fix(core): include full color value in getStyleLine hash to prevent collision

packages/core/src/terminal/Screen.test.ts

@@ -133,6 +133,91 @@ describe('Screen', () => {
     });
 });
 
+describe('getStyleLine', () => {
+    it('returns empty string for out-of-bounds row', () => {
+        const screen = new Screen(5, 3);
+        expect(screen.getStyleLine(-1)).toBe('');
+        expect(screen.getStyleLine(3)).toBe('');
+    });
+
+    it('different ansi256 codes produce different hashes', () => {
+        const screen = new Screen(5, 1);
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'ansi256', code: 1 } });
+        const hash1 = screen.getStyleLine(0);
+
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'ansi256', code: 9 } });
+        const hash2 = screen.getStyleLine(0);
+
+        expect(hash1).not.toBe(hash2);
+    });
+
+    it('different named colors produce different hashes', () => {
+        const screen = new Screen(5, 1);
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'named', name: 'red' } });
+        const hash1 = screen.getStyleLine(0);
+
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'named', name: 'blue' } });
+        const hash2 = screen.getStyleLine(0);
+
+        expect(hash1).not.toBe(hash2);
+    });
+
+    it('different rgb values produce different hashes', () => {
+        const screen = new Screen(5, 1);
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'rgb', r: 255, g: 0, b: 0 } });
+        const hash1 = screen.getStyleLine(0);
+
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'rgb', r: 0, g: 255, b: 0 } });
+        const hash2 = screen.getStyleLine(0);
+
+        expect(hash1).not.toBe(hash2);
+    });
+
+    it('different hex values produce different hashes', () => {
+        const screen = new Screen(5, 1);
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'hex', hex: '#ff0000' } });
+        const hash1 = screen.getStyleLine(0);
+
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'hex', hex: '#00ff00' } });
+        const hash2 = screen.getStyleLine(0);
+
+        expect(hash1).not.toBe(hash2);
+    });
+
+    it('same color values produce the same hash', () => {
+        const screen = new Screen(5, 1);
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'ansi256', code: 42 } });
+        const hash1 = screen.getStyleLine(0);
+
+        screen.setCell(0, 0, { char: 'A', fg: { type: 'ansi256', code: 42 } });
+        const hash2 = screen.getStyleLine(0);
+
+        expect(hash1).toBe(hash2);
+    });
+
+    it('style flags still affect the hash', () => {
+        const screen = new Screen(5, 1);
+        screen.setCell(0, 0, { char: 'A', bold: false });
+        const hash1 = screen.getStyleLine(0);
+
+        screen.setCell(0, 0, { char: 'A', bold: true });
+        const hash2 = screen.getStyleLine(0);
+
+        expect(hash1).not.toBe(hash2);
+    });
+
+    it('background color changes are detected', () => {
+        const screen = new Screen(5, 1);
+        screen.setCell(0, 0, { char: 'A', bg: { type: 'ansi256', code: 1 } });
+        const hash1 = screen.getStyleLine(0);
+
+        screen.setCell(0, 0, { char: 'A', bg: { type: 'ansi256', code: 9 } });
+        const hash2 = screen.getStyleLine(0);
+
+        expect(hash1).not.toBe(hash2);
+    });
+});
+
 describe('cellsEqual', () => {
     it('returns true for identical cells', () => {
         const a = emptyCell();

packages/core/src/terminal/Screen.ts

@@ -7,6 +7,32 @@ import { stringWidth, segmenter } from '../utils/unicode.js';
 import { stripAnsiControl } from '../utils/ansi.js';
 import { caps } from './env-caps.js';
 
+/**
+ * Produce a numeric fingerprint from a Color value.
+ * The hash incorporates both the color type and its specific value
+ * (code, name, r/g/b, or hex) so that two colors of the same type
+ * but different values produce distinct hashes.
+ */
+function hashColor(c: Color): number {
+    switch (c.type) {
+        case 'none':
+            return 0;
+        case 'named':
+            return c.name.charCodeAt(0) * 31 + c.name.charCodeAt(c.name.length - 1);
+        case 'ansi256':
+            return c.code * 7 + 1;
+        case 'rgb':
+            return (c.r << 16) | (c.g << 8) | c.b;
+        case 'hex': {
+            let h = 0;
+            for (let i = 0; i < c.hex.length; i++) {
+                h = ((h << 5) - h + c.hex.charCodeAt(i)) | 0;
+            }
+            return h;
+        }
+    }
+}
+
 const EMPTY_COLOR: Color = Object.freeze({ type: 'none' } as const);
 
 /**
@@ -194,16 +220,16 @@ export class Screen {
         let hash = 0;
         for (const cell of this.back[row]) {
             if (cell.width === 0) continue;
-            const fg = cell.fg.type;
-            const bg = cell.bg.type;
+            const fgVal = hashColor(cell.fg);
+            const bgVal = hashColor(cell.bg);
             const bits =
                 (cell.bold ? 1 : 0) |
                 (cell.italic ? 2 : 0) |
                 (cell.underline ? 4 : 0) |
                 (cell.dim ? 8 : 0) |
                 (cell.strikethrough ? 16 : 0) |
                 (cell.inverse ? 32 : 0);
-            const seed = fg.charCodeAt(0) * 65536 + bg.charCodeAt(0) * 4096 + bits;
+            const seed = fgVal * 65536 + bgVal * 4096 + bits;
             hash = ((hash << 7) - hash + seed) | 0;
             if (cell.link) {
                 for (let i = 0; i < cell.link.length; i++)