[remote-controlled-man]

Fixes #971.

Attachments passed through Bash process substitution, such as llm "Describe this image" -a <(cat image.png), could not be detected because MIME probing expects a seekable file. With an explicit --at type, hashing and subsequent reads could instead consume the pipe and lose its content.

Read FIFO attachments once and retain their bytes for type detection, model requests and logging. Both -a and --at use this behavior; regular file attachments keep their resolved paths.

Validation: full pytest suite, Black, mypy, Ruff, Cog, package build and plugin-loading script. Regression coverage checks both CLI options, repeated content reads and stored attachment bytes; the Bash process-substitution command was also exercised with the local echo model.

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[simonw]

Nice fix:

~/dev/llm % uv run llm "Describe this image" -a <(cat zelda-card.jpg)
Usage: llm prompt [OPTIONS] [PROMPT]
Try 'llm prompt --help' for help.

Error: Invalid value for '-a' / '--attachment': Could not determine mimetype of /dev/fd/11
~/dev/llm % gh pr checkout 1857                               
M	tests/test_chat.py
Switched to branch 'codex/prflow-5e6c84af647a'
~/dev/llm % uv run llm "Describe this image" -a <(cat zelda-card.jpg)
**Describing the handheld device**

I need to describe the image of a handheld gaming device. It has a transparent blue case and a screen displaying pixel art that resembles a Zelda-like game, possibly from emulation, with overlay control mappings. I don’t need to identify any specific game, just focus on the retro game style and character map. The device appears close-up, resting against a dark gray background, showcasing its buttons. I’ll ensure not to include anything unsupported.
A close-up of a small handheld gaming device in a translucent blue case. Its screen shows a colorful, top-down pixel-art adventure game, with a character on a path amid green grass, water, and stairways. Blue emulator-style labels and control hints run down the sides of the display. The device rests against a dark, plain background.