diff --git a/src/fabledassistant/services/version_pinning.py b/src/fabledassistant/services/version_pinning.py
new file mode 100644
index 0000000..6b32803
--- /dev/null
+++ b/src/fabledassistant/services/version_pinning.py
@@ -0,0 +1,90 @@
+"""Pin/unpin and auto-pin operations on NoteVersion.
+
+The autosave-rolling system in `services/note_versions.py` continues to
+own the existing rolling-cap behavior; this module adds the manual-pin
+API and the daily auto-pin scan.
+
+Tiers (pin_kind values):
+  None     → rolling autosave; capped at MAX_VERSIONS, FIFO.
+  "auto"   → system-declared via the stability scan; capped at MAX_AUTO_PINS, FIFO.
+  "manual" → user-declared; unlimited, never pruned.
+
+Design: docs/superpowers/specs/2026-05-13-note-version-pinning-design.md
+"""
+from __future__ import annotations
+
+import datetime
+import logging
+from datetime import timezone
+
+from sqlalchemy import select, text
+
+from fabledassistant.models import async_session
+from fabledassistant.models.note_version import NoteVersion
+
+logger = logging.getLogger(__name__)
+
+MAX_AUTO_PINS = 25
+AUTO_PIN_STABILITY_DAYS = 2
+PIN_LABEL_MAX_LEN = 500
+
+
+async def pin_version(
+    user_id: int, note_id: int, version_id: int, *, label: str | None,
+) -> NoteVersion | None:
+    """Mark a version as manually pinned. Returns the updated row or None
+    if not found (or wrong user/note scope).
+
+    Acceptable on already-pinned rows (manual or auto) — promotes to
+    manual and updates the label. Labels are capped at PIN_LABEL_MAX_LEN
+    chars; longer values raise ValueError.
+    """
+    if label is not None and len(label) > PIN_LABEL_MAX_LEN:
+        raise ValueError(
+            f"pin_label too long ({len(label)} > {PIN_LABEL_MAX_LEN} chars)"
+        )
+    async with async_session() as session:
+        version = (
+            await session.execute(
+                select(NoteVersion).where(
+                    NoteVersion.id == version_id,
+                    NoteVersion.note_id == note_id,
+                    NoteVersion.user_id == user_id,
+                )
+            )
+        ).scalars().first()
+        if version is None:
+            return None
+        version.pin_kind = "manual"
+        version.pin_label = label
+        await session.commit()
+        await session.refresh(version)
+        return version
+
+
+async def unpin_version(
+    user_id: int, note_id: int, version_id: int,
+) -> NoteVersion | None:
+    """Clear pin_kind and pin_label, downgrading the row to rolling.
+
+    Does NOT delete the row. If the row is older than the rolling cap
+    depth, the next create_version call will prune it via the rolling
+    FIFO. Returns the updated row or None if not found.
+    """
+    async with async_session() as session:
+        version = (
+            await session.execute(
+                select(NoteVersion).where(
+                    NoteVersion.id == version_id,
+                    NoteVersion.note_id == note_id,
+                    NoteVersion.user_id == user_id,
+                )
+            )
+        ).scalars().first()
+        if version is None:
+            return None
+        version.pin_kind = None
+        version.pin_label = None
+        await session.commit()
+        await session.refresh(version)
+        return version
diff --git a/tests/test_version_pinning_pin_unpin.py b/tests/test_version_pinning_pin_unpin.py
new file mode 100644
index 0000000..d018640
--- /dev/null
+++ b/tests/test_version_pinning_pin_unpin.py
@@ -0,0 +1,128 @@
+"""Tests for manual pin / unpin on note versions."""
