Clarify model-generated and legacy app path types (#28577)

## Why

`ApiPathString` kind of implies that it can be used anywhere we pull a
path out of JSON, but it's not really appropriate for tool arguments
when the model might generate relative paths.

Prefer `String` for model-generated paths and we can handle the
conversion per feature for now and define a shared abstraction later if
it makes sense.

# What

Rename `ApiPathString` to `AppLegacyPathString` to clarify its role.

Expand the `path-types` skill to tell the model to leave tool args as
bare strings.

codex-rs/app-server-protocol/src/protocol/v2/permissions.rs

@@ -16,7 +16,7 @@ use codex_protocol::protocol::NetworkAccess as CoreNetworkAccess;
 use codex_protocol::request_permissions::PermissionGrantScope as CorePermissionGrantScope;
 use codex_protocol::request_permissions::RequestPermissionProfile as CoreRequestPermissionProfile;
 use codex_utils_absolute_path::AbsolutePathBuf;
-use codex_utils_path_uri::ApiPathString;
+use codex_utils_path_uri::LegacyAppPathString;
 use codex_utils_path_uri::PathConvention;
 use schemars::JsonSchema;
 use serde::Deserialize;
@@ -57,9 +57,9 @@ impl From<CoreNetworkApprovalContext> for NetworkApprovalContext {
 #[ts(export_to = "v2/")]
 pub struct AdditionalFileSystemPermissions {
     /// This will be removed in favor of `entries`.
-    pub read: Option<Vec<ApiPathString>>,
+    pub read: Option<Vec<LegacyAppPathString>>,
     /// This will be removed in favor of `entries`.
-    pub write: Option<Vec<ApiPathString>>,
+    pub write: Option<Vec<LegacyAppPathString>>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     #[ts(optional)]
     pub glob_scan_max_depth: Option<NonZeroUsize>,
@@ -78,7 +78,7 @@ impl From<CoreFileSystemPermissions<AbsolutePathBuf>> for AdditionalFileSystemPe
             if let Some(paths) = read.as_ref() {
                 entries.extend(paths.iter().map(|path| FileSystemSandboxEntry {
                     path: FileSystemPath::Path {
-                        path: ApiPathString::from_abs_path(path),
+                        path: LegacyAppPathString::from_abs_path(path),
                     },
                     access: FileSystemAccessMode::Read,
                 }));
@@ -86,14 +86,24 @@ impl From<CoreFileSystemPermissions<AbsolutePathBuf>> for AdditionalFileSystemPe
             if let Some(paths) = write.as_ref() {
                 entries.extend(paths.iter().map(|path| FileSystemSandboxEntry {
                     path: FileSystemPath::Path {
-                        path: ApiPathString::from_abs_path(path),
+                        path: LegacyAppPathString::from_abs_path(path),
                     },
                     access: FileSystemAccessMode::Write,
                 }));
             }
             Self {
-                read: read.map(|paths| paths.iter().map(ApiPathString::from_abs_path).collect()),
-                write: write.map(|paths| paths.iter().map(ApiPathString::from_abs_path).collect()),
+                read: read.map(|paths| {
+                    paths
+                        .iter()
+                        .map(LegacyAppPathString::from_abs_path)
+                        .collect()
+                }),
+                write: write.map(|paths| {
+                    paths
+                        .iter()
+                        .map(LegacyAppPathString::from_abs_path)
+                        .collect()
+                }),
                 glob_scan_max_depth: None,
                 entries: Some(entries),
             }
@@ -276,7 +286,7 @@ impl From<FileSystemSpecialPath> for CoreFileSystemSpecialPath {
 #[ts(export_to = "v2/")]
 // TODO(anp): Rename this type to distinguish it from the generic protocol FileSystemPath.
 pub enum FileSystemPath {
-    Path { path: ApiPathString },
+    Path { path: LegacyAppPathString },
     GlobPattern { pattern: String },
     Special { value: FileSystemSpecialPath },
 }
@@ -286,7 +296,7 @@ impl From<CoreFileSystemPath<AbsolutePathBuf>> for FileSystemPath {
     fn from(value: CoreFileSystemPath<AbsolutePathBuf>) -> Self {
         match value {
             CoreFileSystemPath::Path { path } => Self::Path {
-                path: ApiPathString::from_abs_path(&path),
+                path: LegacyAppPathString::from_abs_path(&path),
             },
             CoreFileSystemPath::GlobPattern { pattern } => Self::GlobPattern { pattern },
             CoreFileSystemPath::Special { value } => Self::Special {

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -35,7 +35,7 @@ use codex_protocol::user_input::UserInput as CoreUserInput;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_absolute_path::test_support::PathBufExt;
 use codex_utils_absolute_path::test_support::test_path_buf;
-use codex_utils_path_uri::ApiPathString;
+use codex_utils_path_uri::LegacyAppPathString;
 use pretty_assertions::assert_eq;
 use serde_json::Value as JsonValue;
 use serde_json::json;
@@ -579,8 +579,8 @@ fn additional_file_system_permissions_populates_entries_for_legacy_roots() {
     );
 
     let permissions = AdditionalFileSystemPermissions::from(core_permissions.clone());
-    let read_only_api_path = ApiPathString::from_abs_path(&read_only_path);
-    let read_write_api_path = ApiPathString::from_abs_path(&read_write_path);
+    let read_only_api_path = LegacyAppPathString::from_abs_path(&read_only_path);
+    let read_write_api_path = LegacyAppPathString::from_abs_path(&read_write_path);
 
     assert_eq!(
         permissions,