Use \$EDITOR as default editor, falling back to vi (task 344)

defaultConfig() now reads the \$EDITOR environment variable for EditCmd
so users get their preferred editor automatically without touching the
config file. Falls back to "vi" (universally available) when \$EDITOR
is unset or empty. A JSON config value still takes precedence over \$EDITOR.

Updated tests to: unset \$EDITOR where "vi" fallback is asserted, add
TestLoad_editorEnvVar covering the three cases (\$EDITOR unset, \$EDITOR
set, JSON override), and remove all stale "hx" references from comments.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

3 files changed, 50 insertions, 13 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index 4e5a5c8..7e62888 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -41,7 +41,7 @@ Config is read from `~/.config/foostore.json` at startup (merged over defaults).
 - `data_dir`: Git repo where encrypted `.index` / `.data` file pairs are stored (default: `~/git/geheimlager`)
 - `key_file`: Path to the raw encryption key file (default: `~/.geheimlager.key`)
 - `export_dir`: Temporary directory for decrypted exports (default: `~/.geheimlagerexport`)
-- `edit_cmd`: Editor used by the `edit` command (default: `hx`)
+- `edit_cmd`: Editor used by the `edit` command (default: `$EDITOR`, falling back to `vi`)
 - `sync_repos`: List of git remote names to push/pull when syncing
 
 The PIN (entered at startup or via `$PIN` env var) is used to derive the AES IV; the actual key comes from `key_file`.
diff --git a/internal/config/config.go b/internal/config/config.go
index 6354d83..04c8302 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -31,11 +31,20 @@ type Config struct {
 	SyncRepos         []string `json:"sync_repos"`
 }
 
-// defaultConfig returns a Config populated with the same defaults as the
-// Ruby reference implementation's Config::DEFAULTS.  It calls
-// os.UserHomeDir() so that path fields expand correctly at runtime.
+// defaultConfig returns a Config populated with built-in defaults.
+// EditCmd honours the $EDITOR environment variable and falls back to "vi"
+// when the variable is unset or empty, so users get their preferred editor
+// automatically without touching the config file.
+// It calls os.UserHomeDir() so that path fields expand correctly at runtime.
 func defaultConfig() Config {
 	home, _ := os.UserHomeDir()
+
+	// Prefer $EDITOR; fall back to vi if not set.
+	editCmd := os.Getenv("EDITOR")
+	if editCmd == "" {
+		editCmd = "vi"
+	}
+
 	return Config{
 		DataDir:           filepath.Join(home, "git", "geheimlager"),
 		ExportDir:         filepath.Join(home, ".geheimlagerexport"),
@@ -43,7 +52,7 @@ func defaultConfig() Config {
 		KeyLength:         32,
 		EncAlg:            "AES-256-CBC",
 		AddToIV:           "Hello world",
-		EditCmd:           "hx",
+		EditCmd:           editCmd,
 		GnomeClipboardCmd: "gpaste-client",
 		MacOSClipboardCmd: "pbcopy",
 		SyncRepos:         []string{"git1", "git2"},
@@ -68,8 +77,9 @@ func expandPathFields(cfg *Config) {
 	cfg.KeyFile = expandTilde(cfg.KeyFile)
 }
 
-// Load reads ~/.config/geheim.json and merges it over the built-in defaults.
-// Any field present in the JSON file overrides the corresponding default;
+// Load reads ~/.config/foostore.json and merges it over the built-in defaults.
+// Any field present in the JSON file overrides the corresponding default
+// (including edit_cmd, which defaults to $EDITOR or "vi" when unset);
 // fields absent from the file keep their default values.
 // If the file is missing or contains invalid JSON a warning is printed to
 // stderr and the pure defaults are returned.
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 3f8ace9..715a09e 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -69,9 +69,11 @@ func TestExpandTilde(t *testing.T) {
 
 // TestLoad_defaults verifies all 10 default values when no config file exists.
 // HOME is redirected to a temp dir so Load() looks for a file that will not exist.
+// EDITOR is unset so EditCmd falls back to "vi".
 func TestLoad_defaults(t *testing.T) {
 	dir := t.TempDir()
 	t.Setenv("HOME", dir)
+	t.Setenv("EDITOR", "") // ensure fallback to "vi"
 
 	cfg := Load()
 
