Bug Model enters infinite loop due to hallucinated oldString in edit tool calls

[stevensli]

Description

While using the edit tool to fix a simple syntax error in a Rust file, the model (gemma4-31b) entered a repetitive failure loop.
Steps to Reproduce:

1. The model calls read to get the content of a file.
2. The read tool returns the actual content (e.g., if guess << secret secret_number {).
3. The model attempts to call edit, but instead of using the string returned by read, it hallucinates a different string for oldString (e.g., if guess <<< secret secret secret_number {).
4. The edit tool correctly returns an error: "Could not find oldString in the file."
5. The model ignores this error and repeats the exact same incorrect edit call multiple times (10+ times) without updating the oldString to match the actual file content.
   Expected Behavior:
   The model should prioritize the output of the read tool and, upon receiving a "not found" error from the edit tool, it should re-examine the file content and correct the oldString parameter.
   Actual Behavior:
   The model ignores the tool's error message and persists in using a hallucinated string, resulting in an infinite loop of failed tool calls.
   Environment:

• Model: gemma4-31b (local-vllm/gemma4-31b)
• Tool: edit

Plugins

No response

OpenCode version

1.3.14, 1.3.17, 1.4.0, 1.4.3

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

No response

Terminal

No response

[github-actions]

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

• Subagent enters infinite retry loop on edit/write tool failure, causing excessive API costs #17169: Subagent enters infinite retry loop on edit/write tool failure — same core behavior of the model repeatedly retrying a failed edit call without stopping
• gemma-4-26b and gemma-4-31b opencode interaction issues leading to tool loops/failures #21034: gemma-4-26b and gemma-4-31b opencode interaction issues leading to tool loops/failures — same model family (gemma-4) exhibiting tool call loops/failures in OpenCode
• Edit/write tools enter infinite retry loops when external processes modify files (stale FileTime) #19040: Edit/write tools enter infinite retry loops when external processes modify files — related infinite retry loop on edit tool failure (different trigger, same loop behavior)

Please review these issues to see if your report is already covered, and consider adding your findings there if so.

[BrutchsamaJeanLouis]

there is also issue 16531 that blocks gemma4 support