lifecycle object on every response adds ~10k tokens per session over MCP

[giri256]

Every successful command response carries a lifecycle object, including in MCP tool results:

"lifecycle": {"effectiveLaunch": {"browserLaunched": ..., "engine": ..., "launchHash": ...}, "launched": ..., "relaunchedBrowser": ..., "restartedBackground": ..., "restoreStatus": ..., "saveStatus": ...}

It shows up on wait_ms, get_url, click, and so on, where nothing about the launch changed. For an agent it matters once per session, or when something actually happened (a launch, a relaunch, a restore). The rest of the time it is noise in the model's context.

Measured: over one Claude Code session with 96 agent-browser MCP calls on 0.39.0, the lifecycle blocks added about 36k characters (~10k tokens) of output. That figure counts both copies of the payload; #2092 removes the duplicate copy, which halves it but doesn't remove it. A click or wait_ms result is roughly 550 to 750 characters, and most of that is lifecycle.

Suggested fix (either):

• Include lifecycle only when something in it is not the steady state (launched, relaunchedBrowser, restartedBackground true, or a restore/save status worth reporting).
• Or keep it in --json CLI output but drop it from MCP structuredContent unless it carries news.

The object is added in cli/src/main.rs (mark_restarted_background) and cli/src/native/actions.rs. Since it is part of the --json contract, I'm filing this as an issue rather than a PR so you can pick the shape.