[FEATURE]:do not auto-convert image paths to attachments when the model does not support image input #42544

Feature hasn't been suggested before.

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Describe the enhancement you want to request

Problem

When typing a path ending with an image extension (e.g. /path/to/chart_actual.png) in the TUI, opencode automatically recognizes it and attaches it as an image attachment (shown as [Image 1] in the message).

If the current model does not support multimodal/image input, the model errors out:

ERROR: Cannot read "chart_actual.png" (this model does not support image input).

Steps to reproduce

1. Start the opencode TUI with a text-only model (one that does not support image input).
2. Paste a full path ending with .png (or .jpg/.jpeg, etc.), e.g. /Volumes/RamDisk/chart_actual.png.
3. Send the message.
4. Observe: the path is auto-converted to an [Image 1] attachment, and the model errors out with "image input not supported".

Workarounds tried (all imperfect)

• Adding a trailing space / wrapping in backticks / adding a text prefix (e.g. image: /path.png): still intercepted as an attachment whenever a cmd+V paste triggers.
• Using a Markdown link [/path/image.png](): bypasses it, but is unintuitive and not applicable to every paste scenario.

Suggestion

Before auto-detecting a path as an image attachment, opencode should check whether the current model supports image input (i.e. whether the model's modalities include image):

• Supports images: keep the current auto-attach behavior (convenient for multimodal models).
• Does not support images: keep the text as-is (plain path), do not convert it to an attachment.

Environment

• opencode version: latest
• Platform: macOS
• Interface: TUI