Bootstrap was separate from all project commands.

Pre-existing image:
  rust:1.90.0-bookworm (local image ID 3914072ca0c3)

Initial isolated probe:
  rustc and Cargo were 1.90.0, but rustfmt and Clippy were absent. With
  --network none the toolchain attempted a channel lookup and failed before project tests.

One-time network-enabled bootstrap:
  rustup component add rustfmt clippy
  docker commit -> hippocamp-rust:1.90-task3

Local runner image ID:
  sha256:2ee1c0cc268a3bc8b6a8a584539662db80498f451210e94e6755da65b5c4f2f5

All subsequent project commands used:
  --network none
  RUSTUP_TOOLCHAIN=1.90.0
