`ensureGatewayAgent` is the (connectionId, profile) door the SDK's `ensureAgent`
goes through, and it landed on main after the profile path was made atomic. It
published in the order the profile path used to:
await ensureGatewayForAgent(connection, target) // $gateway flips here
$activeGatewayProfile.set(target)
await syncConnectionToActiveAgent(connection, target) // $connection here
The trailing await is the same mixed-state window: $gateway and
$activeGatewayProfile already name the agent's backend while $connection still
describes the previous one, so any request or plugin mode-listener firing in
that window announces the wrong mode to the new backend.
Both doors now share one seam:
* `prepareGatewayForAgent` mirrors `prepareGatewayForProfile`: dial the socket,
publish nothing, return the synchronous activation thunk. A local/null
connection falls through to the profile seam, so the two paths cannot drift.
`ensureGatewayForAgent` becomes `(await prepareGatewayForAgent(...))()`,
exactly how `ensureGatewayForProfile` relates to its own prepare.
* `syncConnectionToActiveAgent` splits into `resolveConnectionForActiveAgent`,
which resolves only. `ensureGatewayAgent` resolves the descriptor and dials
the socket concurrently, then activates, moves the profile pointer and sets
the descriptor with no awaits between them.
The best-effort contract on this path is unchanged on purpose: a descriptor
lookup that fails still leaves the previous `$connection` in place rather than
aborting the switch, which is what the profile path does instead. That
difference is deliberate and called out for review rather than quietly
harmonised.
Tests: `profile-agent-activation.test.ts` gains
`never publishes the agent gateway before its connection descriptor`, the mirror
of the profile-path test, asserting a pending `getConnectionFor` leaves all
three atoms on the old backend and that they flip together once it resolves. The
existing mutex and resync tests move onto the prepare/publish mocks, which also
repairs them: that file mocked `@/store/gateway` without `prepareGatewayForProfile`,
so its profile-path cases called an undefined mock after the rebase.
Jack Lau
d0e0951cf1