diff --git a/CHANGELOG.md b/CHANGELOG.md
index 79d3da40..daa2bf43 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@ Full release notes with details on each version: [GitHub Releases](https://githu
 
 ## Unreleased
 
+- Fix: `to_obsidian` / `to_canvas` / `to_wiki` no longer silently overwrite notes whose labels differ only by case (e.g. a class `References` and a prose heading `references`). The filename dedup was keyed on the exact-case name, so two such labels counted as non-colliding and the second write clobbered the first on case-insensitive filesystems (macOS/APFS, Windows/NTFS) — no suffix, no warning. Dedup now folds case (keyed on the lowercased name) while still emitting the original-case filename, so any pair that would collide on disk gets a numeric suffix. The obsidian/canvas dedup is shared in one helper so they can't drift, `wiki`'s slug dedup gets the matching fix, the `_COMMUNITY_*.md` overview notes (which had no dedup) are covered, and a generated `base_1` is itself re-checked so it can't overwrite a node literally labelled `base_1` (#1453, thanks @TPAteeq).
+
 ## 0.8.49 (2026-06-24)
 
 - Fix: the `get_community` MCP tool now shows the community name in its header (`Community 12 — Auth & Sessions (8 nodes)`), matching `get_node` and the query-traversal output, which already read the `community_name` attribute `to_json` writes onto every node. `get_community` was the only graph tool still returning a bare numeric id. The name is read from the community's member nodes (they share it), sanitised like every other LLM-derived field, and skipped when it is just the `Community N` placeholder so the header never doubles to `Community 12 — Community 12` (#1448, thanks @rmart1308).
diff --git a/graphify/export.py b/graphify/export.py
index 17798d6b..084ba52d 100644
--- a/graphify/export.py
+++ b/graphify/export.py
@@ -840,6 +840,28 @@ def _cap_filename(s: str, limit: int = 200) -> str:
     return f"{truncated}_{digest}"
 
 
+def _dedup_node_filenames(G: nx.Graph, safe_name) -> dict[str, str]:
+    """Map each node_id to a unique note filename, appending a numeric suffix on
+    collision. The collision set is keyed on the lowercased name so two labels
+    differing only by case (e.g. "References" vs "references") still get distinct
+    filenames - on case-insensitive filesystems (macOS/APFS, Windows/NTFS) they
+    would otherwise resolve to one path and silently overwrite each other on disk.
+    The suffixed candidate is itself re-checked, so a generated "base_1" never
+    silently overwrites a node whose literal label is already "base_1"."""
+    node_filenames: dict[str, str] = {}
+    used: set[str] = set()
+    for node_id, data in G.nodes(data=True):
+        base = safe_name(data.get("label", node_id))
+        candidate = base
+        n = 1
+        while candidate.lower() in used:
+            candidate = f"{base}_{n}"
+            n += 1
+        used.add(candidate.lower())
+        node_filenames[node_id] = candidate
+    return node_filenames
+
+
 def to_obsidian(
     G: nx.Graph,
     communities: dict[int, list[str]],
@@ -875,16 +897,7 @@ def to_obsidian(
             return "unnamed"
         return _cap_filename(cleaned)
 
-    node_filename: dict[str, str] = {}
-    seen_names: dict[str, int] = {}
-    for node_id, data in G.nodes(data=True):
-        base = safe_name(data.get("label", node_id))
-        if base in seen_names:
-            seen_names[base] += 1
-            node_filename[node_id] = f"{base}_{seen_names[base]}"
-        else:
-            seen_names[base] = 0
-            node_filename[node_id] = base
+    node_filename = _dedup_node_filenames(G, safe_name)
 
     # Helper: compute dominant confidence for a node across all its edges
     def _dominant_confidence(node_id: str) -> str:
@@ -982,13 +995,33 @@ def to_obsidian(
         }
         return len(neighbor_cids)
 
