diff --git a/internal/cmd/account.go b/internal/cmd/account.go
index 07882b4d..5a75833d 100644
--- a/internal/cmd/account.go
+++ b/internal/cmd/account.go
@@ -24,6 +24,7 @@ var accountCmd = &cobra.Command{
 	Use:     "account",
 	GroupID: GroupConfig,
 	Short:   "Manage Claude Code accounts",
+	RunE:    requireSubcommand,
 	Long: `Manage multiple Claude Code accounts for Gas Town.
 
 This enables switching between accounts (e.g., personal vs work) with
diff --git a/internal/cmd/convoy.go b/internal/cmd/convoy.go
index 5c541e61..57e33f8e 100644
--- a/internal/cmd/convoy.go
+++ b/internal/cmd/convoy.go
@@ -37,6 +37,7 @@ var convoyCmd = &cobra.Command{
 	Use:     "convoy",
 	GroupID: GroupWork,
 	Short:   "Track batches of work across rigs",
+	RunE:    requireSubcommand,
 	Long: `Manage convoys - the primary unit for tracking batched work.
 
 A convoy is a persistent tracking unit that monitors related issues across
diff --git a/internal/cmd/crew.go b/internal/cmd/crew.go
index 1fac5491..0d9f4761 100644
--- a/internal/cmd/crew.go
+++ b/internal/cmd/crew.go
@@ -24,6 +24,7 @@ var crewCmd = &cobra.Command{
 	Use:     "crew",
 	GroupID: GroupWorkspace,
 	Short:   "Manage crew workspaces (user-managed persistent workspaces)",
+	RunE:    requireSubcommand,
 	Long: `Crew workers are user-managed persistent workspaces within a rig.
 
 Unlike polecats which are witness-managed and transient, crew workers are:
diff --git a/internal/cmd/daemon.go b/internal/cmd/daemon.go
index 7cdcedb3..175cbf5b 100644
--- a/internal/cmd/daemon.go
+++ b/internal/cmd/daemon.go
@@ -17,6 +17,7 @@ var daemonCmd = &cobra.Command{
 	Use:     "daemon",
 	GroupID: GroupServices,
 	Short:   "Manage the Gas Town daemon",
+	RunE:    requireSubcommand,
 	Long: `Manage the Gas Town background daemon.
 
 The daemon is a simple Go process that:
diff --git a/internal/cmd/deacon.go b/internal/cmd/deacon.go
index 9c6f0a83..33841d2e 100644
--- a/internal/cmd/deacon.go
+++ b/internal/cmd/deacon.go
@@ -26,6 +26,7 @@ var deaconCmd = &cobra.Command{
 	Aliases: []string{"dea"},
 	GroupID: GroupAgents,
 	Short:   "Manage the Deacon session",
+	RunE:    requireSubcommand,
 	Long: `Manage the Deacon tmux session.
 
 The Deacon is the hierarchical health-check orchestrator for Gas Town.
diff --git a/internal/cmd/mail.go b/internal/cmd/mail.go
index 8b15f12e..773037e0 100644
--- a/internal/cmd/mail.go
+++ b/internal/cmd/mail.go
@@ -46,6 +46,7 @@ var mailCmd = &cobra.Command{
 	Use:     "mail",
 	GroupID: GroupComm,
 	Short:   "Agent messaging system",
+	RunE:    requireSubcommand,
 	Long: `Send and receive messages between agents.
 
 The mail system allows Mayor, polecats, and the Refinery to communicate.
diff --git a/internal/cmd/mayor.go b/internal/cmd/mayor.go
index dff67c82..82557061 100644
--- a/internal/cmd/mayor.go
+++ b/internal/cmd/mayor.go
@@ -21,6 +21,7 @@ var mayorCmd = &cobra.Command{
 	Aliases: []string{"may"},
 	GroupID: GroupAgents,
 	Short:   "Manage the Mayor session",
+	RunE:    requireSubcommand,
 	Long: `Manage the Mayor tmux session.
 
 The Mayor is the global coordinator for Gas Town, running as a persistent
diff --git a/internal/cmd/molecule.go b/internal/cmd/molecule.go
index 2cc40d69..3344e252 100644
--- a/internal/cmd/molecule.go
+++ b/internal/cmd/molecule.go
@@ -14,6 +14,7 @@ var moleculeCmd = &cobra.Command{
 	Aliases: []string{"molecule"},
 	GroupID: GroupWork,
 	Short:   "Agent molecule workflow commands",
+	RunE:    requireSubcommand,
 	Long: `Agent-specific molecule workflow operations.
 
 These commands operate on the current agent's hook and attached molecules.
@@ -204,6 +205,7 @@ a permanent (but compact) record.`,
 var moleculeStepCmd = &cobra.Command{
 	Use:   "step",
 	Short: "Molecule step operations",
+	RunE:  requireSubcommand,
 	Long: `Commands for working with molecule steps.
 
 A molecule is a DAG of steps. Each step is a beads issue with the molecule root
diff --git a/internal/cmd/mq.go b/internal/cmd/mq.go
index 3bd42550..2d97bdce 100644
--- a/internal/cmd/mq.go
+++ b/internal/cmd/mq.go
@@ -53,6 +53,7 @@ var mqCmd = &cobra.Command{
 	Use:     "mq",
 	GroupID: GroupWork,
 	Short:   "Merge queue operations",
+	RunE:    requireSubcommand,
 	Long: `Manage the merge queue for a rig.
 
