run_dotfiles reads the placement where the placement knows #419

Question

Now that Placement distinguishes "asked and denied" from "nothing asked", make
run_dotfiles read the placement where the placement actually knows. Per
#408; read its resolution first.

run_dotfiles matches exhaustively over the arms, and only Creatable asks
devpod. Everything else reads what the launch already established.

Red first: two counts drop 2 to 1.

• dl <ws> dotfiles — 0.57s off
• dl owner/repo@cold dotfiles — 0.57s off (it makes two status calls today, both denials)
• dl <path> dotfiles — unchanged at 1, because that one call is the
  launch's only liveness observation. This is the case whose absence of a pin
  made the original slice look safe.

State the saving as ~0.57s on those two shapes only. Do not claim a general
launch improvement: the map has been burned twice now by numbers that outran
what was measured.

Notes for the builder

• Blocked on the arm split; do not start before it lands.
• Cut from origin/main; use your own worktree.
• Guards in rust/: cargo test --workspace, cargo clippy --locked --all-targets -- -D warnings,
  cargo fmt --check.
• Refusals inherited from The pre-up devpod status call costs 0.43-0.74s on every launch #393: no cache, no try-and-fall-back, no always-up,
  no Remembered.