feat(hyperguild): subcommand router skeleton

Lays down the cmd/hyperguild/ entry point. Defines the subcommand
contract (ctx, args, stdin, stdout, stderr) error, the dispatch()
function that's testable without os.Exit, and stubs for tier / brain /
mode that return errNotImplemented. Subsequent commits replace each
stub.

Part of Plan 4 (hyperguild CLI) of the hyperguild migration.

cmd/hyperguild/main.go

@@ -0,0 +1,79 @@
+// Package main implements the hyperguild CLI: tier probe, brain HTTP REST
+// access, and .mcp.json mode bootstrap. See docs/superpowers/specs/.
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+)
+
+// subcommand is the contract every hyperguild subcommand satisfies.
+// Functions take an explicit context, args (without the subcommand name
+// itself), and explicit IO so tests can exercise full flows without
+// touching os.Stdin / os.Stdout / os.Exit.
+type subcommand func(ctx context.Context, args []string, stdin io.Reader, stdout, stderr io.Writer) error
+
+// errNotImplemented is returned by stub subcommands until their task lands.
+var errNotImplemented = errors.New("not implemented")
+
+func notYet(ctx context.Context, args []string, stdin io.Reader, stdout, stderr io.Writer) error {
+	return errNotImplemented
+}
+
+func subcommands() map[string]subcommand {
+	return map[string]subcommand{
+		"tier":  notYet,
+		"brain": notYet,
+		"mode":  notYet,
+	}
+}
+
+const usage = `Usage: hyperguild <subcommand> [options]
+
+Subcommands:
+  tier              Probe Anthropic + LiteLLM, print current operating tier.
+  brain query <q>   BM25 search the brain (HTTP REST).
+  brain write <t> <s>
+                    Write stdin as a knowledge entry of type <t>, slug <s>.
+  mode <name>       Bootstrap .mcp.json for a chosen mode:
+                    cloud | client-local | sovereign
+
+Environment:
+  BRAIN_URL              Brain HTTP REST + MCP base URL.
+                         Default: http://koala:30330
+  ANTHROPIC_PROBE_URL    Tier probe URL for the Anthropic API.
+                         Default: https://api.anthropic.com
+  LITELLM_BASE_URL       Tier probe URL for the LiteLLM gateway.
+                         Required for tier probe; no default.
+`
+
+// dispatch routes args to a subcommand and returns the process exit code.
+// Split from main() so tests can drive it without process exit.
+func dispatch(ctx context.Context, args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	if len(args) == 0 {
+		fmt.Fprint(stderr, usage) //nolint:errcheck
+		return 2
+	}
+	switch args[0] {
+	case "-h", "--help", "help":
+		fmt.Fprint(stdout, usage) //nolint:errcheck
+		return 0
+	}
+	cmd, ok := subcommands()[args[0]]
+	if !ok {
+		fmt.Fprintf(stderr, "hyperguild: unknown subcommand: %s\n%s", args[0], usage) //nolint:errcheck
+		return 2
+	}
+	if err := cmd(ctx, args[1:], stdin, stdout, stderr); err != nil {
+		fmt.Fprintf(stderr, "hyperguild %s: %v\n", args[0], err) //nolint:errcheck
+		return 1
+	}
+	return 0
+}
+
+func main() {
+	os.Exit(dispatch(context.Background(), os.Args[1:], os.Stdin, os.Stdout, os.Stderr))
+}

cmd/hyperguild/main_test.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDispatch_Help_PrintsUsageAndReturnsZero(t *testing.T) {
+	var out, errBuf bytes.Buffer
+	code := dispatch(context.Background(), []string{"--help"}, strings.NewReader(""), &out, &errBuf)
+	assert.Equal(t, 0, code)
+	assert.Contains(t, out.String(), "Usage: hyperguild")
+	assert.Contains(t, out.String(), "tier")
+	assert.Contains(t, out.String(), "brain")
+	assert.Contains(t, out.String(), "mode")
+}
+
+func TestDispatch_NoArgs_PrintsUsageAndReturnsTwo(t *testing.T) {
+	var out, errBuf bytes.Buffer
+	code := dispatch(context.Background(), []string{}, strings.NewReader(""), &out, &errBuf)
+	assert.Equal(t, 2, code)
+	assert.Contains(t, errBuf.String(), "Usage: hyperguild")
+}
+
+func TestDispatch_UnknownSubcommand_ReturnsTwo(t *testing.T) {
+	var out, errBuf bytes.Buffer
+	code := dispatch(context.Background(), []string{"bogus"}, strings.NewReader(""), &out, &errBuf)
+	assert.Equal(t, 2, code)
+	assert.Contains(t, errBuf.String(), "unknown subcommand: bogus")
+}
+
+func TestDispatch_KnownSubcommand_RoutesAndReturnsExitCode(t *testing.T) {
+	var out, errBuf bytes.Buffer
+	code := dispatch(context.Background(), []string{"tier"}, strings.NewReader(""), &out, &errBuf)
+	// At Task 1 time, tier returns the not-implemented error → exit 1.
+	assert.Equal(t, 1, code)
+	assert.Contains(t, errBuf.String(), "not implemented")
+}