feat: tab ownership — isolate harness tabs from the user's browsing

Track which page targets this harness session opened so the agent can never
attach to, switch to, or close a tab the user opened themselves. New tabs
are spawned in a dedicated Chrome window (newWindow:true on first open,
openerId chaining after) so harness activity stays visually separate.

- new OwnershipRegistry (src/cdp/ownership.ts) tracks owned targetIds and
  the harness window seed; mutations notify a single listener that persists
  to BrowserState (ownedTargetIds, harnessWindowTargetId)
- attachFirstPage prefers an already-owned live target; otherwise opens a
  fresh harness-owned tab in its own window instead of grabbing whatever
  page the user is on
- session subscribes Target.setDiscoverTargets and reaps targetDestroyed
  events so the registry stays in sync with reality
- listTabs returns owned:boolean per tab and reconciles dead ids
- browser_list_tabs defaults to scope:"owned"; pass scope:"all" to inspect
  the user's other tabs (read-only — they cannot be switched to or closed)
- browser_switch_tab refuses non-owned tabs, with a clear remediation hint
- browser_new_tab opens inside the harness window via openerId, falling
  back to a fresh window when the seed has been closed
- new browser_close_tab tool — owned tabs only, supports unique hex prefix

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/registry.ts b/src/registry.ts
index d9b7cea..d205bf6 100644
--- a/src/registry.ts
+++ b/src/registry.ts
@@ -9,7 +9,7 @@ import { handleDialogTool } from "./domains/dialog";
 import { screenshotTool } from "./domains/screenshot";
 import { navigateTool, openUrlsTool } from "./domains/navigate";
 import { goBackTool, goForwardTool, reloadTool } from "./domains/history";
-import { listTabsTool, currentTabTool, switchTabTool, newTabTool } from "./domains/tabs";
+import { listTabsTool, currentTabTool, switchTabTool, newTabTool, closeTabTool } from "./domains/tabs";
 import { uploadFileTool, downloadTool, printToPdfTool } from "./domains/files";
 import { viewportResizeTool } from "./domains/viewport";
 import { dragAndDropTool } from "./domains/drag";
@@ -39,6 +39,7 @@ const TOOLS: ReadonlyArray<AnyBrowserToolDefinition> = [
   currentTabTool,
   { ...switchTabTool, serialized: true },
   { ...newTabTool, serialized: true },
+  { ...closeTabTool, serialized: true },
   { ...uploadFileTool, serialized: true },
   { ...downloadTool, serialized: true },
   { ...printToPdfTool, serialized: true },