Keep in-session /model picks from leaking into the global default

[payne0420]

Problem

Claude Code v2.1.153+ persists an in-session /model pick (pressing Enter in the picker) to the user-global settings file (~/.claude/settings.json, the model key). Under UltraCode the picker lists proxy-only ids (e.g. claude-composer, claude-gpt-5.5-codex), so picking one silently makes it your global default — and a plain claude run outside the proxy then fails, because the real Anthropic API doesn't recognize that id.

The launchers set the session model via --settings + --model (both session-scoped, never persisted), so the launcher itself never pollutes globals — but an interactive /model Enter-pick does, and there's no Claude Code flag/env to disable that persistence.

Fix

Both launchers now snapshot the global model key before launch and restore it on exit, so /model picks stay session-scoped:

• bin/ultracode — snapshot_global_model before start_proxy; restore_global_model inside the existing stop_proxy EXIT trap.
• windows/Start-UltraCode.ps1 — Save-GlobalModel / Restore-GlobalModel at the equivalent points.

Both do the JSON edit by shelling out to Python (already required by the launchers) rather than re-serializing the whole file, so only the model key is touched and the rest of settings.json is left intact. (On Windows this also avoids ConvertTo-Json collapsing single-element arrays in nested blocks like hooks.)

Behavior

• Ref-count-safe across concurrent sessions: a clean start snapshots, a session that joins a running proxy keeps the existing snapshot (so a mid-session pick isn't captured as the "original"), and the last session out restores, then removes the saved-state file.
• Restores the prior value, or removes the model key entirely if there wasn't one before.
• Picking with /model still applies for the current session; it's just reverted globally on exit.
• Opt-out: UC_PRESERVE_GLOBAL_MODEL=0 restores Claude Code's normal persist-globally behavior.
• Native alternative for a one-off: press s in the /model picker (session-only, never saves) — documented too.

Docs

docs/TROUBLESHOOTING.md gains a section describing the symptom, the guard, and the escape hatch.

Testing

• Round-trip verified for both cases: restores a prior model, and removes a model the session added when none existed before — permissions/hooks/other keys preserved.
• bash -n bin/ultracode clean.
• python3 test_proxy.py → ALL TESTS PASSED; python3 scripts/doctor.py → 17 ok, 0 failures.

No changes to proxy.py; this is launcher-only and independent of other open PRs.

🤖 Generated with Claude Code