smoke: five more scenarios + fix exit-code propagation bug the new ones caught

Five new smoke scenarios layered on top of the existing bare + workspace
vm-run tests:

  - exit-code propagation: `sh -c 'exit 42'` must rc=42
  - workspace dry-run: --dry-run lists tracked files without a VM
  - workspace --include-untracked: opt-in ships files outside the git
    index (regression guard on the security-default flip from review 4)
  - concurrent vm runs: two --rm invocations in parallel both succeed
    (stresses per-VM locks, createVMMu reservation window, tap pool)
  - invalid spec rejection: --vcpu 0 must fail with no VM row left
    behind (the "cleanup on partial failure" path the review flagged)

The exit-code scenario caught a real bug on first run:

  `banger vm run --rm -- sh -c 'exit 42'` returned rc=0, not 42.

Root cause in internal/cli/ssh.go's sshCommandArgs: extra args were
appended to the ssh argv verbatim, relying on ssh(1)'s implicit
space-join to deliver the remote command. That works for single
tokens (echo hello) but re-tokenises multi-word commands on the
remote side: `ssh host sh -c 'exit 42'` becomes remote
`sh -c exit 42`, where `42` is $0 for the already-completed `exit`,
and the exit code the user asked for is lost.

Fix: shell-quote every element of extra (`'sh'` `'-c'` `'exit 42'`)
and join them into a single trailing argv entry. ssh's space-join
then produces exactly the command the user typed on the remote
shell. TestSSHCommandArgs was updated to pin the quoting; the
existing TestRunVMRunCommandModePropagatesExitCode test needed a
one-word quote tweak (`false` → `'false'`).

Smoke run after fix passes all seven scenarios in ~2 min on warm
state. cmd/banger coverage jumped to 100% (the invalid-spec
scenario hits the error-reporting path that wasn't covered
before).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/cli/cli_test.go

@@ -1037,7 +1037,6 @@ func TestSSHCommandArgs(t *testing.T) {
 		"-o", "PasswordAuthentication=no",
 		"-o", "KbdInteractiveAuthentication=no",
 		"root@172.16.0.2",
-		"--", "uname", "-a",
 	}
 	for _, s := range wantSubstrings {
 		found := false
@@ -1052,6 +1051,15 @@ func TestSSHCommandArgs(t *testing.T) {
 		}
 	}
 
+	// The trailing argument is the user's command, shell-quoted and
+	// joined so ssh(1)'s space-concatenation produces the exact argv
+	// the user typed on the remote shell. Without this, multi-word
+	// args like `sh -c 'exit 42'` re-tokenise on the remote and lose
+	// exit codes.
+	if got, want := args[len(args)-1], `'--' 'uname' '-a'`; got != want {
+		t.Errorf("trailing arg = %q, want %q (ssh needs a single shell-quoted string)", got, want)
+	}
+
 	// Host-key verification posture: accept-new + a real path into
 	// banger state, not /dev/null.
 	joined := strings.Join(args, " ")
@@ -1607,8 +1615,8 @@ func TestRunVMRunCommandModePropagatesExitCode(t *testing.T) {
 	if !errors.As(err, &exitErr) || exitErr.Code != 7 {
 		t.Fatalf("d.runVMRun error = %v, want ExitCodeError{7}", err)
 	}
-	if len(sshArgsSeen) == 0 || sshArgsSeen[len(sshArgsSeen)-1] != "false" {
-		t.Fatalf("sshArgsSeen = %v, want trailing command 'false'", sshArgsSeen)
+	if len(sshArgsSeen) == 0 || sshArgsSeen[len(sshArgsSeen)-1] != "'false'" {
+		t.Fatalf("sshArgsSeen = %v, want trailing shell-quoted command 'false'", sshArgsSeen)
 	}
 	if !strings.Contains(stderr.String(), "[vm run] running command in guest") {
 		t.Fatalf("stderr = %q, want command progress", stderr.String())

internal/cli/ssh.go

@@ -91,7 +91,20 @@ func sshCommandArgs(cfg model.DaemonConfig, guestIP string, extra []string) ([]s
 		)
 	}
 	args = append(args, "root@"+guestIP)
-	args = append(args, extra...)
+	// ssh(1) concatenates every argument after the host with spaces
+	// before sending to the remote shell. That means passing extra
+	// args raw — `ssh host sh -c 'exit 42'` — re-tokenises on the
+	// remote side to `sh -c exit 42`, where `42` is $0 for the
+	// already-completed `exit`, and the rc the user asked for is
+	// lost. Shell-quote each element and join them ourselves so the
+	// remote shell sees exactly the argv the user typed locally.
+	if len(extra) > 0 {
+		quoted := make([]string, len(extra))
+		for i, a := range extra {
+			quoted[i] = shellQuote(a)
+		}
+		args = append(args, strings.Join(quoted, " "))
+	}
 	return args, nil
 }