diff --git a/src/persistence/mod.rs b/src/persistence/mod.rs
index 4052e29..f3cd25e 100644
--- a/src/persistence/mod.rs
+++ b/src/persistence/mod.rs
@@ -803,4 +803,265 @@ mod tests {
         let m2: Model = serde_json::from_str(&json).unwrap();
         assert_eq!(m2.name, "Budget");
     }
+
+    // ── save/load roundtrip via file ────────────────────────────────────
+
+    #[test]
+    fn save_and_load_roundtrip_plain() {
+        let mut m = two_cat_model();
+        m.set_cell(
+            coord(&[("Type", "Food"), ("Month", "Jan")]),
+            CellValue::Number(42.0),
+        );
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("test.improv");
+        super::save(&m, &path).unwrap();
+        let loaded = super::load(&path).unwrap();
+        assert_eq!(loaded.name, "Budget");
+        assert_eq!(
+            loaded.get_cell(&coord(&[("Type", "Food"), ("Month", "Jan")])),
+            Some(&CellValue::Number(42.0))
+        );
+    }
+
+    #[test]
+    fn save_and_load_roundtrip_gzip() {
+        let mut m = two_cat_model();
+        m.set_cell(
+            coord(&[("Type", "Gas"), ("Month", "Feb")]),
+            CellValue::Number(99.0),
+        );
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("test.improv.gz");
+        super::save(&m, &path).unwrap();
+        let loaded = super::load(&path).unwrap();
+        assert_eq!(loaded.name, "Budget");
+        assert_eq!(
+            loaded.get_cell(&coord(&[("Type", "Gas"), ("Month", "Feb")])),
+            Some(&CellValue::Number(99.0))
+        );
+    }
+
+    // ── autosave_path ───────────────────────────────────────────────────
+
+    #[test]
+    fn autosave_path_inserts_dot_prefix() {
+        let p = std::path::Path::new("/home/user/data/budget.improv");
+        let auto = super::autosave_path(p);
+        assert_eq!(auto.file_name().unwrap().to_str().unwrap(), ".budget.improv.autosave");
+    }
+
+    // ── format_md: collapsed groups ─────────────────────────────────────
+
+    #[test]
+    fn format_md_collapsed_group() {
+        let mut m = two_cat_model();
+        m.active_view_mut()
+            .toggle_group_collapse("Type", "MyGroup");
+        let text = format_md(&m);
+        assert!(text.contains("collapsed: Type/MyGroup"));
+    }
+
+    // ── format_md: page axis without selection ──────────────────────────
+
+    #[test]
+    fn format_md_page_without_selection() {
+        let mut m = two_cat_model();
+        m.active_view_mut().set_axis("Month", Axis::Page);
+        // Don't set a page selection
+        let text = format_md(&m);
+        assert!(text.contains("Month: page"));
+        // Should NOT have a comma after "page" (no selection)
+        let line = text.lines().find(|l| l.starts_with("Month:")).unwrap();
+        assert!(!line.contains(','), "Expected no selection, got: {line}");
+    }
+
+    // ── format_md: none axis ────────────────────────────────────────────
+
+    #[test]
+    fn format_md_none_axis() {
+        let mut m = two_cat_model();
+        m.active_view_mut().set_axis("Month", Axis::None);
+        let text = format_md(&m);
+        assert!(text.contains("Month: none"));
+    }
+
+    // ── format_md: number format ────────────────────────────────────────
+
+    #[test]
+    fn format_md_includes_number_format() {
+        let mut m = two_cat_model();
+        m.active_view_mut().number_format = ",.2f".to_string();
+        let text = format_md(&m);
+        assert!(text.contains("format: ,.2f"));
+    }
+
+    // ── parse_md: comments and blank lines ──────────────────────────────
+
+    #[test]
+    fn parse_md_ignores_blank_and_comment_lines() {
+        let text = r#"# Test Model
+
+## Category: Type
+- Food
+- Gas
+
+## Data
+Type=Food = 42
+"#;
+        let m = parse_md(text).unwrap();
+        assert_eq!(m.name, "Test Model");
+        assert!(m.category("Type").is_some());
+    }
+
+    // ── parse_md: text values ───────────────────────────────────────────
+
+    #[test]
+    fn parse_md_round_trips_text_cell_values() {
+        let mut m = two_cat_model();
+        m.set_cell(
+            coord(&[("Type", "Food"), ("Month", "Jan")]),
+            CellValue::Text("pending".to_string()),
+        );
+        let text = format_md(&m);
+        let loaded = parse_md(&text).unwrap();
+        assert_eq!(
+            loaded.get_cell(&coord(&[("Type", "Food"), ("Month", "Jan")])),
+            Some(&CellValue::Text("pending".to_string()))
+        );
+    }
+
+    // ── parse_md: collapsed groups roundtrip ────────────────────────────
+
+    #[test]
+    fn parse_md_round_trips_collapsed_group() {
+        let mut m = two_cat_model();
+        m.active_view_mut()
+            .toggle_group_collapse("Type", "MyGroup");
