feat: add SAF directory picker for workspace fields (Step 5)

Add "directory" schema type for workspace/data_dir fields in the gateway
and render a SAF OpenDocumentTree picker in the Android Config UI.

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

android/backend/config/src/main/java/io/clawdroid/backend/config/ConfigSectionDetailScreen.kt

@@ -1,5 +1,10 @@
 package io.clawdroid.backend.config
 
+import android.content.Intent
+import android.net.Uri
+import android.provider.DocumentsContract
+import androidx.activity.compose.rememberLauncherForActivityResult
+import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -37,8 +42,10 @@ import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.input.KeyboardType
@@ -51,6 +58,7 @@ import io.clawdroid.core.ui.theme.GlassWhite
 import io.clawdroid.core.ui.theme.NeonCyan
 import io.clawdroid.core.ui.theme.TextPrimary
 import io.clawdroid.core.ui.theme.TextSecondary
+import kotlinx.coroutines.launch
 import org.koin.androidx.compose.koinViewModel
 
 @OptIn(ExperimentalMaterial3Api::class)
@@ -147,6 +155,7 @@ fun ConfigSectionDetailScreen(
                         ConfigField(
                             field = field,
                             onValueChanged = { viewModel.onFieldValueChanged(field.key, it) },
+                            snackbarHostState = snackbarHostState,
                         )
                     }
                 }
@@ -168,12 +177,14 @@ fun ConfigSectionDetailScreen(
 private fun ConfigField(
     field: FieldState,
     onValueChanged: (String) -> Unit,
+    snackbarHostState: SnackbarHostState? = null,
 ) {
     when (field.type) {
         "bool" -> BoolField(field, onValueChanged)
         "int" -> NumberField(field, onValueChanged, KeyboardType.Number)
         "float" -> NumberField(field, onValueChanged, KeyboardType.Decimal)
         "[]string" -> StringArrayField(field, onValueChanged)
+        "directory" -> DirectoryField(field, onValueChanged, snackbarHostState)
         "map", "[]any" -> ReadOnlyField(field)
         else -> StringField(field, onValueChanged)
     }
@@ -281,6 +292,81 @@ private fun ReadOnlyField(field: FieldState) {
     )
 }
 
+@Composable
+private fun DirectoryField(
+    field: FieldState,
+    onValueChanged: (String) -> Unit,
+    snackbarHostState: SnackbarHostState?,
+) {
+    val context = LocalContext.current
+    val scope = rememberCoroutineScope()
+
+    val launcher = rememberLauncherForActivityResult(
+        contract = ActivityResultContracts.OpenDocumentTree()
+    ) { uri: Uri? ->
+        if (uri == null) return@rememberLauncherForActivityResult
+        context.contentResolver.takePersistableUriPermission(
+            uri,
+            Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION,
+        )
+        val path = safUriToPath(uri)
+        if (path != null) {
+            onValueChanged(path)
+        } else {
+            scope.launch {
+                snackbarHostState?.showSnackbar("Internal storage only")
+            }
+        }
+    }
+
+    Column {
+        OutlinedTextField(
+            value = field.value,
+            onValueChange = onValueChanged,
+            label = { Text(field.label, color = TextSecondary) },
+            singleLine = true,
+            trailingIcon = {
+                IconButton(onClick = { launcher.launch(null) }) {
+                    Icon(
+                        painter = painterResource(LucideR.drawable.lucide_ic_folder_open),
+                        contentDescription = "Browse",
+                        tint = NeonCyan,
+                    )
+                }
+            },
+            colors = configFieldColors(),
+            modifier = Modifier.fillMaxWidth(),
+        )
+        Text(
+            "Internal storage only for SAF picker",
+            style = MaterialTheme.typography.labelSmall,
+            color = TextSecondary.copy(alpha = 0.6f),
+            modifier = Modifier.padding(start = 16.dp, top = 2.dp),
+        )
+    }
+}
+
+/**
+ * Converts a SAF tree URI to a filesystem path.
+ * Only internal storage (`primary:...`) is supported.
+ */
+private fun safUriToPath(uri: Uri): String? {
+    val docId = try {
+        DocumentsContract.getTreeDocumentId(uri)
+    } catch (_: Exception) {
+        return null
+    }
+
+    if (!docId.startsWith("primary:")) return null
+
+    val relativePath = docId.removePrefix("primary:")
+    return if (relativePath.isEmpty()) {
+        "/storage/emulated/0"
+    } else {
+        "/storage/emulated/0/$relativePath"
+    }
+}
+
 @Composable
 private fun configFieldColors() = OutlinedTextFieldDefaults.colors(
     focusedBorderColor = NeonCyan.copy(alpha = 0.5f),

pkg/gateway/schema.go

@@ -44,6 +44,14 @@ var secretKeys = map[string]bool{
 	"channel_access_token": true,
 }
 
+// directoryKeys lists full dot-separated JSON keys that represent directory paths.
+// Fields matching these keys are reported as type "directory" so that
+// Android can render a SAF directory-picker instead of a plain text field.
+var directoryKeys = map[string]bool{
+	"defaults.workspace": true,
+	"defaults.data_dir":  true,
+}
+
 // BuildSchema generates a SchemaResponse by reflecting over a default Config.
 func BuildSchema(defaultCfg *config.Config) SchemaResponse {
 	var sections []SchemaSection
@@ -130,6 +138,11 @@ func buildFields(t reflect.Type, v reflect.Value, prefix string) []SchemaField {
 			defVal = fieldVal.Interface()
 		}
 
+		// Override type for directory-path fields
+		if schemaType == "string" && directoryKeys[fullKey] {
+			schemaType = "directory"
+		}
+
 		fields = append(fields, SchemaField{
 			Key:     fullKey,
 			Label:   snakeToTitle(jk),

pkg/gateway/server_test.go

@@ -2470,6 +2470,41 @@ func TestBuildSchema_AgentsSectionFields(t *testing.T) {
 	}
 }
 
+// --- #28b: directory type override ---
+
+func TestBuildSchema_DirectoryType(t *testing.T) {
+	schema := BuildSchema(config.DefaultConfig())
+
+	// Find the agents section which contains the defaults sub-fields
+	var agentsFields []SchemaField
+	for _, sec := range schema.Sections {
+		if sec.Key == "agents" {
+			agentsFields = sec.Fields
+			break
+		}
+	}
+	if agentsFields == nil {
+		t.Fatal("agents section not found in schema")
+	}
+
+	fieldByKey := make(map[string]SchemaField)
+	for _, f := range agentsFields {
+		fieldByKey[f.Key] = f
+	}
+
+	dirFields := []string{"defaults.workspace", "defaults.data_dir"}
+	for _, k := range dirFields {
+		f, ok := fieldByKey[k]
+		if !ok {
+			t.Errorf("field %q not found in agents section", k)
+			continue
+		}
+		if f.Type != "directory" {
+			t.Errorf("field %q: want type %q, got %q", k, "directory", f.Type)
+		}
+	}
+}
+
 // --- #29: rate_limits section fields in schema ---
 
 func TestBuildSchema_RateLimitsSectionFields(t *testing.T) {