-    community_notes_written = 0
-    for cid, all_members in communities.items():
-        community_name = (
+    def _community_name(cid) -> str:
+        return (
             community_labels.get(cid, f"Community {cid}")
             if community_labels and cid is not None
             else f"Community {cid}"
         )
+
+    # One case-folded-deduped filename per community, computed once so the note we
+    # write and every [[_COMMUNITY_...]] cross-reference resolve to the same file.
+    # Two community labels differing only by case (e.g. LLM labels "API" vs "Api")
+    # would otherwise overwrite each other on case-insensitive filesystems - and
+    # this path had no dedup at all, so even same-case duplicate labels collided.
+    community_filename: dict = {}
+    used_community: set[str] = set()
+    for cid in communities:
+        base = f"_COMMUNITY_{safe_name(_community_name(cid))}"
+        candidate = base
+        n = 1
+        while candidate.lower() in used_community:
+            candidate = f"{base}_{n}"
+            n += 1
+        used_community.add(candidate.lower())
+        community_filename[cid] = candidate
+
+    community_notes_written = 0
+    for cid, all_members in communities.items():
+        community_name = _community_name(cid)
         # A community's member list can contain ids with no backing node in G
         # (e.g. pruned nodes, stale community assignments from a prior run, or
         # synthesized/merge-artifact ids). Dereferencing those via G.nodes[n] or
@@ -1052,13 +1085,8 @@ def to_obsidian(
         if cross:
             lines.append("## Connections to other communities")
             for other_cid, edge_count in sorted(cross.items(), key=lambda x: -x[1]):
-                other_name = (
-                    community_labels.get(other_cid, f"Community {other_cid}")
-                    if community_labels and other_cid is not None
-                    else f"Community {other_cid}"
-                )
-                other_safe = safe_name(other_name)
-                lines.append(f"- {edge_count} edge{'s' if edge_count != 1 else ''} to [[_COMMUNITY_{other_safe}]]")
+                other_fname = community_filename.get(other_cid) or f"_COMMUNITY_{safe_name(_community_name(other_cid))}"
+                lines.append(f"- {edge_count} edge{'s' if edge_count != 1 else ''} to [[{other_fname}]]")
             lines.append("")
 
         # Top bridge nodes - highest degree nodes that connect to other communities
@@ -1078,8 +1106,7 @@ def to_obsidian(
                     f"{'community' if reach == 1 else 'communities'}"
                 )
 
-        community_safe = safe_name(community_name)
-        fname = f"_COMMUNITY_{community_safe}.md"
+        fname = community_filename[cid] + ".md"
         (out / fname).write_text("\n".join(lines), encoding="utf-8")  # nosec
         community_notes_written += 1
 
@@ -1130,16 +1157,7 @@ def to_canvas(
 
     # Build node_filenames if not provided (same dedup logic as to_obsidian)
     if node_filenames is None:
-        node_filenames = {}
-        seen_names: dict[str, int] = {}
-        for node_id, data in G.nodes(data=True):
-            base = safe_name(data.get("label", node_id))
-            if base in seen_names:
-                seen_names[base] += 1
-                node_filenames[node_id] = f"{base}_{seen_names[base]}"
-            else:
-                seen_names[base] = 0
-                node_filenames[node_id] = base
+        node_filenames = _dedup_node_filenames(G, safe_name)
 
     # Fallback: with no community data (e.g. --no-cluster builds or a missing
     # analysis sidecar) the grid below produces nothing and the canvas is written
diff --git a/graphify/wiki.py b/graphify/wiki.py
index eb662317..4212fb7f 100644
--- a/graphify/wiki.py
+++ b/graphify/wiki.py
@@ -248,12 +248,16 @@ def to_wiki(
     used_slugs: set[str] = set()
 
     def _unique_slug(base: str) -> str:
+        # Fold case in the collision check: two labels differing only by case
+        # (e.g. "Parser" vs "parser") resolve to one path on case-insensitive
+        # filesystems (macOS/APFS, Windows/NTFS), so they must dedup against each
+        # other while still emitting the original-case filename.
         slug = base
         n = 2
-        while slug in used_slugs:
+        while slug.lower() in used_slugs:
             slug = f"{base}_{n}"
             n += 1
-        used_slugs.add(slug)
+        used_slugs.add(slug.lower())
         return slug
 
     # Community articles
diff --git a/tests/test_export.py b/tests/test_export.py
index a77f64dd..e5dbfa43 100644
--- a/tests/test_export.py
+++ b/tests/test_export.py
@@ -237,6 +237,110 @@ def test_to_canvas_never_emits_punctuation_only_filenames():
         assert not bad, f"punctuation-only canvas filenames: {bad}"
 
