flows::launch has no unit pin on the liveness ask #434

Question

flows::launch has zero unit coverage of whether run_dotfiles asks devpod
for liveness. Give it some.

The evidence is a measurement, not a suspicion. While building the liveness pins
(#417), two separate mutations
were applied to production code:

• run_dotfiles's workspace_state call replaced by placement.is_running();
• the full Placement::Creatable arm-split stand-in, with the new arm grouped
  into Naming::Anonymous.

Under both, all 1253 core tests stayed green. Only the dl integration
pins caught either. So the behaviour is pinned exclusively at the binary
boundary, and a refactor inside devlaunch-core can break it with cargo test -p devlaunch-core entirely green.

That is a real gap and it is not the same argument #417 made, which is why it is
its own ticket rather than a rider: #417's three rows are launch-shape
observations at the integration seam, and its author deliberately declined to add
a unit-level pin on the grounds that the integration seam catches the defect
directly. It does. But it is the only thing that does, and the two seams fail
independently.

What is wanted: a run_dotfiles-level pin in flows/launch.rs's own unit tests
that fails when the liveness ask is removed or rerouted. Scope it to the seam
flows/launch.rs already uses for recorded calls; do not reach for a new
harness.

Notes for the builder

• The integration pins land in PR #430
  and are the reference for what the shapes are. Read Pin the launch shapes that had no liveness pin #417 and
  #408 for how the counts were
  established.
• Demonstrate the pin can fail, by the same method: apply one of the two
  mutations above, watch it go red, revert, and report what you saw. Pin the launch shapes that had no liveness pin #417's whole
  finding was a green test sitting on broken code.
• Standing refusals from #393,
  none of which this may reintroduce: no liveness cache, no
  try-the-attach-and-fall-back, no always-up, no Remembered arm.
• Interacts with the arm split
  (#418) and with
  #419. If it is cheaper to
  write this pin after the split lands, say so and get it blocked rather than
  writing a pin you will immediately rewrite.
• Cut from origin/main; use your own worktree. Guards in rust/:
  cargo test --workspace, cargo clippy --locked --all-targets -- -D warnings,
  cargo fmt --check.