2 files changed, 101 insertions, 12 deletions
diff --git a/cmd/hexai-tmux-action/main.go b/cmd/hexai-tmux-action/main.go
index a0f240b..e2f50eb 100644
--- a/cmd/hexai-tmux-action/main.go
+++ b/cmd/hexai-tmux-action/main.go
@@ -16,26 +16,38 @@ import (
 // the real tmux action.
 var runCommand = hexaiaction.RunCommand
 
-func main() {
-	infile := flag.String("infile", "", "Read input from this file instead of stdin")
-	outfile := flag.String("outfile", "", "Write output to this file instead of stdout")
-	uiChild := flag.Bool("ui-child", false, "INTERNAL: run interactive UI and write to -outfile atomically")
+func main() { os.Exit(runMain(os.Args[1:], os.Stdin, os.Stdout, os.Stderr)) }
+
+// runMain parses command-line flags from args, builds actionOptions, and
+// delegates to run. It returns the process exit code: 2 for flag-parse
+// errors (matching stdlib `flag.ExitOnError`), 1 for runtime failures, 0 on
+// success. Splitting the body out of main keeps it testable without
+// touching package-level flag state.
+func runMain(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("hexai-tmux-action", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	infile := fs.String("infile", "", "Read input from this file instead of stdin")
+	outfile := fs.String("outfile", "", "Write output to this file instead of stdout")
+	uiChild := fs.Bool("ui-child", false, "INTERNAL: run interactive UI and write to -outfile atomically")
 	defaultPath := appconfig.DefaultConfigPath()
-	configPath := flag.String("config", "", fmt.Sprintf("path to config file (default: %s)", defaultPath))
-	tmuxTarget := flag.String("tmux-target", "", "tmux popup target pane (advanced)")
-	tmuxPopupWidth := flag.String("tmux-popup-width", "60%", "tmux popup width, e.g. 60% or 120")
-	tmuxPopupHeight := flag.String("tmux-popup-height", "50%", "tmux popup height, e.g. 50% or 30")
-	flag.Parse()
+	configPath := fs.String("config", "", fmt.Sprintf("path to config file (default: %s)", defaultPath))
+	tmuxTarget := fs.String("tmux-target", "", "tmux popup target pane (advanced)")
+	tmuxPopupWidth := fs.String("tmux-popup-width", "60%", "tmux popup width, e.g. 60% or 120")
+	tmuxPopupHeight := fs.String("tmux-popup-height", "50%", "tmux popup height, e.g. 50% or 30")
+	if err := fs.Parse(args); err != nil {
+		return 2
+	}
 
 	opts := actionOptions{
 		infile: *infile, outfile: *outfile,
 		uiChild: *uiChild, configPath: *configPath,
 		tmuxTarget: *tmuxTarget, tmuxPopupWidth: *tmuxPopupWidth, tmuxPopupHeight: *tmuxPopupHeight,
 	}
-	if err := run(opts, os.Stdin, os.Stdout, os.Stderr); err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
+	if err := run(opts, stdin, stdout, stderr); err != nil {
+		fmt.Fprintln(stderr, err)
+		return 1
 	}
+	return 0
 }
 
 // actionOptions holds the parsed command-line flags for hexai-tmux-action.
diff --git a/cmd/hexai-tmux-action/main_test.go b/cmd/hexai-tmux-action/main_test.go
index c2cc95f..e1c02e1 100644
--- a/cmd/hexai-tmux-action/main_test.go
+++ b/cmd/hexai-tmux-action/main_test.go
@@ -1,9 +1,11 @@
 package main
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"io"
+	"strings"
 	"testing"
 
 	"codeberg.org/snonux/hexai/internal/hexaiaction"
@@ -61,3 +63,78 @@ func TestRun_Error(t *testing.T) {
 		t.Fatalf("expected error, got: %v", err)
 	}
 }
+
+// runMain happy path: every flag is forwarded into hexaiaction.Options and
+// the stub returns 0. The captured Options confirm the field-by-field
+// mapping that main relies on.
+func TestRunMain_FlagsForwardedToHexaiaction(t *testing.T) {
+	old := runCommand
+	t.Cleanup(func() { runCommand = old })
+
+	var got hexaiaction.Options
+	runCommand = func(_ context.Context, opts hexaiaction.Options, _ io.Reader, _, _ io.Writer) error {
+		got = opts
+		return nil
+	}
+
+	args := []string{
+		"-infile", "in.txt",
+		"-outfile", "out.txt",
+		"-tmux-target", "%2",
+		"-tmux-popup-width", "70%",
+		"-tmux-popup-height", "40%",
+		"-ui-child",
+	}
+	var stderr bytes.Buffer
+	code := runMain(args, nil, &bytes.Buffer{}, &stderr)
+	if code != 0 {
+		t.Fatalf("runMain code = %d, want 0; stderr=%q", code, stderr.String())
+	}
+	if got.Infile != "in.txt" || got.Outfile != "out.txt" {
+		t.Fatalf("infile/outfile mismatch: %+v", got)
+	}
+	if got.TmuxTarget != "%2" || got.TmuxPopupWidth != "70%" || got.TmuxPopupHeight != "40%" {
+		t.Fatalf("tmux flags mismatch: %+v", got)
+	}
+	if !got.UIChild {
+		t.Fatal("expected UIChild=true")
+	}
+}
+
+// On runCommand failure, runMain returns 1 (the production exit code) and
+// writes the error message to stderr so users see what went wrong.
+func TestRunMain_RuntimeErrorReturnsOne(t *testing.T) {
+	old := runCommand
+	t.Cleanup(func() { runCommand = old })
+	runCommand = func(context.Context, hexaiaction.Options, io.Reader, io.Writer, io.Writer) error {
+		return errors.New("action exploded")
+	}
+
+	var stderr bytes.Buffer
+	code := runMain(nil, nil, &bytes.Buffer{}, &stderr)
+	if code != 1 {
+		t.Fatalf("runMain code = %d, want 1", code)
+	}
+	if !strings.Contains(stderr.String(), "action exploded") {
+		t.Fatalf("stderr missing error: %q", stderr.String())
+	}
+}
+
+// Bad flag must yield exit 2 without ever invoking runCommand.
+func TestRunMain_BadFlagReturnsTwo(t *testing.T) {
+	old := runCommand
+	t.Cleanup(func() { runCommand = old })
+	called := false
+	runCommand = func(context.Context, hexaiaction.Options, io.Reader, io.Writer, io.Writer) error {
+		called = true
+		return nil
+	}
+	var stderr bytes.Buffer
+	code := runMain([]string{"--bogus"}, nil, &bytes.Buffer{}, &stderr)
+	if code != 2 {
+		t.Fatalf("runMain code = %d, want 2", code)
+	}
+	if called {
+		t.Fatal("runCommand must not be called on flag-parse failure")
+	}
+}