mobile-desktop: model switch in phone app doesn't update desktop composer for same thread #15190

Summary

Switching the model in the T3 Code mobile (phone) app does not update the selected model shown in the T3 desktop UI for the same thread, even though the switch takes effect for subsequent runs.

Environment

• opencode version: 2.0.22
• OS: Linux hp-laptop 7.0.0-34-generic feat: Checkpointing #34-Ubuntu SMP PREEMPT_DYNAMIC Wed Sep 2 14:29:37 UTC 2026 x86_64 GNU/Linux
• Terminal: xterm-256color (TERM_PROGRAM unset)
• Shell: /bin/bash
• Install/channel: release (opencode v2.0.22 from ~/.opencode/bin/opencode)
• Active plugins: none found in config (~/.config/opencode/opencode.jsonc contains only $schema)
• T3 Code desktop version: 0.0.46-nightly.20261003.2623
• T3 Code mobile build: 2.0.0

Reproduction

1. Open the same T3 thread on both phone app and desktop app, using the opencode provider.
2. Confirm both show model A (e.g. opencode/space-bunny-free).
3. In the phone app, switch that thread to model B (e.g. opencode/muse-spark-1.3-contributor-free).
4. Send a message from the phone (e.g. "Testing again") — it runs with model B.
5. Observe the desktop UI: composer / thread header still shows model A.

Expected Behavior

A durable per-thread model switch made on one client (mobile) should update every open client (desktop) displaying that same thread. Displayed model and model used for the next run should agree.

Actual Behavior

Phone app switches and runs with the new model, but desktop UI keeps showing the old selected model. Stale display persists without manual refresh / re-open of thread.

Additional Context

• Provider observed: opencode, models space-bunny-free -> muse-spark-1.3-contributor-free. Unknown if Claude/Codex providers also affected.
• Frequency: reproduced at least once consistently in this thread (message sent as space-bunny, next run as muse-spark, desktop stale).
• Related upstream: anomalyco/opencode#35802 (tui: synchronize durable model switches across V2 clients) — same class of bug: durable Session.Info.model updates but second client's composer keeps one-time hydrated model. That tracker was closed after V2 lifecycle rework with instruction to file fresh focused issues.
• Related: anomalyco/opencode#6946 (desktop session out of sync with TUI), #19264 (session not sync desktop/web).
• No duplicate found in pingdotgg/t3code via search for mobile desktop model sync.
• Workaround: Unavailable — refresh / re-open thread suspected to fix display, not yet confirmed.