feat(browser): complete camofox BrowserProvider with tabs, interaction, download capture and control lease

Contracts for browser API and browser.* agent capabilities; adapter implements
close/list/restore sessions, tabs + reconcile, history, click/type/select/scroll/press,
extract, waitForDownload (staged via DownloadSink, sha256), stale-ref guard and
automation/human actor check. testkit mock camofox gains an interactive site
(login redirect, captcha, click-driven page changes, downloads, PNG screenshots).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/contracts/src/capability.ts

@@ -72,6 +72,10 @@ export const CAPABILITY_IDS = [
   "site.health_check",
   "site.refresh_login",
   "site.user_data",
+  "browser.snapshot",
+  "browser.navigate",
+  "browser.interact",
+  "browser.download",
 ] as const;
 export const KnownCapabilityId = z.enum(CAPABILITY_IDS);
 export type KnownCapabilityId = z.infer<typeof KnownCapabilityId>;
@@ -348,6 +352,52 @@ export const CAPABILITY_CATALOG: Record<KnownCapabilityId, CapabilityDescriptor>
     true,
     false,
   ),
+  // C1-E 浏览器能力(REQ §4.4、§4.7.3):经 BrowserProvider 访问用户已有的 camofox-browser;
+  // 导航限站点域名,凭证由服务端注入,人工接管期间自动化动作被拒;下载产物只进后端暂存核验
+  "browser.snapshot": d(
+    "browser.snapshot",
+    "读取原站页面",
+    "读取站点浏览器会话当前页面的结构化快照(可访问性文本 + eN 元素引用,凭证已遮蔽);控制权交还或导航后必须重新读取",
+    "read",
+    "BrowserSnapshot",
+    "read",
+    "low",
+    true,
+    false,
+  ),
+  "browser.navigate": d(
+    "browser.navigate",
+    "打开原站页面",
+    "在站点浏览器会话里打开站点域名内的地址(没有会话时按站点打开);受站点限流、超时与重试预算约束",
+    "execute",
+    "BrowserNavigate",
+    "admin",
+    "low",
+    false,
+    false,
+  ),
+  "browser.interact": d(
+    "browser.interact",
+    "操作原站页面",
+    "在站点浏览器会话里点击 / 输入 / 选择 / 滚动 / 按键;登录字段用 credential 由服务端注入凭证;验证码或二次认证用 request_human 转人工",
+    "execute",
+    "BrowserInteract",
+    "admin",
+    "medium",
+    false,
+    false,
+  ),
+  "browser.download": d(
+    "browser.download",
+    "捕获原站下载",
+    "捕获浏览器会话里的种子下载,交后端暂存并核验 infohash、匹配本地资源;提交下载仍用 download.plan / download.submit",
+    "execute",
+    "BrowserDownload",
+    "organize.execute",
+    "medium",
+    false,
+    false,
+  ),
 };
 
 function d(