fix(import): 媒体工厂守卫与加固——manifest 形态/侧车门控/冲突约束名/窗口边界与冲突测试

评审加固五项：
- manifest 形态守卫：bundle 在场而 metadata.manifest 非数组 → throw（与
  storageRoot 守卫同风格），不与"bundle 合法缺席=空清单"共用静默空 coercion
- 侧车门控：空清单下级②不可达，跳过侧车加载——破损侧车副本不因无用输入
  让整 job 失败
- public_path 冲突 catch 按约束名精确认领（postgres.js 的 constraint_name，
  drizzle 包一层在 cause）——未来加第三唯一索引不误标，其余 23505 原样上抛
- 集成用例：不同 source_url 同旧 uploads 路径 → 后到不覆盖、issue 报告、
  只留一行（mediaRegistered=1）
- 单测边界对拍：'<svg' 恰好收在 1024 字节窗口内（起点 1020）检出；起点
  1021 被截断为 '<sv' → null

310 测试（308+2）；typecheck/lint 三绿。

Co-Authored-By: Claude Code <noreply@anthropic.com>

tests/integration/import-media.test.ts

@@ -564,6 +564,62 @@ describe('媒体登记写入器（三级对拍 + 魔数/隔离）', () => {
     })
   })
 
+  it('public_path 唯一键冲突：不同 source_url 同旧 uploads 路径 → 后到不覆盖、issue 报告、只留一行', async () => {
+    await withTestDb(async (db) => {
+      const work = await mkdtemp(join(tmpdir(), 'sf-media-pconf-'))
+      try {
+        const dup = pngBytes(`dup-${rand()}`)
+        await mkdir(join(work, '2026/10'), { recursive: true })
+        await writeFile(join(work, '2026/10/dup.png'), dup)
+        const manifest = [manifestEntryOf('2026/10/dup.png', dup)]
+        // 两 attachment：不同源 URL（不同 host 的 uploads 域）、同一旧 uploads 相对路径
+        // → 级①命中同一清单实体 → public_path 相同 → 第二行撞 media_assets_public_path_uq
+        const events: AdapterEvent[] = [
+          attachmentEvent({ sourceId: '971', url: 'https://fixture.example/wp-content/uploads/2026/10/dup.png' }),
+          attachmentEvent({ sourceId: '972', url: 'https://mirror.example/wp-content/uploads/2026/10/dup.png' }),
+        ]
+        const { key, reg, wxr } = await registerMini(db, work)
+        try {
+          const result = await createImportJob(db, {
+            siteKey: key,
+            snapshotId: wxr.id,
+            reportRoot: join(work, 'artifacts', 'import'),
+            events: eventsOf(events),
+            pipeline: directMediaPipeline({ storageRoot: work, manifest, sidecar: [] }),
+          })
+          expect(result.status).toBe('succeeded_with_issues')
+          // 先到行保留、后到不静默覆盖——同公开路径是真实冲突（同站命名空间不重不解）
+          const assets = (await db.execute(`select source_id, source_url, public_path, status
+            from media_assets where site_id = '${reg.siteId}' order by source_id`)) as any
+          expect(plain(assets)).toStrictEqual([
+            {
+              source_id: '971',
+              source_url: 'https://fixture.example/wp-content/uploads/2026/10/dup.png',
+              public_path: '/wp-content/uploads/2026/10/dup.png',
+              status: 'ready',
+            },
+          ])
+          const report = await readReport(work, result.jobId)
+          expect(report.counts).toStrictEqual({
+            mediaRegistered: 1,
+            mediaFromSidecar: 0,
+            mediaMissing: 0,
+            mediaQuarantined: 0,
+            mediaDanglingRefs: 0,
+            mediaAmbiguous: 0,
+          })
+          const conflict = report.issues.filter((i) => i.includes('public_path 冲突'))
+          expect(conflict).toHaveLength(1)
+          expect(conflict[0]).toContain('972')
+        } finally {
+          await cleanupSiteRows(db, reg.siteId)
+        }
+      } finally {
+        await rm(work, { recursive: true, force: true })
+      }
+    })
+  })
+
   it('幂等重跑：media_assets/media_usages 零增行、mediaRegistered=0；悬空引用按流如实再现', async () => {
     await withTestDb(async (db) => {
       const work = await mkdtemp(join(tmpdir(), 'sf-media-idem-'))