fix: make hook mode default, require --mcp for MCP server mode

Remove TTY auto-detection from mode selection. The binary now runs in
hook mode by default and requires an explicit --mcp flag for MCP server
mode, ensuring reliable behavior when invoked as a Claude Code hook
regardless of stdin type.

Update install commands for Claude Desktop and Claude Code MCP to pass
--mcp, and drop the PipeAutoDetect test that covered the removed behavior.

Author: tmsdnl

cmd/datetime-mcp/main.go

@@ -8,7 +8,6 @@ import (
 	"strings"
 	_ "time/tzdata"
 
-	"github.com/tmsdnl/datetime-mcp/internal/detect"
 	"github.com/tmsdnl/datetime-mcp/internal/formats"
 	"github.com/tmsdnl/datetime-mcp/internal/hook"
 	"github.com/tmsdnl/datetime-mcp/internal/install"
@@ -31,7 +30,7 @@ func main() {
 	}
 
 	var (
-		forceMCP   = flag.Bool("mcp", false, "Force MCP server mode (override TTY auto-detection)")
+		mcpMode    = flag.Bool("mcp", false, "Run as MCP server (stdio JSON-RPC)")
 		tz         = flag.String("tz", "", "Override timezone (IANA tz database identifier)")
 		format     = flag.String("format", "", "Output format")
 		formatsDir = flag.String("formats-dir", "", "Format files directory (default: {XDG_CONFIG_HOME}/datetime-mcp/formats/)")
@@ -58,8 +57,8 @@ func main() {
 
 	resolvedDir := resolveFormatsDir(*formatsDir)
 
-	// Mode selection: --mcp flag or non-TTY stdin → MCP server mode.
-	if *forceMCP || !detect.IsTerminal(os.Stdin) {
+	// Mode selection: --mcp flag → MCP server mode, otherwise hook mode.
+	if *mcpMode {
 		if err := mcp.Run(mcp.Config{
 			Timezone:   *tz,
 			FormatsDir: resolvedDir,
@@ -137,8 +136,7 @@ func printHelp(formatsDir string) {
 	}
 
 	fmt.Print(`A date/time provider for Claude Desktop, Claude Code, and Codex.
-Prints the current date/time when run from a terminal, or starts an MCP
-server when stdin is a pipe.
+Prints the current date/time by default, or starts an MCP server with --mcp.
 
 Usage:
   datetime-mcp [flags]
@@ -148,7 +146,7 @@ Subcommands:
   install             Register with supported AI tool integrations
 
 Flags:
-  --mcp               Force MCP server mode (override TTY auto-detection)
+  --mcp               Run as MCP server (stdio JSON-RPC)
   --tz string         Override timezone (IANA tz database identifier).
                       Falls back to TZ env var, then system local timezone.
                       Examples: America/Los_Angeles, Europe/Vilnius, UTC

cmd/datetime-mcp/main_test.go

@@ -191,26 +191,6 @@ func TestMCPMode_ToolCall(t *testing.T) {
 	}
 }
 
-func TestMCPMode_PipeAutoDetect(t *testing.T) {
-	// Without --mcp, piping stdin should auto-detect pipe mode and enter MCP mode.
-	msg := `{"jsonrpc":"2.0","id":1,"method":"ping"}` + "\n"
-	stdout, _, code := run(t, msg) // no --mcp flag, but stdin is a pipe via cmd.Stdin
-	if code != 0 {
-		t.Fatalf("exited with %d", code)
-	}
-	// Should have ping response.
-	scanner := bufio.NewScanner(strings.NewReader(stdout))
-	if !scanner.Scan() {
-		t.Fatal("no response for ping")
-	}
-	var resp map[string]any
-	if err := json.Unmarshal(scanner.Bytes(), &resp); err != nil {
-		t.Fatalf("invalid JSON: %v", err)
-	}
-	if resp["result"] == nil {
-		t.Errorf("ping response missing result: %v", resp)
-	}
-}
 
 func TestMCPMode_SIGTERMShutdown(t *testing.T) {
 	if runtime.GOOS == "windows" {

internal/install/claude_code_mcp.go

@@ -30,15 +30,15 @@ func installClaudeCodeMCP(exePath string, dryRun bool) Result {
 
 	if dryRun {
 		return Result{Target: "Claude Code MCP", Status: StatusAdded, Path: path, DryRun: true,
-			Note: "claude mcp add --scope user datetime " + exePath}
+			Note: "claude mcp add --scope user datetime " + exePath + " --mcp"}
 	}
 
 	// Delegate to claude CLI.
 	if _, err := exec.LookPath("claude"); err != nil {
 		return Result{Target: "Claude Code MCP", Status: StatusError, Path: path,
-			Err: fmt.Errorf("claude CLI not found in PATH — run: claude mcp add --scope user datetime %s", exePath)}
+			Err: fmt.Errorf("claude CLI not found in PATH — run: claude mcp add --scope user datetime %s --mcp", exePath)}
 	}
-	cmd := exec.Command("claude", "mcp", "add", "--scope", "user", "datetime", exePath)
+	cmd := exec.Command("claude", "mcp", "add", "--scope", "user", "datetime", exePath, "--mcp")
 	if out, err := cmd.CombinedOutput(); err != nil {
 		return Result{Target: "Claude Code MCP", Status: StatusError, Path: path,
 			Err: fmt.Errorf("claude mcp add: %w: %s", err, out)}

internal/install/claude_desktop.go

@@ -55,12 +55,12 @@ func installClaudeDesktop(exePath string, dryRun bool) Result {
 	}
 
 	if dryRun {
-		b, _ := json.MarshalIndent(map[string]map[string]string{"datetime": {"command": exePath}}, "", "  ")
+		b, _ := json.MarshalIndent(map[string]any{"datetime": map[string]any{"command": exePath, "args": []string{"--mcp"}}}, "", "  ")
 		return Result{Target: "Claude Desktop", Status: StatusAdded, Path: path, DryRun: true, Snippet: string(b)}
 	}
 
 	// Add the entry.
-	entry, _ := json.Marshal(map[string]string{"command": exePath})
+	entry, _ := json.Marshal(map[string]any{"command": exePath, "args": []string{"--mcp"}})
 	mcpServers["datetime"] = json.RawMessage(entry)
 
 	serialized, err := json.Marshal(mcpServers)