Detect and reject placeholder filesystem paths before tool execution

Description

Summary

When using local models (Qwen3, DeepSeek, etc.), the model may generate placeholder filesystem paths such as:

/absolute/path/to/file.md

instead of a valid workspace-relative path.

Currently OpenCode interprets this as a real absolute path and asks the user for permission to access an external directory.

Reproduction

Workspace:

~/Documents/mind

Prompt:

create file.md with no content

Model output:

Write("/absolute/path/to/file.md")

OpenCode requests permission to access:

/absolute/path/to/

instead of recognizing this as a placeholder.

Expected behavior

OpenCode should detect common placeholder paths before executing filesystem tools.

Examples:

/absolute/path/to/*
/path/to/*
/your/path/*
/tmp/example/*

These should be treated as invalid placeholder values instead of real filesystem locations.

Possible response:

The model generated a placeholder path. Please provide a valid workspace-relative path.

Why this matters

This is not specific to Qwen.

Many local models occasionally emit placeholder values copied from training examples.

Detecting these placeholders would make filesystem tools much more robust regardless of the model being used.

Plugins

None

OpenCode version

1.18.5

Steps to reproduce

No response

Screenshot and/or share link

Steps to reproduce

1. Start OpenCode inside a project workspace.

cd ~/Documents/mind
opencode

2. Use the following model:

qwen3:latest (Ollama)

3. Ask the assistant:

create file.md with no content

4. Observe that the model invokes the filesystem tool with the following path:

/absolute/path/to/file.md

5. OpenCode requests permission to access an external directory:

Access external directory
/absolute/path/to/

Operating System

Ubuntu 25.10

Terminal

Christian Hergert 49.1