diff --git a/commands_test.go b/commands_test.go
index dce5c94..0d79cbb 100644
--- a/commands_test.go
+++ b/commands_test.go
@@ -121,6 +121,26 @@ func TestExpand(t *testing.T) {
 	}
 }
 
+func TestToCommandsThreadsArgsToDeepDescendants(t *testing.T) {
+	descriptors := []*commandDescriptor{
+		{Name: "a", Commands: []*commandDescriptor{
+			{Name: "b", Commands: []*commandDescriptor{
+				{Name: "c", Commands: []*commandDescriptor{
+					{Name: "d1"},
+					{Name: "d2"},
+				}},
+			}},
+		}},
+	}
+	parent := &executableCommand{path: "/tool", name: "tool"}
+
+	cmds := toCommands(parent, descriptors, nil, &discoverer{maxDepth: -1})
+
+	c := cmds.Find("a").(*executableCommand).cmds.Find("b").(*executableCommand).cmds.Find("c").(*executableCommand)
+	assert.Equal(t, []string{"a", "b", "c", "d1"}, c.cmds.Find("d1").(*executableCommand).args)
+	assert.Equal(t, []string{"a", "b", "c", "d2"}, c.cmds.Find("d2").(*executableCommand).args)
+}
+
 func TestExpandWithDepthZeroDoesNotCallSubcommands(t *testing.T) {
 	stub := &stubParent{name: "stub"}
 
diff --git a/contract.go b/contract.go
index 38cc783..6acb45f 100644
--- a/contract.go
+++ b/contract.go
@@ -194,6 +194,11 @@ type commandDescriptor struct {
 	// is not populated; children are represented by Commands above. It is nil for
 	// commands discovered via contracts other than OpenCLI.
 	openCLI *opencli.Command
+
+	// describedBy, when set, indicates that the command can describe its own
+	// subcommands (e.g. by responding to --help-opencli) even though Commands
+	// is empty. toCommands uses it to defer discovery to the command itself.
+	describedBy describeFunc
 }
 
 func readSummaryFromShellScript(cmd *shellScriptCommand) (string, error) {
diff --git a/contract_opencli.go b/contract_opencli.go
index 8837b9d..ddfc7d6 100644
--- a/contract_opencli.go
+++ b/contract_opencli.go
@@ -16,6 +16,11 @@ import (
 //
 // Unlike ExecutableContract, this contract does not require any particular
 // file extension. Any executable file is eligible.
+//
+// A document may describe its subcommands progressively: when a subcommand's
+// entry lists no children but declares the option "--help-opencli", its
+// subcommands are discovered on demand by invoking the subcommand with
+// --help-opencli (e.g. `tool sub --help-opencli`).
 type OpenCLIContract struct{}
 
 // OpenCLIDescriber is implemented by Commands that can describe themselves
@@ -78,7 +83,10 @@ func (c *OpenCLIContract) BuildCommand(path string, info fs.DirEntry, parent Com
 // describeOpenCLI is a describeFunc that invokes --help-opencli
 // and parses the OpenCLI JSON output into a commandDescriptor.
 func describeOpenCLI(cmd *executableCommand) (*commandDescriptor, error) {
-	out, err := cmd.cache.Fetch(cmd, "help-opencli", func() (string, error) {
+	// Subcommands that respond to --help-opencli themselves share the
+	// executable's path, so the cache key must include their arguments.
+	key := strings.Join(append([]string{"help-opencli"}, cmd.args...), " ")
+	out, err := cmd.cache.Fetch(cmd, key, func() (string, error) {
 		return helpOpenCLIRaw(cmd)
 	})
 	if err != nil {
@@ -150,6 +158,19 @@ func opencliToDescriptor(cmd opencli.Command) *commandDescriptor {
 		for i, sub := range cmd.Commands {
 			d.Commands[i] = opencliToDescriptor(sub)
 		}
+	} else if respondsToHelpOpenCLI(cmd) {
+		d.describedBy = describeOpenCLI
 	}
 	return d
 }
+
+// respondsToHelpOpenCLI returns true if the command declares --help-opencli
+// among its options, signaling that it can describe its own subcommands.
+func respondsToHelpOpenCLI(cmd opencli.Command) bool {
+	for _, o := range cmd.Options {
+		if o.Name == "--help-opencli" {
+			return true
+		}
+	}
+	return false
+}
diff --git a/contract_opencli_test.go b/contract_opencli_test.go
index 0cc7bdd..fcd43bc 100644
--- a/contract_opencli_test.go
+++ b/contract_opencli_test.go
@@ -3,6 +3,7 @@ package exoskeleton
 import (
 	"io/fs"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"testing"
 
