allozaur/feat/chat form contenteditable (#26717)

* feat: Add contenteditable tokenizer for badge/code-chip chat input

* feat: Add source-space undo/redo history for the rich input

* feat: Split text glued to a closing code fence onto its own line

* feat: Add ChatFormContenteditable rich input renderer

* feat : wire the contenteditable into ChatForm with auto-switch gating

tools/ui/tests/unit/source-history.test.ts

@@ -0,0 +1,65 @@
+import { describe, expect, it } from 'vitest';
+import { SourceHistory } from '$lib/utils';
+
+describe('SourceHistory', () => {
+	it('coalesces pushes inside the group window into one undo step', () => {
+		const h = new SourceHistory(100, 800);
+		h.push({ value: '', caret: 0 }, 1000);
+		h.push({ value: 'a', caret: 1 }, 1200);
+		h.push({ value: 'ab', caret: 2 }, 1500);
+
+		expect(h.undo({ value: 'abc', caret: 3 })).toEqual({ value: '', caret: 0 });
+		expect(h.undo({ value: '', caret: 0 })).toBeNull();
+	});
+
+	it('starts a new group once the window has passed', () => {
+		const h = new SourceHistory(100, 800);
+		h.push({ value: '', caret: 0 }, 1000);
+		h.push({ value: 'abc', caret: 3 }, 2000);
+
+		expect(h.undo({ value: 'abcdef', caret: 6 })).toEqual({ value: 'abc', caret: 3 });
+		expect(h.undo({ value: 'abc', caret: 3 })).toEqual({ value: '', caret: 0 });
+	});
+
+	it('newGroup forces a separate entry even inside the window', () => {
+		const h = new SourceHistory(100, 800);
+		h.push({ value: '', caret: 0 }, 1000);
+		h.push({ value: 'abc', caret: 3 }, 1100, true);
+
+		expect(h.undo({ value: 'abc\n', caret: 4 })).toEqual({ value: 'abc', caret: 3 });
+		expect(h.undo({ value: 'abc', caret: 3 })).toEqual({ value: '', caret: 0 });
+	});
+
+	it('redo round-trips and a fresh push clears the redo stack', () => {
+		const h = new SourceHistory(100, 800);
+		h.push({ value: '', caret: 0 }, 1000);
+
+		const undone = h.undo({ value: 'abc', caret: 3 });
+		expect(undone).toEqual({ value: '', caret: 0 });
+		expect(h.redo({ value: '', caret: 0 })).toEqual({ value: 'abc', caret: 3 });
+
+		h.undo({ value: 'abc', caret: 3 });
+		h.push({ value: '', caret: 0 }, 5000);
+		expect(h.redo({ value: 'x', caret: 1 })).toBeNull();
+	});
+
+	it('starts a new group on the first edit after an undo', () => {
+		const h = new SourceHistory(100, 800);
+		h.push({ value: '', caret: 0 }, 1000);
+		h.undo({ value: 'abc', caret: 3 });
+
+		h.push({ value: '', caret: 0 }, 1200);
+		expect(h.undo({ value: 'x', caret: 1 })).toEqual({ value: '', caret: 0 });
+	});
+
+	it('evicts the oldest entry past the limit', () => {
+		const h = new SourceHistory(2, 800);
+		h.push({ value: 'one', caret: 0 }, 1000);
+		h.push({ value: 'two', caret: 0 }, 2000);
+		h.push({ value: 'three', caret: 0 }, 3000);
+
+		expect(h.undo({ value: 'cur', caret: 0 })).toEqual({ value: 'three', caret: 0 });
+		expect(h.undo({ value: 'three', caret: 0 })).toEqual({ value: 'two', caret: 0 });
+		expect(h.undo({ value: 'two', caret: 0 })).toBeNull();
+	});
+});