v0.50.0

Three defects seen in one afternoon on the interface, each with its cause one step upstream of where it showed.

**The browser closed and reopened on a domain that did not resolve.** The retry wrapper treated every exception as a dead browser: it discarded the healthy one, with its cookies and pages, built a replacement as the same person and ran the action again, which failed identically. Only a browser that is gone is rebuilt now, and what "gone" means lives in one place, next to the check that decides it between calls.

**The main browser came up on screen at a launch that had asked for nothing of the kind.** The session file carried `headless: false` from a headed process that had used the same file name, and the restore took the file's word over this process's. Whether a window is shown is a property of the launch, like the engine, so it is no longer written down and the restore reads it from the environment alongside the engine.

**The live pane froze on a page the browser had left two sites earlier.** The engine's window capture ends for good when a headed window is minimised, without telling anybody, and the session served the last frame it held forever. A frame older than two seconds now restarts the capture, and a restart that stays silent is dropped with the reason. Measured on a still page first: the engine delivers 93 frames in four seconds, so silence is not quiet.

Every branch is held by a test that was seen red against the code it replaces, and the minimise case by an e2e test against the real engine. Version 0.50.0.