fix(toolinstall): soft-fail auto-detect installs

pkg/toolinstall/resolver.go

@@ -25,14 +25,23 @@ func EnsureCommand(ctx context.Context, command, version string) (string, error)
 		return command, nil
 	}
 
-	lower := strings.ToLower(strings.TrimSpace(version))
+	version = strings.TrimSpace(version)
+	lower := strings.ToLower(version)
 	if lower == "false" || lower == "off" {
 		return command, nil
 	}
 
 	resolvedPath, err := resolve(ctx, command, version)
 	if err != nil {
-		return "", fmt.Errorf("auto-installing command %q: %w", command, err)
+		if version != "" {
+			return "", fmt.Errorf("auto-installing command %q: %w", command, err)
+		}
+
+		slog.Warn("Auto-install failed, falling back to original command",
+			"command", command,
+			"error", err,
+		)
+		return command, nil
 	}
 
 	return resolvedPath, nil

pkg/toolinstall/resolver_test.go

@@ -50,7 +50,16 @@ func TestEnsureCommand_DisabledPerToolset(t *testing.T) {
 	}
 }
 
-func TestEnsureCommand_SoftFail(t *testing.T) {
+func TestEnsureCommand_AutoDetectFailureFallsBackToOriginalCommand(t *testing.T) {
+	t.Setenv("DOCKER_AGENT_TOOLS_DIR", t.TempDir())
+	t.Setenv("DOCKER_AGENT_AUTO_INSTALL", "")
+
+	result, err := EnsureCommand(t.Context(), "nonexistent-tool", "")
+	require.NoError(t, err)
+	assert.Equal(t, "nonexistent-tool", result)
+}
+
+func TestEnsureCommand_ExplicitVersionFailureStillErrors(t *testing.T) {
 	t.Setenv("DOCKER_AGENT_TOOLS_DIR", t.TempDir())
 	t.Setenv("DOCKER_AGENT_AUTO_INSTALL", "")
 
@@ -73,7 +82,7 @@ func TestEnsureCommand_FoundInBinDir(t *testing.T) {
 	assert.Equal(t, fakeBin, result)
 }
 
-func TestEnsureCommand_NonExecutableInBinDirIsSkipped(t *testing.T) {
+func TestEnsureCommand_NonExecutableInBinDirFallsBackToOriginalCommand(t *testing.T) {
 	toolsDir := t.TempDir()
 	t.Setenv("DOCKER_AGENT_TOOLS_DIR", toolsDir)
 	t.Setenv("DOCKER_AGENT_AUTO_INSTALL", "")
@@ -82,9 +91,9 @@ func TestEnsureCommand_NonExecutableInBinDirIsSkipped(t *testing.T) {
 	require.NoError(t, os.MkdirAll(binDir, 0o755))
 	require.NoError(t, os.WriteFile(filepath.Join(binDir, "not-executable"), []byte("data"), 0o644))
 
-	// Falls through to auto-install → fails → returns error.
-	_, err := EnsureCommand(t.Context(), "not-executable", "")
-	require.Error(t, err)
+	result, err := EnsureCommand(t.Context(), "not-executable", "")
+	require.NoError(t, err)
+	assert.Equal(t, "not-executable", result)
 }
 
 // --- resolve tests ---