fix(gateway): bridge terminal config when multiplexing profiles

[Baophan00]

Bug

When a multiplexed gateway routes a turn to a secondary profile, only hermes_home and the secret scope were switched. The TERMINAL_* env vars still carried the gateway profile's backend. A routed profile with terminal.backend: docker silently ran commands on the gateway's local backend — the sandbox was never entered.

Fix

Bridge the routed profile's terminal: section from its config.yaml into os.environ inside _profile_runtime_scope. Save the original TERMINAL_* values before bridging and restore them when the scope exits, so the next turn's profile sees its own terminal config.

[100yenadmin]

Heads up — this and #79117 both target #68559 (terminal config leaking across routed profiles), and a reviewer asked us to consolidate around one approach.

I've folded the coverage here into #79117: it uses a ContextVar terminal-config scope and routes every TERMINAL_ENV/TERMINAL_CWD read through a single accessor (including the env_probe cache and prompt_builder backend-probe paths), with a guard test that fails on any new direct env read. Your bridge approach is lighter; the ContextVar one covers a few more read sites and the cross-profile probe-cache case. Not trying to step on this — flagging so a maintainer can pick one rather than merge overlapping fixes, and happy to align on naming either way. Thanks for digging into the same bug.

[teknium1]

Thanks for this PR. Merged via #101242 (4a7f228) on current main — routed multiplex profiles get their own terminal cwd/backend/docker config; container boot honors config multiplex_profiles.

#101242 won as the consolidated fix because it covers the whole multiplex-profile bug class in one change (with tests) rather than the single symptom addressed here; this PR is superseded by it.
Your PR is referenced in #101242's body as prior work on this bug.

If anything from your original change is still missing on main >= 4a7f228, please open a fresh PR/issue against main and tag it. Thanks again.