fix: tighten project instruction path handling

packages/util/paths/tests/paths.spec.ts

@@ -0,0 +1,25 @@
+import { homedir } from 'node:os'
+import { join } from 'node:path'
+import { describe, expect, it } from 'vitest'
+import {
+  DEFAULT_DSH_HOME_DISPLAY,
+  DSH_HOME_DIR_NAME,
+  defaultDshHome,
+  expandHomePath,
+} from '@deepseek-ai/dsh-paths'
+
+describe('dsh path helpers', () => {
+  it('owns the shared default DSH home directory name', () => {
+    expect(DSH_HOME_DIR_NAME).toBe('.dsh')
+    expect(DEFAULT_DSH_HOME_DISPLAY).toBe('~/.dsh')
+    expect(defaultDshHome()).toBe(join(homedir(), '.dsh'))
+  })
+
+  it('expands tilde paths without changing non-tilde paths', () => {
+    expect(expandHomePath('~')).toBe(homedir())
+    expect(expandHomePath('~/.dsh')).toBe(join(homedir(), '.dsh'))
+    expect(expandHomePath('~\\.dsh')).toBe(join(homedir(), '.dsh'))
+    expect(expandHomePath('/tmp/.dsh')).toBe('/tmp/.dsh')
+    expect(expandHomePath('~other/.dsh')).toBe('~other/.dsh')
+  })
+})