@@ -88,10 +89,11 @@ func TestOpenCLICommandDiscovery(t *testing.T) {
 	// Subcommands are discovered from OpenCLI output
 	cmds, err := cmd.Subcommands()
 	assert.NoError(t, err)
-	assert.Len(t, cmds, 3)
+	assert.Len(t, cmds, 4)
 	assert.Equal(t, "build", cmds[0].Name())
 	assert.Equal(t, "mod", cmds[1].Name())
 	assert.Equal(t, "hidden-cmd", cmds[2].Name())
+	assert.Equal(t, "google-drive", cmds[3].Name())
 
 	// Nested subcommands
 	modCmds, err := cmds[1].Subcommands()
@@ -147,6 +149,82 @@ func TestOpenCLICommandExposesMetadata(t *testing.T) {
 	assert.Empty(t, node.Commands)
 }
 
+// buildOpenCLITool builds a Command from the opencli-tool fixture.
+func buildOpenCLITool(t *testing.T, d *discoverer) Command {
+	t.Helper()
+	path := filepath.Join(fixtures, "opencli-tool")
+	info, err := os.Lstat(path)
+	assert.NoError(t, err)
+	cmd, err := (&OpenCLIContract{}).BuildCommand(path, fs.FileInfoToDirEntry(info), nil, d)
+	assert.NoError(t, err)
+	return cmd
+}
+
+func TestOpenCLIProgressiveDiscovery(t *testing.T) {
+	execs := 0
+	countingExecutor := func(c *exec.Cmd) error { execs++; return c.Run() }
+	cmd := buildOpenCLITool(t, &discoverer{maxDepth: -1, executor: countingExecutor})
+
+	cmds, err := cmd.Subcommands()
+	assert.NoError(t, err)
+	assert.Equal(t, 1, execs)
+
+	// The root document lists no subcommands for google-drive but declares
+	// that it responds to --help-opencli. Its sigil and summary come from
+	// the root document without executing anything...
+	gd := cmds.Find("google-drive")
+	assert.True(t, HasSubcommands(gd))
+	summary, err := gd.Summary()
+	assert.NoError(t, err)
+	assert.Equal(t, "Work with Google Drive", summary)
+	assert.Equal(t, 1, execs)
+
+	// ...and Subcommands() invokes `opencli-tool google-drive --help-opencli`.
+	gdCmds, err := gd.Subcommands()
+	assert.NoError(t, err)
+	assert.Equal(t, 2, execs)
+	assert.Len(t, gdCmds, 2)
+
+	// Descendants are invoked with the full path of arguments.
+	docs := gdCmds[0].(*executableCommand)
+	assert.Equal(t, []string{cmd.Path(), "google-drive", "docs"}, docs.Command().Args)
+
+	// OpenCLICommand() returns google-drive's own description of itself,
+	// which is richer than its entry in the root document.
+	node, err := gd.(OpenCLIDescriber).OpenCLICommand()
+	assert.NoError(t, err)
+	assert.Equal(t, "Work with files in Google Drive", *node.Description)
+}
+
+func TestOpenCLIProgressiveDiscoveryRespectsMaxDepth(t *testing.T) {
+	cmd := buildOpenCLITool(t, &discoverer{maxDepth: 1, executor: defaultExecutor})
+
+	cmds, err := cmd.Subcommands()
+	assert.NoError(t, err)
+
+	gdCmds, err := cmds.Find("google-drive").Subcommands()
+	assert.NoError(t, err)
+	assert.Empty(t, gdCmds)
+}
+
+func TestOpenCLIProgressiveDiscoveryCacheKeysDoNotCollide(t *testing.T) {
+	cachePath := filepath.Join(t.TempDir(), "cache.json")
+
+	subcommandsOfGoogleDrive := func() Commands {
+		cmd := buildOpenCLITool(t, &discoverer{maxDepth: -1, executor: defaultExecutor, cache: &FileCache{Path: cachePath}})
+		cmds, err := cmd.Subcommands()
+		assert.NoError(t, err)
+		gdCmds, err := cmds.Find("google-drive").Subcommands()
+		assert.NoError(t, err)
+		return gdCmds
+	}
+
+	// The second call reads google-drive's document from the cache; a key
+	// collision would return the root document instead.
+	assert.Len(t, subcommandsOfGoogleDrive(), 2)
+	assert.Len(t, subcommandsOfGoogleDrive(), 2)
+}
+
 func TestOpenCLICommandForNonOpenCLIContract(t *testing.T) {
 	// A command that was not discovered via the OpenCLI contract has no
 	// OpenCLI metadata; its richer fields come from the Command interface.
diff --git a/executable_command.go b/executable_command.go
index 0e74755..403c3b5 100644
--- a/executable_command.go
+++ b/executable_command.go
@@ -82,7 +82,7 @@ func (cmd *executableCommand) Complete(_ *Entrypoint, args, env []string) ([]str
 // The executable is expected to write the summary to standard output and exit
 // successfully.
 func (cmd *executableCommand) Summary() (string, error) {
-	if cmd.discoverer != nil && cmd.cmds == nil {
+	if cmd.summary == nil && cmd.discoverer != nil && cmd.cmds == nil {
 		if err := cmd.discover(); err != nil {
 			return "", err
 		}
@@ -184,7 +184,7 @@ func (cmd *executableCommand) discover() error {
 	cmd.summary = descriptor.Summary
 	cmd.defaultSubcommand = descriptor.DefaultCommand
 	cmd.openCLI = descriptor.openCLI
-	cmd.cmds = toCommands(cmd, descriptor.Commands, nil, cmd.discoverer)
+	cmd.cmds = toCommands(cmd, descriptor.Commands, cmd.args, cmd.discoverer)
 	return nil
 }
 
