uploadComposerAttachment's remote/local decision (image.attach vs
image.attach_bytes) read $connection.get()?.mode — the window's ambient
connection — at all three call sites. Since the multi-connection
routing work landed, a session can be owned by a different, registered
connection than the ambient one (Bot Mode, the unified Sessions list):
the RPC itself already routes to that owner via requestForSessionProfile,
but the byte-vs-path decision did not, so a local-ambient window chatting
in a remote-owned session shipped a client-local composer-images path to
a backend that can't read it (#94640).
isSessionRemote() resolves the session's own owner route (falling back to
ambient only when no owner route is known, matching the existing RPC
routing behavior in session-states.ts) and replaces the three ambient
reads in use-prompt-actions/index.ts, session-tile-actions.ts, and
user-edit-composer.tsx.
chelsealong
6b3977b577