 The merge queue tracks work branches from polecats waiting to be merged.
@@ -168,6 +169,7 @@ Example:
 var mqIntegrationCmd = &cobra.Command{
 	Use:   "integration",
 	Short: "Manage integration branches for epics",
+	RunE:  requireSubcommand,
 	Long: `Manage integration branches for batch work on epics.
 
 Integration branches allow multiple MRs for an epic to target a shared
diff --git a/internal/cmd/polecat.go b/internal/cmd/polecat.go
index 77f4e580..0ad3f7b3 100644
--- a/internal/cmd/polecat.go
+++ b/internal/cmd/polecat.go
@@ -33,6 +33,7 @@ var polecatCmd = &cobra.Command{
 	Aliases: []string{"cat", "polecats"},
 	GroupID: GroupAgents,
 	Short:   "Manage polecats in rigs",
+	RunE:    requireSubcommand,
 	Long: `Manage polecat lifecycle in rigs.
 
 Polecats are worker agents that operate in their own git worktrees.
diff --git a/internal/cmd/refinery.go b/internal/cmd/refinery.go
index 75d75043..27aeaf63 100644
--- a/internal/cmd/refinery.go
+++ b/internal/cmd/refinery.go
@@ -25,6 +25,7 @@ var refineryCmd = &cobra.Command{
 	Aliases: []string{"ref"},
 	GroupID: GroupAgents,
 	Short:   "Manage the merge queue processor",
+	RunE:    requireSubcommand,
 	Long: `Manage the Refinery merge queue processor for a rig.
 
 The Refinery processes merge requests from polecats, merging their work
diff --git a/internal/cmd/rig.go b/internal/cmd/rig.go
index fb1d68cc..52fd60a1 100644
--- a/internal/cmd/rig.go
+++ b/internal/cmd/rig.go
@@ -26,6 +26,7 @@ var rigCmd = &cobra.Command{
 	Use:     "rig",
 	GroupID: GroupWorkspace,
 	Short:   "Manage rigs in the workspace",
+	RunE:    requireSubcommand,
 	Long: `Manage rigs (project containers) in the Gas Town workspace.
 
 A rig is a container for managing a project and its agents:
diff --git a/internal/cmd/root.go b/internal/cmd/root.go
index 75ae1a11..2a95bdb0 100644
--- a/internal/cmd/root.go
+++ b/internal/cmd/root.go
@@ -2,6 +2,7 @@
 package cmd
 
 import (
+	"fmt"
 	"strings"
 
 	"github.com/spf13/cobra"
@@ -85,3 +86,14 @@ func buildCommandPath(cmd *cobra.Command) string {
 	}
 	return strings.Join(parts, " ")
 }
+
+// requireSubcommand returns a RunE function for parent commands that require
+// a subcommand. Without this, Cobra silently shows help and exits 0 for
+// unknown subcommands like "gt mol foobar", masking errors.
+func requireSubcommand(cmd *cobra.Command, args []string) error {
+	if len(args) == 0 {
+		return fmt.Errorf("requires a subcommand\n\nRun '%s --help' for usage", buildCommandPath(cmd))
+	}
+	return fmt.Errorf("unknown command %q for %q\n\nRun '%s --help' for available commands",
+		args[0], buildCommandPath(cmd), buildCommandPath(cmd))
+}
diff --git a/internal/cmd/session.go b/internal/cmd/session.go
index 79ef57fd..6d7ff4e5 100644
--- a/internal/cmd/session.go
+++ b/internal/cmd/session.go
@@ -37,6 +37,7 @@ var sessionCmd = &cobra.Command{
 	Aliases: []string{"sess"},
 	GroupID: GroupAgents,
 	Short:   "Manage polecat sessions",
+	RunE:    requireSubcommand,
 	Long: `Manage tmux sessions for polecats.
 
 Sessions are tmux sessions running Claude for each polecat.
diff --git a/internal/cmd/swarm.go b/internal/cmd/swarm.go
index 67ca6f48..df92fb50 100644
--- a/internal/cmd/swarm.go
+++ b/internal/cmd/swarm.go
@@ -40,6 +40,7 @@ var swarmCmd = &cobra.Command{
 	GroupID:    GroupWork,
 	Short:      "[DEPRECATED] Use 'gt convoy' instead",
 	Deprecated: "Use 'gt convoy' for work tracking. A 'swarm' is now just the ephemeral workers on a convoy.",
+	RunE:       requireSubcommand,
 	Long: `DEPRECATED: Use 'gt convoy' instead.
 
 The term "swarm" now refers to the ephemeral set of workers on a convoy's issues,
diff --git a/internal/cmd/witness.go b/internal/cmd/witness.go
index bf528c15..34f5df66 100644
--- a/internal/cmd/witness.go
+++ b/internal/cmd/witness.go
@@ -29,6 +29,7 @@ var witnessCmd = &cobra.Command{
 	Use:     "witness",
 	GroupID: GroupAgents,
 	Short:   "Manage the polecat monitoring agent",
+	RunE:    requireSubcommand,
 	Long: `Manage the Witness monitoring agent for a rig.
 
 The Witness monitors polecats for stuck/idle state, nudges polecats