@@ -195,7 +195,9 @@ func (cmd *executableCommand) discover() error {
 // The returned Command describes only this node. Its Commands field is not
 // populated; walk Subcommands() to describe the command tree.
 func (cmd *executableCommand) OpenCLICommand() (*opencli.Command, error) {
-	if cmd.openCLI == nil && cmd.discoverer != nil && cmd.cmds == nil {
+	// Discover before answering: a command that describes its own subcommands
+	// provides a richer self-description than its entry in its parent's document.
+	if cmd.discoverer != nil && cmd.cmds == nil {
 		if err := cmd.discover(); err != nil {
 			return nil, err
 		}
@@ -210,11 +212,14 @@ func (cmd *executableCommand) OpenCLICommand() (*opencli.Command, error) {
 func toCommands(parent *executableCommand, descriptors []*commandDescriptor, args []string, d DiscoveryContext) Commands {
 	cmds := Commands{}
 	for _, descriptor := range descriptors {
+		// Allocate exactly, so that sibling commands never share a backing array.
+		cmdArgs := append(append(make([]string, 0, len(args)+1), args...), descriptor.Name)
+
 		c := &executableCommand{
 			parent:            parent,
 			discoveredIn:      parent.discoveredIn,
 			path:              parent.path,
-			args:              append(args, descriptor.Name),
+			args:              cmdArgs,
 			name:              descriptor.Name,
 			aliases:           descriptor.Aliases,
 			summary:           descriptor.Summary,
@@ -225,9 +230,16 @@ func toCommands(parent *executableCommand, descriptors []*commandDescriptor, arg
 			contract:          parent.contract,
 		}
 
-		if len(descriptor.Commands) > 0 && d.MaxDepth() != 0 {
-			c.discoverer = d.Next()
-			c.cmds = toCommands(c, descriptor.Commands, append(args, c.name), d.Next())
+		if d.MaxDepth() != 0 {
+			if len(descriptor.Commands) > 0 {
+				c.discoverer = d.Next()
+				c.cmds = toCommands(c, descriptor.Commands, cmdArgs, d.Next())
+			} else if descriptor.describedBy != nil {
+				// The command can describe its own subcommands: defer
+				// discovery until Subcommands() is called.
+				c.discoverer = d.Next()
+				c.describe = descriptor.describedBy
+			}
 		}
 		cmds = append(cmds, c)
 	}
diff --git a/fixtures/opencli-tool b/fixtures/opencli-tool
index 375312e..4313e4a 100755
--- a/fixtures/opencli-tool
+++ b/fixtures/opencli-tool
@@ -1,6 +1,29 @@
 #!/usr/bin/env bash
 # SUMMARY: An OpenCLI tool
 
+if [[ "$1" == "google-drive" && "$2" == "--help-opencli" ]]; then
+  cat << EOF
+{
+  "opencli": "0.1-block.1",
+  "name": "google-drive",
+  "info": {"version": "1.0.0"},
+  "summary": "Work with Google Drive",
+  "description": "Work with files in Google Drive",
+  "commands": [
+    {
+      "name": "docs",
+      "summary": "Work with Google Docs"
+    },
+    {
+      "name": "sheets",
+      "summary": "Work with Google Sheets"
+    }
+  ]
+}
+EOF
+  exit 0
+fi
+
 if [[ "$1" == "--help-opencli" ]]; then
   cat << EOF
 {
@@ -39,6 +62,13 @@ if [[ "$1" == "--help-opencli" ]]; then
       "arguments": [
         {"name": "file"}
       ]
+    },
+    {
+      "name": "google-drive",
+      "summary": "Work with Google Drive",
+      "options": [
+        {"name": "--help-opencli", "hidden": true}
+      ]
     }
   ]
 }