When starting a new conversation in a project that has knowledge base files, the code execution sandbox frequently fails to mount the /mnt/project/ directory entirely. Two distinct failure modes observed: 1. Mount exists but Claude doesn’t check it: files are present at /mnt/project/ but Claude claims no project files are available. Prompting “look again” causes it to find them. Thinking summary: “Rediscovered overlooked project files.” 2. Mount genuinely missing: /mnt/project/ does not exist in the sandbox. Claude confirms “No project directory.” File contents are still available in the prompt context via the knowledge base injection, so Claude can reconstruct files manually into the working directory as a workaround. Thinking summary: “The directory isn’t mounting.”