feat(conflicts): add file overlap conflict detection (S-1 Phase 1)

Detects when 2+ agent sessions write the same file within a project.
New conflicts.svelte.ts store, shared tool-files.ts utility, dispatcher
integration, health attention scoring (SCORE_FILE_CONFLICT=70), and UI
indicators in ProjectHeader + StatusBar. 170/170 tests pass.

v2/src/lib/stores/conflicts.test.ts

@@ -0,0 +1,157 @@
+import { describe, it, expect, beforeEach, vi, afterEach } from 'vitest';
+import {
+  recordFileWrite,
+  getProjectConflicts,
+  hasConflicts,
+  getTotalConflictCount,
+  clearSessionWrites,
+  clearProjectConflicts,
+  clearAllConflicts,
+} from './conflicts.svelte';
+
+beforeEach(() => {
+  clearAllConflicts();
+});
+
+describe('conflicts store', () => {
+  describe('recordFileWrite', () => {
+    it('returns false for first write to a file', () => {
+      expect(recordFileWrite('proj-1', 'sess-a', '/src/main.ts')).toBe(false);
+    });
+
+    it('returns false for same session writing same file again', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/main.ts');
+      expect(recordFileWrite('proj-1', 'sess-a', '/src/main.ts')).toBe(false);
+    });
+
+    it('returns true when a second session writes same file (new conflict)', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/main.ts');
+      expect(recordFileWrite('proj-1', 'sess-b', '/src/main.ts')).toBe(true);
+    });
+
+    it('returns false when third session writes already-conflicted file', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/main.ts');
+      recordFileWrite('proj-1', 'sess-b', '/src/main.ts');
+      expect(recordFileWrite('proj-1', 'sess-c', '/src/main.ts')).toBe(false);
+    });
+
+    it('tracks writes per project independently', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/main.ts');
+      expect(recordFileWrite('proj-2', 'sess-b', '/src/main.ts')).toBe(false);
+    });
+  });
+
+  describe('getProjectConflicts', () => {
+    it('returns empty for unknown project', () => {
+      const result = getProjectConflicts('nonexistent');
+      expect(result.conflicts).toEqual([]);
+      expect(result.conflictCount).toBe(0);
+    });
+
+    it('returns empty when no overlapping writes', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/a.ts');
+      recordFileWrite('proj-1', 'sess-b', '/src/b.ts');
+      const result = getProjectConflicts('proj-1');
+      expect(result.conflicts).toEqual([]);
+      expect(result.conflictCount).toBe(0);
+    });
+
+    it('returns conflict when two sessions write same file', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/main.ts');
+      recordFileWrite('proj-1', 'sess-b', '/src/main.ts');
+      const result = getProjectConflicts('proj-1');
+      expect(result.conflictCount).toBe(1);
+      expect(result.conflicts[0].filePath).toBe('/src/main.ts');
+      expect(result.conflicts[0].shortName).toBe('main.ts');
+      expect(result.conflicts[0].sessionIds).toContain('sess-a');
+      expect(result.conflicts[0].sessionIds).toContain('sess-b');
+    });
+
+    it('returns multiple conflicts sorted by recency', () => {
+      vi.useFakeTimers();
+      vi.setSystemTime(1000);
+      recordFileWrite('proj-1', 'sess-a', '/src/old.ts');
+      recordFileWrite('proj-1', 'sess-b', '/src/old.ts');
+      vi.setSystemTime(2000);
+      recordFileWrite('proj-1', 'sess-a', '/src/new.ts');
+      recordFileWrite('proj-1', 'sess-b', '/src/new.ts');
+      const result = getProjectConflicts('proj-1');
+      expect(result.conflictCount).toBe(2);
+      // Most recent first
+      expect(result.conflicts[0].filePath).toBe('/src/new.ts');
+      vi.useRealTimers();
+    });
+  });
+
+  describe('hasConflicts', () => {
+    it('returns false for unknown project', () => {
+      expect(hasConflicts('nonexistent')).toBe(false);
+    });
+
+    it('returns false with no overlapping writes', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/a.ts');
+      expect(hasConflicts('proj-1')).toBe(false);
+    });
+
+    it('returns true with overlapping writes', () => {
+      recordFileWrite('proj-1', 'sess-a', '/src/a.ts');
+      recordFileWrite('proj-1', 'sess-b', '/src/a.ts');
+      expect(hasConflicts('proj-1')).toBe(true);
+    });
+  });
+
+  describe('getTotalConflictCount', () => {
+    it('returns 0 with no conflicts', () => {
+      expect(getTotalConflictCount()).toBe(0);
+    });
+
+    it('counts conflicts across projects', () => {
+      recordFileWrite('proj-1', 'sess-a', '/a.ts');
+      recordFileWrite('proj-1', 'sess-b', '/a.ts');
+      recordFileWrite('proj-2', 'sess-c', '/b.ts');
+      recordFileWrite('proj-2', 'sess-d', '/b.ts');
+      expect(getTotalConflictCount()).toBe(2);
+    });
+  });
+
+  describe('clearSessionWrites', () => {
+    it('removes session from file write tracking', () => {
+      recordFileWrite('proj-1', 'sess-a', '/a.ts');
+      recordFileWrite('proj-1', 'sess-b', '/a.ts');
+      expect(hasConflicts('proj-1')).toBe(true);
+      clearSessionWrites('proj-1', 'sess-b');
+      expect(hasConflicts('proj-1')).toBe(false);
+    });
+
+    it('cleans up empty entries', () => {
+      recordFileWrite('proj-1', 'sess-a', '/a.ts');
+      clearSessionWrites('proj-1', 'sess-a');
+      expect(getProjectConflicts('proj-1').conflictCount).toBe(0);
+    });
+
+    it('no-ops for unknown project', () => {
+      clearSessionWrites('nonexistent', 'sess-a'); // Should not throw
+    });
+  });
+
+  describe('clearProjectConflicts', () => {
+    it('clears all tracking for a project', () => {
+      recordFileWrite('proj-1', 'sess-a', '/a.ts');
+      recordFileWrite('proj-1', 'sess-b', '/a.ts');
+      clearProjectConflicts('proj-1');
+      expect(hasConflicts('proj-1')).toBe(false);
+      expect(getTotalConflictCount()).toBe(0);
+    });
+  });
+
+  describe('clearAllConflicts', () => {
+    it('clears everything', () => {
+      recordFileWrite('proj-1', 'sess-a', '/a.ts');
+      recordFileWrite('proj-1', 'sess-b', '/a.ts');
+      recordFileWrite('proj-2', 'sess-c', '/b.ts');
+      recordFileWrite('proj-2', 'sess-d', '/b.ts');
+      clearAllConflicts();
+      expect(getTotalConflictCount()).toBe(0);
+    });
+  });
+});