diff --git a/internal/schemavalidators/internal_schemas/aicodingsession/ai-coding-session-0.1.schema.json b/internal/schemavalidators/internal_schemas/aicodingsession/ai-coding-session-0.1.schema.json
index 75d5a4e43..fbfaf42ad 100644
--- a/internal/schemavalidators/internal_schemas/aicodingsession/ai-coding-session-0.1.schema.json
+++ b/internal/schemavalidators/internal_schemas/aicodingsession/ai-coding-session-0.1.schema.json
@@ -233,6 +233,10 @@
                     "end": {
                       "type": "integer",
                       "description": "End line number"
+                    },
+                    "attribution": {
+                      "type": "string",
+                      "description": "Owner of the lines in the range: ai or human. A range with an attribution is a position in the file at the pushed commit. A range with no attribution is an AI range at edit time."
                     }
                   },
                   "additionalProperties": false
diff --git a/internal/schemavalidators/schemavalidators_test.go b/internal/schemavalidators/schemavalidators_test.go
index 5bf0a51d2..ba2c15bb3 100644
--- a/internal/schemavalidators/schemavalidators_test.go
+++ b/internal/schemavalidators/schemavalidators_test.go
@@ -445,6 +445,56 @@ func TestValidateAICodingSessionSpec(t *testing.T) {
 	}
 }
 
+// TestValidateAICodingSessionLineRanges covers code_changes.files[].line_ranges.
+// A range can say if its lines are AI or human (spec issue-3639, line ranges
+// D-005). A range with no attribution keeps its earlier meaning, so the
+// property is optional.
+func TestValidateAICodingSessionLineRanges(t *testing.T) {
+	withRange := func(t *testing.T, r map[string]any) map[string]any {
+		t.Helper()
+		f, err := os.ReadFile("./testdata/ai_coding_session_valid.json")
+		require.NoError(t, err)
+
+		var payload map[string]any
+		require.NoError(t, json.Unmarshal(f, &payload))
+		payload["code_changes"] = map[string]any{
+			"files": []any{
+				map[string]any{"path": "main.go", "status": "modified", "line_ranges": []any{r}},
+			},
+		}
+		return payload
+	}
+
+	const (
+		keyStart       = "start"
+		keyEnd         = "end"
+		keyAttribution = "attribution"
+	)
+
+	testCases := []struct {
+		name    string
+		r       map[string]any
+		wantErr bool
+	}{
+		{name: "accepts a range with no attribution", r: map[string]any{keyStart: 1, keyEnd: 3}},
+		{name: "accepts an AI range", r: map[string]any{keyStart: 1, keyEnd: 3, keyAttribution: "ai"}},
+		{name: "accepts a human range", r: map[string]any{keyStart: 4, keyEnd: 4, keyAttribution: "human"}},
+		{name: "rejects a non-string attribution", r: map[string]any{keyStart: 1, keyEnd: 3, keyAttribution: 1}, wantErr: true},
+		{name: "rejects an unknown property", r: map[string]any{keyStart: 1, keyEnd: 3, "owner": "ai"}, wantErr: true},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := schemavalidators.ValidateAICodingSession(withRange(t, tc.r), "")
+			if tc.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+		})
+	}
+}
+
 func TestValidateSecurityContext(t *testing.T) {
 	testCases := []struct {
 		name     string
diff --git a/pkg/attestation/crafter/materials/aicodingsession/aicodingsession.go b/pkg/attestation/crafter/materials/aicodingsession/aicodingsession.go
index 706b071ef..fbe4a7ae7 100644
--- a/pkg/attestation/crafter/materials/aicodingsession/aicodingsession.go
+++ b/pkg/attestation/crafter/materials/aicodingsession/aicodingsession.go
@@ -222,6 +222,10 @@ type GitContext struct {
 type LineRange struct {
 	Start int `json:"start"`
 	End   int `json:"end"`
+	// Attribution is the owner of the lines, ai or human. A range with an
+	// attribution is a position in the file at the pushed commit. A range
+	// with no attribution is an AI range at edit time, as older CLIs write it.
+	Attribution string `json:"attribution,omitempty"`
 }
 
 // FileChange represents a single file modification in the session.