    )
+    return DummyBuilder()
+
+
+def test_export_decklist_csv_includes_dfc_note(tmp_path: Path, builder: DummyBuilder) -> None:
+    csv_path = Path(builder.export_decklist_csv(directory=str(tmp_path)))
+    with csv_path.open("r", encoding="utf-8", newline="") as handle:
+        reader = csv.DictReader(handle)
+        rows = {row["Name"]: row for row in reader}
+
+    valakut_row = rows["Valakut Awakening // Valakut Stoneforge"]
+    assert valakut_row["DFCNote"] == "MDFC: Adds extra land slot"
+
+    mountain_row = rows["Mountain"]
+    assert mountain_row["DFCNote"] == ""
+
+
+def test_export_decklist_text_appends_dfc_annotation(tmp_path: Path, builder: DummyBuilder) -> None:
+    text_path = Path(builder.export_decklist_text(directory=str(tmp_path)))
+    lines = text_path.read_text(encoding="utf-8").splitlines()
+
+    valakut_line = next(line for line in lines if line.startswith("2 Valakut Awakening"))
+    assert "[MDFC: Adds extra land slot]" in valakut_line
+
+    mountain_line = next(line for line in lines if line.strip().endswith("Mountain"))
+    assert "MDFC" not in mountain_line