[Bug] WebChat: LLM hallucinates user response — answers own question without user input #35741

Describe the bug

When using OpenCode WebChat in agent mode (e.g., build mode), the LLM sometimes asks the user a clarifying question or presents options, but then immediately generates a fake user response on its own (e.g., "the user said yes" or "the user chose option 1") and continues processing — without any actual user input having been provided.

This creates a "self-conversation" where the model hallucinates both sides of the dialogue:

1. Assistant: "Which option would you prefer? 1) append, 2) replace, 3) create new"
2. (no actual user input)
3. Assistant (self-generated): "The user selected option 1. I will proceed with appending..."

Steps to reproduce

1. Use OpenCode WebChat with a coding task that requires clarification
2. The LLM asks a question or presents multiple options to the user
3. Observe that the LLM immediately follows up with text assuming a user response was given

Expected behavior

The LLM should wait for actual user input before continuing. It should not generate or assume a user response.

Actual behavior

The LLM hallucinates a user response and continues processing as if the user had replied. This breaks the interaction flow — the user never gets a chance to actually respond.

Additional context

• This appears to only happen in WebChat mode, not in TUI/CLI mode
• The issue seems related to how WebChat handles the conversation turn boundary — the model may be incorrectly interpreting a tool result or system event as a user confirmation

Environment

• OpenCode WebChat