feat(zpl): emit partial ^CF for round-trip fidelity

The ^CF parameters are individually optional per Zebra spec: ^CF0 sets
the font without changing the height, ^CF,30 sets the height without
changing the font. Previously the generator required both fields and
would silently drop a partial command on round-trip. Now emits whichever
fields are set, with explicit round-trip tests for both partial forms.

Author: u8array

src/lib/zplGenerator.test.ts

@@ -96,14 +96,19 @@ describe('generateZPL — printer params', () => {
     expect(zpl).toContain('^CF0,30');
   });
 
-  it('omits ^CF when defaultFontId is set without defaultFontHeight', () => {
-    expect(generateZPL({ ...BASE_LABEL, defaultFontId: '0' }, []))
-      .not.toContain('^CF');
+  it('emits ^CF{id} when only defaultFontId is set', () => {
+    const zpl = generateZPL({ ...BASE_LABEL, defaultFontId: '0' }, []);
+    expect(zpl).toContain('^CF0');
+    expect(zpl).not.toContain('^CF0,');
   });
 
-  it('omits ^CF when defaultFontHeight is set without defaultFontId', () => {
+  it('emits ^CF,{height} when only defaultFontHeight is set', () => {
     expect(generateZPL({ ...BASE_LABEL, defaultFontHeight: 30 }, []))
-      .not.toContain('^CF');
+      .toContain('^CF,30');
+  });
+
+  it('omits ^CF when neither defaultFont field is set', () => {
+    expect(generateZPL(BASE_LABEL, [])).not.toContain('^CF');
   });
 
   it('emits printer params in canonical header order before ^LS', () => {
@@ -238,4 +243,18 @@ describe('generateZPL — parse/generate roundtrip', () => {
     expect(labelConfig.defaultFontId).toBe('0');
     expect(labelConfig.defaultFontHeight).toBe(30);
   });
+
+  it('preserves partial ^CF (id only) through generate -> parse', () => {
+    const regenerated = generateZPL({ ...BASE_LABEL, defaultFontId: 'A' }, []);
+    const { labelConfig } = parseZPL(regenerated, BASE_LABEL.dpmm);
+    expect(labelConfig.defaultFontId).toBe('A');
+    expect(labelConfig.defaultFontHeight).toBeUndefined();
+  });
+
+  it('preserves partial ^CF (height only) through generate -> parse', () => {
+    const regenerated = generateZPL({ ...BASE_LABEL, defaultFontHeight: 25 }, []);
+    const { labelConfig } = parseZPL(regenerated, BASE_LABEL.dpmm);
+    expect(labelConfig.defaultFontId).toBeUndefined();
+    expect(labelConfig.defaultFontHeight).toBe(25);
+  });
 });

src/lib/zplGenerator.ts

@@ -30,8 +30,14 @@ export function generateZPL(label: LabelConfig, objects: LabelObject[]): string
   // darkness=0 is a valid value (printer baseline), so check undefined explicitly.
   if (label.darkness !== undefined) lines.push(`^MD${label.darkness}`);
   if (label.printOrientation) lines.push(`^PO${label.printOrientation}`);
-  if (label.defaultFontId && label.defaultFontHeight !== undefined) {
-    lines.push(`^CF${label.defaultFontId},${label.defaultFontHeight}`);
+  // ^CF parameters are individually optional per Zebra spec: ^CF0 sets the
+  // font only, ^CF,30 sets the height only. Preserves round-trip fidelity
+  // when an imported label used a partial command.
+  if (label.defaultFontId || label.defaultFontHeight !== undefined) {
+    const id = label.defaultFontId ?? "";
+    const height =
+      label.defaultFontHeight !== undefined ? `,${label.defaultFontHeight}` : "";
+    lines.push(`^CF${id}${height}`);
   }
   if (label.labelShift) lines.push(`^LS${label.labelShift}`);