 
+# ── Case-only-distinct labels must not collide on case-insensitive filesystems ──
+
+def _case_collision_graph():
+    """Two nodes whose labels differ only by case - on macOS/APFS and Windows/NTFS
+    their notes resolve to the same path unless the dedup map folds case."""
+    return build_from_json({
+        "nodes": [
+            {"id": "n1", "label": "References", "file_type": "code", "source_file": "a.py"},
+            {"id": "n2", "label": "references", "file_type": "document", "source_file": "b.md"},
+        ],
+        "edges": [],
+    })
+
+
+def test_to_obsidian_case_only_distinct_labels_dont_overwrite():
+    """Both notes must survive as separate files. On a case-insensitive filesystem
+    a missing suffix silently overwrites the first note (fewer files than nodes);
+    on a case-sensitive one it writes two stems equal under .lower(). Assert both:
+    every node note is on disk, and no two stems collide case-insensitively."""
+    G = _case_collision_graph()
+    communities = cluster(G)
+    with tempfile.TemporaryDirectory() as tmp:
+        to_obsidian(G, communities, tmp)
+        notes = [p for p in Path(tmp).rglob("*.md") if not p.name.startswith("_COMMUNITY")]
+        assert len(notes) == G.number_of_nodes(), [p.name for p in notes]
+        lowered = [p.stem.lower() for p in notes]
+        assert len(set(lowered)) == len(lowered), [p.name for p in notes]
+        # the suffixed name must be the expected one, not merely distinct
+        assert sorted(p.stem for p in notes) == ["References", "references_1"], [p.name for p in notes]
+
+
+def test_to_obsidian_generated_suffix_doesnt_overwrite_literal():
+    """A generated `_1` suffix must not collide with a node whose literal label is
+    already that suffixed name. With labels [dup, dup, dup_1] the second `dup`
+    becomes `dup_1`, which would clobber the third node unless the candidate is
+    re-checked. This collides on case-sensitive filesystems too, so it guards the
+    dedup loop independently of case-folding."""
+    G = build_from_json({
+        "nodes": [
+            {"id": "a", "label": "dup", "file_type": "code", "source_file": "a.py"},
+            {"id": "b", "label": "dup", "file_type": "code", "source_file": "b.py"},
+            {"id": "c", "label": "dup_1", "file_type": "code", "source_file": "c.py"},
+        ],
+        "edges": [],
+    })
+    communities = cluster(G)
+    with tempfile.TemporaryDirectory() as tmp:
+        to_obsidian(G, communities, tmp)
+        notes = [p for p in Path(tmp).rglob("*.md") if not p.name.startswith("_COMMUNITY")]
+        assert len(notes) == 3, [p.name for p in notes]
+        assert len({p.stem.lower() for p in notes}) == 3, [p.name for p in notes]
+
+
+def test_to_canvas_case_only_distinct_labels_get_distinct_files():
+    """Canvas file-node references for case-only-distinct labels must be distinct
+    case-insensitively, else both cards point at one overwritten note."""
+    G = _case_collision_graph()
+    communities = cluster(G)
+    with tempfile.TemporaryDirectory() as tmp:
+        out = Path(tmp) / "graph.canvas"
+        to_canvas(G, communities, str(out))
+        data = json.loads(out.read_text())
+        files = [n["file"] for n in data["nodes"] if n.get("type") == "file"]
+        lowered = [f.lower() for f in files]
+        assert len(set(lowered)) == len(lowered), files
+
+
+def test_obsidian_canvas_filenames_agree():
+    """The CLI calls to_obsidian and to_canvas separately with no shared map, so
+    they must independently produce the same node->filename mapping - otherwise a
+    canvas card points at a note file that doesn't exist on disk."""
+    G = _case_collision_graph()
+    communities = cluster(G)
+    with tempfile.TemporaryDirectory() as tmp:
+        to_obsidian(G, communities, tmp)
+        note_stems = {p.stem for p in Path(tmp).rglob("*.md") if not p.name.startswith("_COMMUNITY")}
+        out = Path(tmp) / "graph.canvas"
+        to_canvas(G, communities, str(out))
+        data = json.loads(out.read_text())
+        canvas_stems = {Path(n["file"]).stem for n in data["nodes"] if n.get("type") == "file"}
+        assert canvas_stems <= note_stems, (sorted(canvas_stems), sorted(note_stems))
+
+
+def test_to_obsidian_community_notes_case_collision():
+    """Two community labels differing only by case must each get their own
+    `_COMMUNITY_*.md` overview note. This path had no dedup at all, so even
+    same-case duplicate labels previously overwrote silently."""
+    G = build_from_json({
+        "nodes": [
+            {"id": "n1", "label": "alpha", "file_type": "code", "source_file": "a.py"},
+            {"id": "n2", "label": "beta", "file_type": "code", "source_file": "b.py"},
+        ],
+        "edges": [],
+    })
+    communities = {0: ["n1"], 1: ["n2"]}
+    labels = {0: "API", 1: "Api"}
+    with tempfile.TemporaryDirectory() as tmp:
+        to_obsidian(G, communities, tmp, community_labels=labels)
+        comm = [p for p in Path(tmp).rglob("_COMMUNITY_*.md")]
+        assert len(comm) == 2, [p.name for p in comm]
+        lowered = [p.stem.lower() for p in comm]
+        assert len(set(lowered)) == len(lowered), [p.name for p in comm]
+
+
 # ── Issue #834: backup_if_protected ──────────────────────────────────────────
 
