Infinite retry loop on folder read with images; bad image_url payload (400) and ignored interruption

Title: Infinite retry loop when “read folder” hits an image; sends text/markdown as image_url (400), ignores user interruption

Description
Requesting the agent to read a folder with mixed content caused it to attempt processing an image. The run entered an unescapable retry loop after a 400 error. Interrupting and changing instructions had no effect; the session had to be quit. The API error indicates the agent constructed an image content payload with MIME text/markdown instead of a proper image data URL.

Environment

• CWD: D:\\brain-dev
• OS: Microsoft Windows NT 10.0.26220.0
• Shell: PowerShell 7.5.2
• Git: 2.49.0.windows.1
• Codex CLI: 0.27.0
• Sandbox: workspace-write
• Approvals: on-request
• Network: restricted

Steps to Reproduce

1. Prepare a folder with .md files plus *.png/*.jpg.
2. Ask the agent to “read this folder”.
3. Observe attempts to open an image → 400 → loop.
4. Try interrupting; loop persists until quitting.

Actual Behavior

• Agent tried to process an image during folder read.
• Built image_url with MIME text/markdown.
• Entered retry loop; ignored interruption.
• Required quitting the session.

Expected Behavior

• Reads only text by default; images opened only if requested.
• Images sent as data:image/*;base64,... when needed.
• 4xx validation errors are non-retryable; agent adapts or asks.
• User interruptions halt retries immediately.

Error Log

unexpected status 400 Bad Request: {
  "error": {
    "message": "Invalid 'input[28].content[0].image_url'. Expected a base64-encoded data URL with an image MIME type
(e.g. 'data:image/png;base64,aW1nIGJ5dGVzIGhlcmU='), but got unsupported MIME type 'text/markdown'.",
    "type": "invalid_request_error",
    "param": "input[28].content[0].image_url",
    "code": "invalid_value"
  }
}

Impact

• Blocks mixed-folder reads; high workflow disruption.

Suspected Root Cause

• Misclassification of file type leading to building an image_url with text/markdown.
• Missing MIME detection and data-URL encoding for images.
• Retry policy treats 4xx validation errors as retryable and doesn’t respect user override.

Proposed Fixes

• Robust MIME/type detection; only send images as data:image/*;base64,....
• Default skip binary files for “read folder”; prompt to open images.
• Treat 4xx invalid_request_error as non-retryable; stop and ask.
• Ensure user interruption cancels queued retries/steps.
• Provide “list-only” and “read-only .md/.txt” modes.

Workarounds

• “List filenames only; skip images/binaries.”
• “Read only .md files in FOLDER; do not open images.”
• Manually list: rg --files -g "!**/*.{png,jpg,jpeg,gif,webp}"