+from unittest.mock import AsyncMock, MagicMock, patch
+
+
+def _mock_session_for_version(mock_version):
+    mock_session = AsyncMock()
+    result = MagicMock()
+    result.scalars.return_value.first.return_value = mock_version
+    mock_session.execute = AsyncMock(return_value=result)
+    mock_session.commit = AsyncMock()
+    mock_session.refresh = AsyncMock()
+    mock_session.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_session.__aexit__ = AsyncMock(return_value=False)
+    return mock_session
+
+
+async def test_pin_version_sets_manual_kind_and_label():
+    mock_version = MagicMock()
+    mock_version.pin_kind = None
+    mock_version.pin_label = None
+
+    with patch(
+        "fabledassistant.services.version_pinning.async_session",
+        return_value=_mock_session_for_version(mock_version),
+    ):
+        from fabledassistant.services.version_pinning import pin_version
+        result = await pin_version(
+            user_id=1, note_id=42, version_id=7, label="the runbook circa Q2",
+        )
+
+    assert result is mock_version
+    assert mock_version.pin_kind == "manual"
+    assert mock_version.pin_label == "the runbook circa Q2"
+
+
+async def test_pin_version_accepts_null_label():
+    """label is optional — pinning with no label is allowed."""
+    mock_version = MagicMock()
+    mock_version.pin_kind = None
+    mock_version.pin_label = None
+
+    with patch(
+        "fabledassistant.services.version_pinning.async_session",
+        return_value=_mock_session_for_version(mock_version),
+    ):
+        from fabledassistant.services.version_pinning import pin_version
+        await pin_version(user_id=1, note_id=42, version_id=7, label=None)
+
+    assert mock_version.pin_kind == "manual"
+    assert mock_version.pin_label is None
+
+
+async def test_pin_version_promotes_auto_to_manual_with_label_update():
+    """Pinning an already-auto-pinned version promotes it and updates label."""
+    mock_version = MagicMock()
+    mock_version.pin_kind = "auto"
+    mock_version.pin_label = "stable 2026-04-01 → 2026-04-05"
+
+    with patch(
+        "fabledassistant.services.version_pinning.async_session",
+        return_value=_mock_session_for_version(mock_version),
+    ):
+        from fabledassistant.services.version_pinning import pin_version
+        await pin_version(
+            user_id=1, note_id=42, version_id=7, label="post-network-refresh",
+        )
+
+    assert mock_version.pin_kind == "manual"
+    assert mock_version.pin_label == "post-network-refresh"
+
+
+async def test_pin_version_rejects_overlong_label():
+    """Labels are capped at 500 chars to keep the UI sane."""
+    mock_version = MagicMock()
+    mock_version.pin_kind = None
+
+    # The cap is checked before any DB access, so the session shouldn't
+    # even be entered. We still patch it to avoid accidental DB lookups
+    # if the implementation order changes.
+    with patch(
+        "fabledassistant.services.version_pinning.async_session",
+        return_value=_mock_session_for_version(mock_version),
+    ):
+        from fabledassistant.services.version_pinning import pin_version
+        try:
+            await pin_version(
+                user_id=1, note_id=42, version_id=7, label="x" * 501,
+            )
+            assert False, "expected ValueError"
+        except ValueError as e:
+            assert "500" in str(e) or "long" in str(e).lower()
+
+
+async def test_pin_version_returns_none_when_not_found():
+    mock_session = AsyncMock()
+    result = MagicMock()
+    result.scalars.return_value.first.return_value = None
+    mock_session.execute = AsyncMock(return_value=result)
+    mock_session.commit = AsyncMock()
+    mock_session.refresh = AsyncMock()
+    mock_session.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_session.__aexit__ = AsyncMock(return_value=False)
+
+    with patch(
+        "fabledassistant.services.version_pinning.async_session",
+        return_value=mock_session,
+    ):
+        from fabledassistant.services.version_pinning import pin_version
+        out = await pin_version(user_id=1, note_id=42, version_id=99, label=None)
+
+    assert out is None
+
+
+async def test_unpin_version_clears_kind_and_label():
+    mock_version = MagicMock()
+    mock_version.pin_kind = "manual"
+    mock_version.pin_label = "previous label"
+
+    with patch(
+        "fabledassistant.services.version_pinning.async_session",
+        return_value=_mock_session_for_version(mock_version),
+    ):
+        from fabledassistant.services.version_pinning import unpin_version
+        result = await unpin_version(user_id=1, note_id=42, version_id=7)
+
+    assert result is mock_version
+    assert mock_version.pin_kind is None
+    assert mock_version.pin_label is None