diff --git a/.gitignore b/.gitignore
index 8ad215f6..4cf82df2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -70,3 +70,4 @@ CLAUDE.md
 # Added by ggshield
 .cache_ggshield
 specs/*/review-transcript.jsonl
+specs/*/review-transcript.jsonl.stderr
diff --git a/cli/internal/cmd/spec.go b/cli/internal/cmd/spec.go
index fd790309..3327bdad 100644
--- a/cli/internal/cmd/spec.go
+++ b/cli/internal/cmd/spec.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -38,6 +39,15 @@ var lookPath = exec.LookPath
 
 // runCommand is a seam for the launch itself, so the command's wiring is
 // testable without spawning a reviewer that would take half an hour.
+// sessionAlive reports whether a detached tmux session still exists, and
+// sleepFor paces the probe. Both are seams so tests can simulate a launch that
+// died without needing tmux or real time.
+var sessionAlive = func(session string) bool {
+	return exec.Command("tmux", "has-session", "-t", session).Run() == nil
+}
+
+var sleepFor = time.Sleep
+
 var runCommand = func(dir string, argv []string) error {
 	c := exec.Command(argv[0], argv[1:]...)
 	c.Dir = dir
@@ -192,6 +202,9 @@ is the only record of how.`,
 				if err := runCommand(repoRoot, launch); err != nil {
 					return fmt.Errorf("starting the tmux session: %w", err)
 				}
+				if err := confirmLaunched(session, transcript); err != nil {
+					return err
+				}
 				cmd.Printf("[OK] Review running detached. Watch it with:\n\n    tmux attach -t %s\n\n", session)
 				cmd.Printf("When it finishes, %s carries the verdict and archive reads it.\n", spec.ReviewFile)
 				return nil
@@ -210,6 +223,63 @@ is the only record of how.`,
 	return cmd
 }
 
+// confirmLaunched turns "the session was created" into "the reviewer survived
+// startup" — two claims the launcher used to conflate (#989).
+//
+// `tmux new-session -d` exits 0 the moment the session exists; the process
+// inside it can be dead a fraction of a second later. Measured on the failure
+// that prompted this: the session lasted 0.54s and the launcher reported a
+// running review over a 0-byte transcript, so the archive gate's much later
+// "no review.md" read as "you forgot to run it" rather than "it died".
+//
+// The window is deliberately modest. It proves the reviewer got past startup,
+// which is where a bad credential, a missing binary or an unreachable model all
+// fail; it does NOT promise the run will finish. A death at minute three is
+// inherently unwatched in detached mode, and `spec archive` refusing without a
+// review.md stays the backstop for that.
+func confirmLaunched(session, transcript string) error {
+	const (
+		window = 3 * time.Second        // ~6x the slowest observed startup failure
+		step   = 250 * time.Millisecond // cheap enough to poll, coarse enough not to spin
+	)
+	for waited := time.Duration(0); waited < window; waited += step {
+		sleepFor(step)
+		if sessionAlive(session) {
+			continue
+		}
+		return fmt.Errorf("the review died on startup — tmux session %q is already gone.\n%s\n"+
+			"Nothing was reviewed and %s was not written; re-run with --foreground to watch it fail live",
+			session, reviewerLastWords(transcript), spec.ReviewFile)
+	}
+	return nil
+}
+
+// reviewerLastWords quotes what the dead reviewer actually said. An error that
+// reproduces the output it received beats one that only reports that parsing or
+// launching failed — the original defect discarded the reason entirely, which is
+// why nobody could tell a broken credential from a missing binary.
+func reviewerLastWords(transcript string) string {
+	for _, src := range []struct{ label, path string }{
+		{"stderr", spec.StderrPath(transcript)},
+		{"transcript", transcript},
+	} {
+		b, err := os.ReadFile(src.path)
+		if err != nil {
+			continue
+		}
+		out := strings.TrimSpace(string(b))
+		if out == "" {
+			continue
+		}
+		const max = 800
+		if len(out) > max {
+			out = out[:max] + fmt.Sprintf("\n… (truncated; full %s at %s)", src.label, src.path)
+		}
+		return "It wrote, on " + src.label + ":\n" + out
+	}
+	return "It wrote nothing to either the transcript or its stderr, so the failure happened before the reviewer produced output at all."
+}
+
 func newSpecInitCmd() *cobra.Command {
 	var (
 		issueNum     int
diff --git a/cli/internal/cmd/spec_review_test.go b/cli/internal/cmd/spec_review_test.go
index 10a78cf9..24b4142c 100644
--- a/cli/internal/cmd/spec_review_test.go
+++ b/cli/internal/cmd/spec_review_test.go
@@ -4,6 +4,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 	"testing"
 )
 
