Model ID auto-switches silently during session

[smithyyang]

Description

The model ID used in a session auto-switches silently (no error, no prompt) to a different model, both at restart time and mid-conversation. There is no fixed pattern — switches observed between OpenAI models and DeepSeek models, and vice versa.

Steps to Reproduce (observed, not perfectly consistent)

1. Start a session with an explicitly set model.
2. Either restart OpenCode or continue a long conversation.
3. At some point, the session silently starts using a different model (e.g. deepseek-ai/DeepSeek-V4-Flash or another model) without any notification.

Expected Behavior

The model should remain stable throughout the session unless the user explicitly changes it (via /model or config edit). Any automatic fallback or switch should be clearly communicated to the user.

Actual Behavior

The model switches silently. The user only notices because response behavior changes (e.g. sudden loss of reasoning, different response style).

Environment

• OpenCode version: latest
• Observed with gpt-5.4-mini → deepseek-ai/DeepSeek-V4-Flash and other combinations
• No error messages in logs

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• After integrating oh-my-opencode, the conversation sent will automatically switch to the Claude Opus 4.6 model #16313: Model auto-switches to a different model silently after sending a message (same symptom: session model changes to a different model without user action)
• UI model picker silently resets to agent's default after first message in new session #23666: UI model picker silently resets to agent's default after first message in new session (same symptom: model selection does not persist; now closed/resolved)

If your issue is distinct from these (e.g. it occurs mid-conversation rather than only on the first message, or involves provider routing logic rather than UI picker state), please add a comment clarifying the difference.

[smithyyang]

This issue is distinct from #16313 and #23666:

1. Not UI-related — this is the CLI version, not the web UI model picker.
2. Occurs mid-conversation — not only on first message or restart. The model can switch halfway through a long session.
3. Silent, no error — no notification, no log message, no fallback indicator.

This suggests the issue may be in the provider/model routing logic rather than in UI state persistence.

[rekram1-node]

are u using plugins?

[smithyyang]

are u using plugins?

what i use is dcp ,"@tarquinen/opencode-dcp@latest",just this

[rekram1-node]

maybe share opencode debug config