 def test_backup_no_graph_json(tmp_path):
diff --git a/tests/test_wiki.py b/tests/test_wiki.py
index 063d47ed..b4fc97cd 100644
--- a/tests/test_wiki.py
+++ b/tests/test_wiki.py
@@ -210,3 +210,41 @@ def test_community_article_handles_null_source_file(tmp_path):
     # Must not raise TypeError
     to_wiki(G, communities, tmp_path, community_labels=labels)
     assert (tmp_path / "index.md").exists()
+
+
+def test_to_wiki_case_only_distinct_labels_dont_overwrite(tmp_path):
+    """Two community labels differing only by case must each get their own
+    article. The slug-dedup set folds case, so on case-insensitive filesystems
+    (macOS/APFS, Windows/NTFS) the second article gets a numeric suffix instead
+    of silently overwriting the first."""
+    G = nx.Graph()
+    G.add_node("n1", label="parse", file_type="code", source_file="a.py", community=0)
+    G.add_node("n2", label="render", file_type="code", source_file="b.py", community=1)
+    G.add_edge("n1", "n2", relation="calls", confidence="EXTRACTED", weight=1.0)
+    communities = {0: ["n1"], 1: ["n2"]}
+    labels = {0: "Parser", 1: "parser"}
+    n = to_wiki(G, communities, tmp_path, community_labels=labels)
+    articles = [p for p in tmp_path.glob("*.md") if p.name != "index.md"]
+    # both communities survive as separate files on disk (no silent overwrite)
+    assert len(articles) == n == 2, [p.name for p in articles]
+    # filenames are distinct even when compared case-insensitively
+    lowered = [p.stem.lower() for p in articles]
+    assert len(set(lowered)) == len(lowered), [p.name for p in articles]
+
+
+def test_to_wiki_god_node_label_case_collides_with_community(tmp_path):
+    """Community and god-node articles share one slug-dedup set, so a god-node
+    label differing only by case from a community label must still get its own
+    file rather than overwriting the community article."""
+    G = nx.Graph()
+    G.add_node("n1", label="parse", file_type="code", source_file="a.py", community=0)
+    G.add_node("n2", label="run", file_type="code", source_file="b.py", community=0)
+    G.add_edge("n1", "n2", relation="calls", confidence="EXTRACTED", weight=1.0)
+    communities = {0: ["n1", "n2"]}
+    labels = {0: "Parser"}
+    god_nodes = [{"id": "n1", "label": "parser", "degree": 1}]
+    n = to_wiki(G, communities, tmp_path, community_labels=labels, god_nodes_data=god_nodes)
+    articles = [p for p in tmp_path.glob("*.md") if p.name != "index.md"]
+    assert len(articles) == n == 2, [p.name for p in articles]
+    lowered = [p.stem.lower() for p in articles]
+    assert len(set(lowered)) == len(lowered), [p.name for p in articles]