v5.7.0

The live-preview carrier stops living in your project, reports what it
refused, and rides an engine that tells you when the browser turned your
extension away.

Fixed

• The live-preview carrier is no longer a permanent resident of the
  project. extension_stop removes it, extension_build removes it
  before the build runs (and refuses to call a build clean if it ever
  finds the carrier in dist/), and extension_dev carrier: true adds
  it to .gitignore so the first git add -A cannot vendor it. Every
  path is marker-guarded: a directory the tool did not place is reported,
  never removed.

• extension_open no longer navigates away whatever page the caller was
  watching. It reuses only a disposable tab (blank, new-tab page, or a
  tab already on the same extension origin) and otherwise opens a new
  background tab, so a trace page keeps its carrier registration.

• extension_open treats a client-side redirect as a landing instead of
  reporting NavigateFailed, and reports where the page went. A failed
  http(s) navigation no longer sends the caller off to debug their own
  bundle.

• extension_open confirms with the browser that a UI surface actually
  opened. When the engine reports the surface opened and no document
  target appears, the result says so (SurfaceDidNotOpen) and points at
  asTab: true, instead of handing back a green answer for a surface
  that is not there.

• The bundled carrier payload answers with its real results. Every
  backend method returns the promise it was given instead of a shape,
  so a chrome.* call that rejects reaches the caller as a failure;
  executeScript refuses func/code forms it cannot honor, offscreen
  close is verified, and downloads.erase is implemented. A refusal now
  rides a refused disposition from the refusal site through the carrier
  into the trace, so refused calls stop being badged as real work and
  stop earning coverage. Storage rows correlate on a canonical key (one
  call, one row), tab facts survive both directions, and the event port
  replays its backlog to a page that connects late.

Changed

• The engine this server spawns when a project has no local install is
  pinned to 4.0.16-canary.1784889479.74e12044. Two behaviors are worth
  the prerelease: EXTENSION_HEADLESS is finally honored, so an agent
  driving extension_dev cannot open a window on the operator's screen,
  and a browser refusing to load the extension is reported as an error
  instead of a session that claims to be ready. extension_wait already
  surfaces both through the ready contract. This pin returns to a stable
  release once 4.0.16 ships. A project with its own extension install
  is unaffected, and EXTENSION_MCP_CLI_VERSION still overrides.
• extension_deploy and extension_store_status advertise safari
  again: the platform's Safari/App Store submission lane is now enabled
  for every project, so the store enum and the per-store status report
  treat it like chrome, firefox, and edge.

Added

• extension_dev accepts carrier: true (Chromium-family sessions): it
  places the bundled Extension.dev Live Preview carrier in the project's
  ./extensions folder, which Extension.js auto-loads as a companion
  beside the extension under development. Pages the carrier allowlists
  (inspect.extension.dev, localhost) can then pair with the live session
  and stream its real-lane chrome.* session trace over the carrier's
  event port. The copy is marker-guarded: an existing unmanaged
  extensions/extension-dev-live-preview directory is never overwritten,
  and the tool result reports what happened either way. The prebuilt
  payload ships in the package under extensions/live-preview.