The browser tool's open action only passed the requested timeout to acquireTab; acquireBrowser ran under the caller signal alone, so CDP discovery/connect could run through its own fixed 5s/30s waits past the requested deadline. A freshly-created browser also sat in the registry at refCount 0 during worker/surface acquisition: the worker-abort branch released it only on tempHold (never on the fresh refCount-0 case), orphaning the handle, and two different-name opens sharing one refCount-0 browser let a single failure dispose it out from under the survivor.
Compose one open deadline from the caller signal and params.timeout and thread it through both acquireBrowser and acquireTab; caller cancellation stays ToolAbortError, the requested timeout becomes a timeout ToolError. Hold one explicit registry lease across tab acquisition, released exactly once on the mutually-exclusive success/rollback paths, and make the worker-abort browser release mirror the error paths' refCount-0 check.
Fixes#6365