@@ -81,7 +83,7 @@ func TestLoad_defaults(t *testing.T) {
 		{"KeyFile", cfg.KeyFile, filepath.Join(dir, ".geheimlager.key")},
 		{"EncAlg", cfg.EncAlg, "AES-256-CBC"},
 		{"AddToIV", cfg.AddToIV, "Hello world"},
-		{"EditCmd", cfg.EditCmd, "hx"},
+		{"EditCmd", cfg.EditCmd, "vi"},
 		{"GnomeClipboardCmd", cfg.GnomeClipboardCmd, "gpaste-client"},
 		{"MacOSClipboardCmd", cfg.MacOSClipboardCmd, "pbcopy"},
 	}
@@ -98,6 +100,27 @@ func TestLoad_defaults(t *testing.T) {
 	}
 }
 
+// TestLoad_editorEnvVar verifies that when $EDITOR is set, defaultConfig uses it
+// as the EditCmd, and that a JSON config value overrides $EDITOR.
+func TestLoad_editorEnvVar(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("HOME", dir)
+
+	// $EDITOR set, no config file — EditCmd must equal $EDITOR.
+	t.Setenv("EDITOR", "nano")
+	cfg := Load()
+	if cfg.EditCmd != "nano" {
+		t.Errorf("EditCmd = %q; want nano (from $EDITOR)", cfg.EditCmd)
+	}
+
+	// JSON config overrides $EDITOR.
+	writeUserConfig(t, dir, `{"edit_cmd":"vim"}`)
+	cfg = Load()
+	if cfg.EditCmd != "vim" {
+		t.Errorf("EditCmd = %q; want vim (from config file)", cfg.EditCmd)
+	}
+}
+
 // TestLoad_override calls Load() directly (via a redirected HOME) and verifies
 // that JSON-supplied fields override defaults while absent fields keep defaults.
 func TestLoad_override(t *testing.T) {
@@ -143,10 +166,12 @@ func TestLoad_pathOverride(t *testing.T) {
 }
 
 // TestLoad_invalid_json verifies that invalid JSON causes Load() to emit a
-// warning to stderr and return defaults.
+// warning to stderr and return defaults (including EditCmd = "vi" when EDITOR
+// is unset).
 func TestLoad_invalid_json(t *testing.T) {
 	dir := t.TempDir()
 	t.Setenv("HOME", dir)
+	t.Setenv("EDITOR", "") // ensure fallback to "vi"
 	writeUserConfig(t, dir, `{invalid json}`)
 
 	var cfg Config
@@ -156,8 +181,8 @@ func TestLoad_invalid_json(t *testing.T) {
 		t.Errorf("expected warning on stderr, got: %q", stderr)
 	}
 	// Defaults must be returned with the redirected HOME.
-	if cfg.EditCmd != "hx" {
-		t.Errorf("EditCmd = %q; want hx (default)", cfg.EditCmd)
+	if cfg.EditCmd != "vi" {
+		t.Errorf("EditCmd = %q; want vi (default)", cfg.EditCmd)
 	}
 	if cfg.KeyLength != 32 {
 		t.Errorf("KeyLength = %d; want 32 (default)", cfg.KeyLength)
@@ -179,12 +204,14 @@ func TestLoad_missing_file_no_warning(t *testing.T) {
 
 // TestLoad_unreadable_file verifies that a config file that exists but cannot
 // be read emits a warning and returns defaults (the !os.IsNotExist branch).
+// EDITOR is unset so EditCmd falls back to "vi".
 func TestLoad_unreadable_file(t *testing.T) {
 	if os.Getuid() == 0 {
 		t.Skip("running as root: permission checks do not apply")
 	}
 	dir := t.TempDir()
 	t.Setenv("HOME", dir)
+	t.Setenv("EDITOR", "") // ensure fallback to "vi"
 	writeUserConfig(t, dir, `{"edit_cmd":"nvim"}`)
 
 	// Make the file unreadable.
@@ -201,7 +228,7 @@ func TestLoad_unreadable_file(t *testing.T) {
 		t.Errorf("expected warning on stderr, got: %q", stderr)
 	}
 	// Must return pure defaults, not the file content.
-	if cfg.EditCmd != "hx" {
-		t.Errorf("EditCmd = %q; want hx (default)", cfg.EditCmd)
+	if cfg.EditCmd != "vi" {
+		t.Errorf("EditCmd = %q; want vi (default)", cfg.EditCmd)
 	}
 }