v4.2.2

Agent-ergonomics release from the 4.2.1 fresh-eyes walk: the two changes
that removed nearly all friction a real MCP client hit.

• Session-aware browser default. Tools that target a running session
  (extension_logs, extension_reload, extension_eval,
  extension_storage, extension_open, extension_dom_inspect,
  extension_list_extensions, extension_source_inspect,
  extension_wait) no longer hard-default browser to a constant that
  could disagree with the session extension_dev actually started.
  Omitting browser now resolves to the active session's browser:
  in-memory registry first, then the freshest live ready.json contract
  on disk (dead pids ignored), then the old constant. Starting a session
  with browser: "chrome" and calling extension_logs with no args now
  just works instead of erroring about a missing chromium channel.
• Error hints speak the MCP tool surface, not the CLI. Act-verb error
  prose is rewritten before returning: `extension dev --browser=chromium --allow-control` becomes extension_dev with { browser: "chromium", allowControl: true }, and stray
  --allow-control / --allow-eval / --browser=<x> mentions become
  their tool-argument names. Result data is never touched — only
  error/hint prose. Tool descriptions now name allowControl /
  allowEval directly, so agents no longer discover the gates by
  fuzzing the schema.
• The no-channel error now names the session that IS running ("Active
  session browser(s) for this project: chrome — pass that as browser"),
  so an agent retargets instead of spawning a second, conflicting
  session. Same for the extension_logs follow miss.
• extension_list_extensions / extension_source_inspect accept
  browser: "chromium" (the default dev target) instead of rejecting it
  as non-Chromium.
• Tests: session-browser resolution + hint-translation suite (137 total).