diff --git a/ingestion/internal/graph/extract.go b/ingestion/internal/graph/extract.go
index 0281665..f557cd2 100644
--- a/ingestion/internal/graph/extract.go
+++ b/ingestion/internal/graph/extract.go
@@ -35,6 +35,12 @@ type Entity struct {
 	Wing    string // optional; from frontmatter or path
 	Hall    string // optional; from frontmatter or path
 	Title   string // optional; from frontmatter
+	// DIKW tier — infra#72. Empty until M3 migration writes `tier:`
+	// frontmatter to every entry. Path-inferred tier kicks in as a
+	// fallback so the column populates immediately on backfill even
+	// for entries that haven't had their frontmatter rewritten yet.
+	Tier  string // "inbox" | "note" | "knowledge"
+	Topic string // kebab-slug; the thing the entry is about
 }
 
 // Edge represents a directed relationship between two slugs.
@@ -67,11 +73,42 @@ func Extract(docPath string, content []byte) (Entity, []Edge, bool) {
 	ent := Entity{DocPath: docPath, Slug: slug}
 	classifyByPath(&ent, docPath)
 	readFrontmatter(&ent, content)
+	inferTierFromPath(&ent, docPath)
 
 	edges := extractEdges(docPath, slug, content)
 	return ent, edges, true
 }
 
+// inferTierFromPath fills Tier when frontmatter didn't already set it.
+// The new layout has dedicated subtrees per tier; pre-migration paths
+// (knowledge/, wiki/, raw/, sessions/) get their best-guess mapping so
+// the column populates on backfill before the M3 file moves run.
+func inferTierFromPath(e *Entity, docPath string) {
+	if e.Tier != "" {
+		return
+	}
+	parts := strings.Split(docPath, "/")
+	if len(parts) == 0 {
+		return
+	}
+	switch parts[0] {
+	case "inbox":
+		e.Tier = "inbox"
+	case "notes":
+		e.Tier = "note"
+	case "knowledge":
+		e.Tier = "knowledge"
+	case "wiki":
+		// Pre-M3 wiki layout: sources are synth output of raw inbox
+		// material (I tier); concepts + entities are reference notes
+		// (also I tier); top-level wiki/<slug>.md is unstructured
+		// reference too. None of these are reusable lessons (K).
+		e.Tier = "note"
+	case "raw", "sessions", "clips":
+		e.Tier = "inbox"
+	}
+}
+
 func slugFromPath(docPath string) string {
 	base := filepath.Base(docPath)
 	if !strings.HasSuffix(base, ".md") {
@@ -152,6 +189,14 @@ func readFrontmatter(e *Entity, content []byte) {
 			if e.Hall == "" {
 				e.Hall = v
 			}
+		case "tier":
+			if e.Tier == "" {
+				e.Tier = v
+			}
+		case "topic":
+			if e.Topic == "" {
+				e.Topic = v
+			}
 		}
 	}
 }
diff --git a/ingestion/internal/graph/extract_test.go b/ingestion/internal/graph/extract_test.go
index 53faa0a..74619ee 100644
--- a/ingestion/internal/graph/extract_test.go
+++ b/ingestion/internal/graph/extract_test.go
@@ -119,6 +119,51 @@ func TestExtract_WikiRootFileIsKnowledgeNotHall(t *testing.T) {
 	assert.Empty(t, ent.Hall)
 }
 
+func TestExtract_TierFromFrontmatter(t *testing.T) {
+	content := []byte(`---
+tier: knowledge
+topic: postgres-roles
+title: Least-privilege migration trap
+---
+# body
+`)
+	ent, _, ok := Extract("knowledge/some-lesson.md", content)
+	require.True(t, ok)
+	assert.Equal(t, "knowledge", ent.Tier)
+	assert.Equal(t, "postgres-roles", ent.Topic)
+}
+
+func TestExtract_TierInferredFromPath(t *testing.T) {
+	cases := []struct {
+		path string
+		want string
+	}{
+		{"knowledge/foo.md", "knowledge"},
+		{"wiki/sources/x.md", "note"},
+		{"wiki/concepts/x.md", "note"},
+		{"wiki/x.md", "note"},
+		{"inbox/clips/x.md", "inbox"},
+		{"notes/x.md", "note"},
+		{"raw/x.md", "inbox"},
+		{"sessions/x.md", "inbox"},
+	}
+	for _, tc := range cases {
+		ent, _, ok := Extract(tc.path, []byte("# x\n"))
+		require.True(t, ok, tc.path)
+		assert.Equal(t, tc.want, ent.Tier, tc.path)
+	}
+}
+
+func TestExtract_FrontmatterTierBeatsPathInference(t *testing.T) {
+	// A clip explicitly promoted via frontmatter wins over the path's
+	// inbox inference. Catches the case where a file has been moved
+	// to a new location but frontmatter hasn't been updated.
+	content := []byte("---\ntier: knowledge\n---\n# x\n")
+	ent, _, ok := Extract("inbox/clips/x.md", content)
+	require.True(t, ok)
+	assert.Equal(t, "knowledge", ent.Tier)
+}
+
 func TestExtract_WikiRootFileWithFrontmatterWingHall(t *testing.T) {
 	content := []byte(`---
 wing: homelab
diff --git a/ingestion/internal/graphstore/pg.go b/ingestion/internal/graphstore/pg.go
index fa0942b..4ace151 100644
--- a/ingestion/internal/graphstore/pg.go
+++ b/ingestion/internal/graphstore/pg.go
@@ -118,16 +118,18 @@ func (s *PGStore) UpsertEntity(ctx context.Context, e graph.Entity) error {
 		e.Type = "knowledge"
 	}
 	_, err := s.pool.Exec(ctx, `
-        INSERT INTO brain_entities (slug, type, wing, hall, doc_path, title, updated_at)
-        VALUES ($1, $2, $3, $4, $5, $6, now())
+        INSERT INTO brain_entities (slug, type, wing, hall, doc_path, title, tier, topic, updated_at)
+        VALUES ($1, $2, $3, $4, $5, $6, $7, $8, now())
         ON CONFLICT (slug) DO UPDATE
         SET type       = EXCLUDED.type,
             wing       = EXCLUDED.wing,
             hall       = EXCLUDED.hall,
             doc_path   = EXCLUDED.doc_path,
             title      = EXCLUDED.title,
+            tier       = EXCLUDED.tier,
+            topic      = EXCLUDED.topic,
             updated_at = now()
-    `, e.Slug, e.Type, e.Wing, e.Hall, e.DocPath, e.Title)
+    `, e.Slug, e.Type, e.Wing, e.Hall, e.DocPath, e.Title, e.Tier, e.Topic)
 	if err != nil {
 		return fmt.Errorf("upsert entity %q: %w", e.Slug, err)
 	}