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Validate images before they enter conversation context - #33
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The CLI's Read tool detects images by file extension and base64-encodes them into content blocks. If a file has an image extension but contains non-image data (e.g. an HTML redirect from an auth-gated URL), the API rejects it with 400 "Could not process image". The bad block persists in conversation history, causing every subsequent turn to fail. Layer 1 — PreToolUse hook on Read: - Check magic bytes (PNG/JPEG/GIF/WebP signatures) and file size (<5MB) - Deny Read with clear error message if invalid — conversation intact - Detects HTML pages saved with image extensions Layer 1b — Nerve-sourced image validation (Telegram pipeline): - Validate base64 data before constructing content blocks - Replace invalid images with descriptive text block Layer 2 — Error handler railguard: - Detect "Could not process image/document" in generic exception handler - Clear sdk_session_id so next turn starts fresh CLI (no --resume) - Last resort for images entering via MCP tools or CLI internals Also fix pre-existing test_proxy failure: test_non_interactive_proxy_mode leaked host ANTHROPIC_API_KEY through patch.dict(clear=False).
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Summary
test_non_interactive_proxy_mode— hostANTHROPIC_API_KEYleaked throughpatch.dict(clear=False)Context
On April 3, session
665441degot stuck in an infinite error loop after attempting to read images from a private GitHub issue. The CLI's Read tool base64-encoded what was likely an HTML auth redirect page (saved with a.pngextension), and the API rejected it. Since the CLI re-sends full conversation history on every turn, the bad image block poisoned the entire session.Test plan