refactor: centralize font-size clamps in textLimits.ts

Single source of truth for font-size constraints (text 6–160, sticky
8–96) used by creation defaults, resize-bake, and any future mutation
paths. Replaces scattered hardcoded min/max values.

frontend/src/canvas/textLimits.ts

@@ -0,0 +1,23 @@
+/**
+ * textLimits — single source of truth for font-size constraints.
+ *
+ * Every path that creates, resizes, or mutates fontSize on text/sticky
+ * items must go through these helpers. This prevents inconsistent
+ * clamping when ranges are widened later.
+ */
+
+// Plain text: generous range for direct manipulation
+const TEXT_FONT_MIN = 6;
+const TEXT_FONT_MAX = 160;
+
+// Sticky note text: narrower range (card layout breaks at extremes)
+const STICKY_FONT_MIN = 8;
+const STICKY_FONT_MAX = 96;
+
+export function clampTextFontSize(size: number): number {
+  return Math.round(Math.min(TEXT_FONT_MAX, Math.max(TEXT_FONT_MIN, size)));
+}
+
+export function clampStickyFontSize(size: number): number {
+  return Math.round(Math.min(STICKY_FONT_MAX, Math.max(STICKY_FONT_MIN, size)));
+}

frontend/src/canvas/tools.ts

@@ -13,6 +13,7 @@ import type { SelectionManager } from './SelectionManager';
 import { DrawingSprite } from './sprites/DrawingSprite';
 import type { DrawingObject } from './scene-format';
 import { TextEditor } from './TextEditor';
+import { clampTextFontSize, clampStickyFontSize } from './textLimits';
 
 export enum ToolType {
   SELECT = 'SELECT',
@@ -117,7 +118,7 @@ export function activateTool(
           name: '',
           visible: true,
           text: ' ', // placeholder — will be replaced by user input
-          fontSize: screenToWorld(DEFAULT_TEXT_SCREEN_FONT, zoom, 10, 72),
+          fontSize: clampTextFontSize(screenToWorld(DEFAULT_TEXT_SCREEN_FONT, zoom, 6, 160)),
           fill: opts.color!,
           fontFamily: 'sans-serif',
         };
@@ -344,7 +345,7 @@ export function activateTool(
           name: '',
           visible: true,
           text: '',
-          fontSize: screenToWorld(DEFAULT_STICKY_SCREEN_FONT, zoom, 10, 48),
+          fontSize: clampStickyFontSize(screenToWorld(DEFAULT_STICKY_SCREEN_FONT, zoom, 8, 96)),
           fontFamily: 'Inter, system-ui, sans-serif',
           fill: '#ffd43b',     // default yellow
           textColor: '#1a1a1a',

frontend/src/hooks/useCanvasSetup.ts

@@ -15,6 +15,7 @@ import { PinOverlay } from '../canvas/PinOverlay';
 import { CropOverlay } from '../canvas/CropOverlay';
 import { TextSprite } from '../canvas/sprites/TextSprite';
 import { TextSharpnessManager } from '../canvas/textSharpness';
+import { clampTextFontSize } from '../canvas/textLimits';
 // PresenceOverlay removed — remote selection highlighting was too heavy for minimal benefit
 import { connectSocket, disconnectSocket } from '../socket';
 import api from '../api';
@@ -218,7 +219,7 @@ export function useCanvasSetup(deps: CanvasSetupDeps) {
             // Use average scale as font multiplier
             const scale = (absSx + absSy) / 2;
             const d = item.data as any;
-            d.fontSize = Math.round(d.fontSize * scale);
+            d.fontSize = clampTextFontSize(d.fontSize * scale);
             d.sx = item.data.sx > 0 ? 1 : -1;
             d.sy = item.data.sy > 0 ? 1 : -1;
             if (item.displayObject instanceof TextSprite) {