Follow-up to #86916. That fix gave named sessions their own daemon
(socket/log/pid) and their own provider browser — but on a SHARED local
Chrome / CDP browser, a fresh named daemon still attaches to the first
existing page, the same page a sibling daemon may hold. A named session
that never calls new_tab() could still stomp another's tab.
browser_exec now prepends a small preamble to the model's code for named
sessions on shared browsers: once per daemon process (marker keyed by
uid + BU_NAME + daemon pid), it creates a fresh tab via
Target.createTarget and switch_tab()s onto it before any model code
runs. Private per-name browsers (provider-keyed bu-named-<name>, or
direct-API Browser Use cloud) skip the preamble via an internal env
sentinel popped before launch — there's nobody to collide with, and the
extra tab would leak.
Best-effort by design: if the preamble's CDP calls fail, behavior
degrades to pre-fix, never blocks the exec.
E2E against a shared headless Chrome with the STOCK harness: two named
sessions issuing bare js() writes (no new_tab) kept distinct state
(EDGE-A/EDGE-B read back intact); the sabotage run without the preamble
reproduced the clobber (both read EDGE-B). Removes the dependency on the
upstream browser-harness tab-isolation PR for correctness.
Teknium
c9a806e9d2