+        let text = format_md(&m);
+        let loaded = parse_md(&text).unwrap();
+        assert!(loaded.active_view().is_group_collapsed("Type", "MyGroup"));
+    }
+
+    // ── parse_md: number format roundtrip ───────────────────────────────
+
+    #[test]
+    fn parse_md_round_trips_number_format() {
+        let mut m = two_cat_model();
+        m.active_view_mut().number_format = ",.2f".to_string();
+        let text = format_md(&m);
+        let loaded = parse_md(&text).unwrap();
+        assert_eq!(loaded.active_view().number_format, ",.2f");
+    }
+
+    // ── parse_md: none axis roundtrip ───────────────────────────────────
+
+    #[test]
+    fn parse_md_round_trips_none_axis() {
+        let mut m = two_cat_model();
+        m.active_view_mut().set_axis("Month", Axis::None);
+        let text = format_md(&m);
+        let loaded = parse_md(&text).unwrap();
+        assert_eq!(loaded.active_view().axis_of("Month"), Axis::None);
+    }
+
+    // ── parse_md: multiple views ────────────────────────────────────────
+
+    #[test]
+    fn parse_md_round_trips_multiple_views() {
+        let mut m = two_cat_model();
+        m.create_view("Alternate");
+        {
+            let v = m.views.get_mut("Alternate").unwrap();
+            v.set_axis("Type", Axis::Column);
+            v.set_axis("Month", Axis::Row);
+        }
+        let text = format_md(&m);
+        let loaded = parse_md(&text).unwrap();
+        assert!(loaded.views.contains_key("Default"));
+        assert!(loaded.views.contains_key("Alternate"));
+        let alt = loaded.views.get("Alternate").unwrap();
+        assert_eq!(alt.axis_of("Type"), Axis::Column);
+        assert_eq!(alt.axis_of("Month"), Axis::Row);
+    }
+
+    // ── export_csv ──────────────────────────────────────────────────────
+
+    #[test]
+    fn export_csv_produces_valid_output() {
+        let mut m = two_cat_model();
+        m.set_cell(
+            coord(&[("Type", "Food"), ("Month", "Jan")]),
+            CellValue::Number(100.0),
+        );
+        m.set_cell(
+            coord(&[("Type", "Gas"), ("Month", "Feb")]),
+            CellValue::Number(50.0),
+        );
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("export.csv");
+        super::export_csv(&m, "Default", &path).unwrap();
+        let content = std::fs::read_to_string(&path).unwrap();
+        // Should have a header and data rows
+        let lines: Vec<&str> = content.lines().collect();
+        assert!(lines.len() >= 2, "Expected header + data, got: {content}");
+        // Header should contain column labels
+        assert!(lines[0].contains(','), "Expected CSV header, got: {}", lines[0]);
+    }
+
+    #[test]
+    fn export_csv_unknown_view_returns_error() {
+        let m = two_cat_model();
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("export.csv");
+        assert!(super::export_csv(&m, "Nonexistent", &path).is_err());
+    }
+
+    // ── Full save/load/format roundtrip with all features ───────────────
+
+    #[test]
+    fn full_roundtrip_preserves_all_features() {
+        let mut m = two_cat_model();
+        // Add data
+        m.set_cell(
+            coord(&[("Type", "Food"), ("Month", "Jan")]),
+            CellValue::Number(100.0),
+        );
+        m.set_cell(
+            coord(&[("Type", "Gas"), ("Month", "Feb")]),
+            CellValue::Text("pending".to_string()),
+        );
+        // Add formula
+        let f = parse_formula("Gas = Food * 2", "Type").unwrap();
+        m.add_formula(f);
+        // Configure view
+        m.active_view_mut().set_axis("Month", Axis::Page);
+        m.active_view_mut()
+            .set_page_selection("Month", "Jan");
+        m.active_view_mut().hide_item("Type", "Gas");
+        m.active_view_mut()
+            .toggle_group_collapse("Type", "G1");
+        m.active_view_mut().number_format = ",.0".to_string();
+
+        let text = format_md(&m);
+        let loaded = parse_md(&text).unwrap();
+
+        // Verify everything roundtripped
+        assert_eq!(loaded.name, "Budget");
+        assert_eq!(
+            loaded.get_cell(&coord(&[("Type", "Food"), ("Month", "Jan")])),
+            Some(&CellValue::Number(100.0))
+        );
+        assert_eq!(
+            loaded.get_cell(&coord(&[("Type", "Gas"), ("Month", "Feb")])),
+            Some(&CellValue::Text("pending".to_string()))
+        );
+        assert!(!loaded.formulas().is_empty());
+        let v = loaded.active_view();
+        assert_eq!(v.axis_of("Month"), Axis::Page);
+        assert_eq!(v.page_selection("Month"), Some("Jan"));
+        assert!(v.is_hidden("Type", "Gas"));
+        assert!(v.is_group_collapsed("Type", "G1"));
+        assert_eq!(v.number_format, ",.0");
+    }
 }