fix(microvm): the third place that assumed a VM phase has a repository

The research-vm scenario failed on its first run, and said exactly why:

  mission has no checkout at /var/lib/clawmates-missions/<id>/repo
    — a microvm phase needs a repository

`phase_runner` refuses upstream of both places the last commit fixed. Three
guards, written independently, all encoding "a microVM phase implies a git
checkout" — which is why the capture filter could cite it as settled fact.

A repo-BACKED mission with no checkout is still a real fault and still refused;
booting a VM to hand the agent an empty directory would turn a setup failure
into a confusing agent report. A repo-LESS one now gets the empty workspace
made here, so the executor's inject has something to pack.

Co-Authored-By: Claude Opus 5 <[email protected]>

crates/cm-api/src/phase_runner.rs

@@ -1148,15 +1148,27 @@ async fn launch_microvm_phase(
                  /dev/kvm"
                     .to_string()
             })?;
-            if !repo.is_dir() {
+            // A repo-BACKED mission with no checkout is a real fault: something
-                // A research-only mission has no checkout, and there is nothing
+            // went wrong before the phase, and booting a VM to hand the agent an
-                // for a VM to work on. Better to say so than to boot one and hand
+            // empty directory would turn it into a confusing agent report.
-                // the agent an empty directory.
+            //
+            // A repo-LESS mission is a different thing entirely, and this guard
+            // used to refuse it too — "a microvm phase needs a repository" was
+            // the third of three places that assumed so, alongside the inject
+            // and the readiness probe. It gets an empty workspace instead, made
+            // here so the executor's inject has something to pack.
+            if has_repo && !repo.is_dir() {
                 return Err(format!(
-                    "mission has no checkout at {} — a microvm phase needs a repository",
+                    "mission has no checkout at {} — a repo-backed microvm phase \
+                     needs one",
                     repo.display()
                 ));
             }
+            if !has_repo {
+                std::fs::create_dir_all(&repo).map_err(|e| {
+                    format!("create empty workspace {}: {e}", repo.display())
+                })?;
+            }
             crate::microvm_executor::run_phase_in_vm(
                 &hub,
                 crate::microvm_executor::VmPhase {