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>

scripts/smoke.sh

@@ -107,6 +107,75 @@ log "workspace vm run: create + start + workspace prepare + cat guest file + --r
 ws_out="$("$BANGER" vm run --rm "$repodir" -- cat /root/repo/smoke-file.txt)" || die "workspace vm run exit $?"
 grep -q 'smoke-workspace-marker' <<<"$ws_out" || die "workspace vm run didn't ship smoke-file.txt: $ws_out"
 
+# --- command exit-code propagation ------------------------------------
+# A non-zero exit from the guest command must surface as banger's own
+# exit code. Regressions here are hard to catch any other way — the
+# local Go tests don't cross the SSH boundary, and users expect their
+# CI scripts that wrap `banger vm run` to fail when the thing inside
+# the VM failed.
+log 'exit-code propagation: guest `sh -c "exit 42"` must produce rc=42'
+set +e
+"$BANGER" vm run --rm -- sh -c 'exit 42'
+rc=$?
+set -e
+[[ "$rc" -eq 42 ]] || die "exit-code propagation: got rc=$rc, want 42"
+
+# --- workspace dry-run (no VM) ----------------------------------------
+# Pure CLI-side path — no VM, no sudo, just the local git inspection
+# against d.repoInspector. Fast; catches regressions in the preview
+# output (file list shape, mode line) that the Go tests already pin
+# but that could still be broken by a client-side wiring change.
+log 'workspace dry-run: list tracked files without creating a VM'
+dry_out="$("$BANGER" vm run --dry-run "$repodir")" || die "dry-run exit $?"
+grep -q 'smoke-file.txt' <<<"$dry_out" || die "dry-run didn't list smoke-file.txt: $dry_out"
+grep -q 'mode: tracked only' <<<"$dry_out" || die "dry-run mode line missing or wrong: $dry_out"
+
+# --- workspace --include-untracked -----------------------------------
+# The default is tracked-only (review cycle 4). Opt-in must ship
+# untracked files too. Write one, run with --include-untracked, verify
+# it reaches the guest.
+log 'workspace --include-untracked: opt-in ships files outside the git index'
+echo 'untracked-marker' > "$repodir/smoke-untracked.txt"
+inc_out="$("$BANGER" vm run --rm --include-untracked "$repodir" -- cat /root/repo/smoke-untracked.txt)" || die "include-untracked vm run exit $?"
+grep -q 'untracked-marker' <<<"$inc_out" || die "--include-untracked didn't ship the untracked file: $inc_out"
+# Restore repo to tracked-only state for any later scenarios.
+rm -f "$repodir/smoke-untracked.txt"
+
+# --- concurrent vm runs -----------------------------------------------
+# Stresses per-VM lock scoping, the tap pool warm-up path, and
+# createVMMu's narrow reservation window. Two `vm run --rm` invocations
+# that actually overlap should both succeed. A regression that
+# serialises create path too aggressively would make this slow but
+# still pass; a regression that breaks tap allocation or name
+# uniqueness would fail one of them.
+log 'concurrent vm runs: two --rm invocations must both succeed'
+tmpA="$runtime_dir/concurrent-a.out"
+tmpB="$runtime_dir/concurrent-b.out"
+"$BANGER" vm run --rm -- echo smoke-concurrent-a > "$tmpA" 2>&1 &
+pidA=$!
+"$BANGER" vm run --rm -- echo smoke-concurrent-b > "$tmpB" 2>&1 &
+pidB=$!
+wait "$pidA" || die "concurrent VM A exited non-zero: $(cat "$tmpA")"
+wait "$pidB" || die "concurrent VM B exited non-zero: $(cat "$tmpB")"
+grep -q 'smoke-concurrent-a' "$tmpA" || die "concurrent VM A missing marker: $(cat "$tmpA")"
+grep -q 'smoke-concurrent-b' "$tmpB" || die "concurrent VM B missing marker: $(cat "$tmpB")"
+
+# --- invalid spec rejection + no artifact leak ------------------------
+# Tests the negative-path create flow: a blatantly invalid VM spec
+# must fail before any VM row is persisted. The review cycle flagged
+# "cleanup on partial failure" as under-tested; this scenario pins
+# that a rejected create doesn't leak a reservation we then have to
+# clean up by hand.
+log 'invalid spec rejection: --vcpu 0 must fail and leave no VM behind'
+pre_vms="$("$BANGER" vm list --all 2>/dev/null | wc -l)"
+set +e
+"$BANGER" vm run --rm --vcpu 0 -- echo unused >/dev/null 2>&1
+rc=$?
+set -e
+[[ "$rc" -ne 0 ]] || die 'invalid spec: vm run succeeded despite --vcpu 0'
+post_vms="$("$BANGER" vm list --all 2>/dev/null | wc -l)"
+[[ "$pre_vms" == "$post_vms" ]] || die "invalid spec leaked a VM row: pre=$pre_vms, post=$post_vms"
+
 # --- daemon stop (flushes coverage) -----------------------------------
 log 'stopping daemon so instrumented binaries flush coverage'
 "$BANGER" daemon stop >/dev/null 2>&1 || true