@@ -100,3 +101,104 @@ func TestSpecReviewRefusesAnUnpooledReviewer(t *testing.T) {
 		t.Errorf("the refusal must list the available reviewers, got: %v", err)
 	}
 }
+
+// --- BUG-081: the launcher must not announce a review it never started -------
+//
+// `tmux new-session -d` returns 0 once the SESSION exists, which says nothing
+// about the process inside it. Observed on HARNESS-072: the reviewer died on a
+// broken credential, the session was gone within half a second, and the
+// launcher printed "[OK] Review running detached" over a 0-byte transcript.
+
+// stubLaunch makes the detached path runnable in a test: tmux "exists", the
+// new-session call "succeeds", and the sleep between liveness probes is free.
+// alive decides whether the session outlives the probe window.
+func stubLaunch(t *testing.T, alive bool) {
+	t.Helper()
+	prevLook, prevRun, prevAlive, prevSleep := lookPath, runCommand, sessionAlive, sleepFor
+	lookPath = func(string) (string, error) { return "/usr/bin/tmux", nil }
+	runCommand = func(string, []string) error { return nil }
+	sessionAlive = func(string) bool { return alive }
+	sleepFor = func(time.Duration) {}
+	t.Cleanup(func() {
+		lookPath, runCommand, sessionAlive, sleepFor = prevLook, prevRun, prevAlive, prevSleep
+	})
+}
+
+func TestSpecReviewFailsWhenTheLaunchDiedImmediately(t *testing.T) {
+	root := makeRepo(t)
+	seedPool(t, root)
+	seedSpec(t, root, "AI-001-x", "---\nstatus: implementing\n---\n# AI-001-x\n")
+	stubLaunch(t, false)
+
+	stdout, stderr, err := execute(t, "spec", "review", "AI-001-x")
+	out := stdout + stderr
+	if err == nil {
+		t.Fatalf("a launch whose session is already gone must fail:\n%s", out)
+	}
+	if strings.Contains(out, "Review running detached") {
+		t.Errorf("announced a running review over a dead one:\n%s", out)
+	}
+}
+
+// The error has to carry what the reviewer said, not just that it died. The
+// death reason arrives on stderr, which the `| tee` pipeline never captured —
+// that is why the original failure left no clue anywhere.
+func TestSpecReviewQuotesTheReviewerStderrWhenItDies(t *testing.T) {
+	root := makeRepo(t)
+	seedPool(t, root)
+	seedSpec(t, root, "AI-001-x", "---\nstatus: implementing\n---\n# AI-001-x\n")
+	stubLaunch(t, false)
+
+	stderrFile := filepath.Join(root, "specs", "AI-001-x", "review-transcript.jsonl.stderr")
+	if err := os.WriteFile(stderrFile, []byte("Error: bw resolve dockerhub/password: not found\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	_, _, err := execute(t, "spec", "review", "AI-001-x")
+	if err == nil {
+		t.Fatal("expected the dead launch to fail")
+	}
+	if !strings.Contains(err.Error(), "bw resolve dockerhub/password") {
+		t.Errorf("the error must quote what the reviewer wrote, got: %v", err)
+	}
+}
+
+func TestSpecReviewAnnouncesALaunchThatSurvived(t *testing.T) {
+	root := makeRepo(t)
+	seedPool(t, root)
+	seedSpec(t, root, "AI-001-x", "---\nstatus: implementing\n---\n# AI-001-x\n")
+	stubLaunch(t, true)
+
+	stdout, stderr, err := execute(t, "spec", "review", "AI-001-x")
+	out := stdout + stderr
+	if err != nil {
+		t.Fatalf("a surviving launch must succeed: %v\n%s", err, out)
+	}
+	if !strings.Contains(out, "tmux attach -t review-AI-001-x") {
+		t.Errorf("a surviving launch must still tell the caller how to watch it:\n%s", out)
+	}
+}
+
+// The stderr file is a sibling of the transcript, never merged into it: the
+// transcript is jsonl an auditor parses, and interleaved diagnostics break that.
+func TestSpecReviewRedirectsStderrBesideTheTranscript(t *testing.T) {
+	root := makeRepo(t)
+	seedPool(t, root)
+	seedSpec(t, root, "AI-001-x", "---\nstatus: implementing\n---\n# AI-001-x\n")
+
+	prev := lookPath
+	lookPath = func(string) (string, error) { return "/usr/bin/tmux", nil }
+	t.Cleanup(func() { lookPath = prev })
+
+	stdout, stderr, err := execute(t, "spec", "review", "AI-001-x", "--dry-run")
+	if err != nil {
+		t.Fatalf("spec review --dry-run: %v", err)
+	}
+	out := stdout + stderr
+	if !strings.Contains(out, "review-transcript.jsonl.stderr") {
+		t.Errorf("stderr must be captured to its own file:\n%s", out)
+	}
+	if strings.Contains(out, "2>&1") {
+		t.Errorf("stderr must not be folded into the transcript pipe:\n%s", out)
+	}
+}
diff --git a/cli/internal/spec/review_launch.go b/cli/internal/spec/review_launch.go
index 95aad00d..805b4de5 100644
--- a/cli/internal/spec/review_launch.go
+++ b/cli/internal/spec/review_launch.go
@@ -156,6 +156,16 @@ func TranscriptPath(repoRoot, specID string) string {
 	return filepath.Join(repoRoot, "specs", specID, TranscriptFile)
 }
 
+// StderrPath is where the launched reviewer's stderr lands, beside the
+// transcript rather than inside it: the transcript is machine-readable jsonl an
+// auditor parses, and interleaving diagnostics into it would corrupt that.
+//
+// It exists because the death reason used to have nowhere to go. TmuxWrap pipes
+// the reviewer through `tee`, which carries stdout only, so a reviewer that died
+// on startup wrote its error to a pane that vanished with the session — leaving
+// a 0-byte transcript and no clue (#989).
+func StderrPath(transcript string) string { return transcript + ".stderr" }
+
 // ResolveReviewer picks which pool member runs.
 //
 // Default is the pool's FIRST entry — the launcher's primary. An explicit want
@@ -279,6 +289,8 @@ func TmuxWrap(session, dir string, argv []string, transcript string) []string {
 		"tmux", "new-session", "-d",
 		"-s", session,
 		"-c", dir,
-		ShellJoin(argv) + " | tee " + shellQuote(transcript),
+		ShellJoin(argv) +
+			" 2> " + shellQuote(StderrPath(transcript)) +
+			" | tee " + shellQuote(transcript),
 	}
 }