Add text element metadata to protocol, app server, and core (#9331)

The second part of breaking up PR
https://github.com/openai/codex/pull/9116

Summary:

- Add `TextElement` / `ByteRange` to protocol user inputs and user
message events with defaults.
- Thread `text_elements` through app-server v1/v2 request handling and
history rebuild.
- Preserve UI metadata only in user input/events (not `ContentItem`)
while keeping local image attachments in user events for rehydration.

Details:

- Protocol: `UserInput::Text` carries `text_elements`;
`UserMessageEvent` carries `text_elements` + `local_images`.
Serialization includes empty vectors for backward compatibility.
- app-server-protocol: v1 defines `V1TextElement` / `V1ByteRange` in
camelCase with conversions; v2 uses its own camelCase wrapper.
- app-server: v1/v2 input mapping includes `text_elements`; thread
history rebuilds include them.
- Core: user event emission preserves UI metadata while model history
stays clean; history replay round-trips the metadata.

codex-rs/app-server-protocol/src/protocol/v1.rs

@@ -16,6 +16,8 @@ use codex_protocol::protocol::ReviewDecision;
 use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::TurnAbortReason;
+use codex_protocol::user_input::ByteRange as CoreByteRange;
+use codex_protocol::user_input::TextElement as CoreTextElement;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use schemars::JsonSchema;
 use serde::Deserialize;
@@ -444,9 +446,74 @@ pub struct RemoveConversationListenerParams {
 #[serde(rename_all = "camelCase")]
 #[serde(tag = "type", content = "data")]
 pub enum InputItem {
-    Text { text: String },
-    Image { image_url: String },
-    LocalImage { path: PathBuf },
+    Text {
+        text: String,
+        /// UI-defined spans within `text` used to render or persist special elements.
+        #[serde(default)]
+        text_elements: Vec<V1TextElement>,
+    },
+    Image {
+        image_url: String,
+    },
+    LocalImage {
+        path: PathBuf,
+    },
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(rename = "ByteRange")]
+pub struct V1ByteRange {
+    /// Start byte offset (inclusive) within the UTF-8 text buffer.
+    pub start: usize,
+    /// End byte offset (exclusive) within the UTF-8 text buffer.
+    pub end: usize,
+}
+
+impl From<CoreByteRange> for V1ByteRange {
+    fn from(value: CoreByteRange) -> Self {
+        Self {
+            start: value.start,
+            end: value.end,
+        }
+    }
+}
+
+impl From<V1ByteRange> for CoreByteRange {
+    fn from(value: V1ByteRange) -> Self {
+        Self {
+            start: value.start,
+            end: value.end,
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(rename = "TextElement")]
+pub struct V1TextElement {
+    /// Byte range in the parent `text` buffer that this element occupies.
+    pub byte_range: V1ByteRange,
+    /// Optional human-readable placeholder for the element, displayed in the UI.
+    pub placeholder: Option<String>,
+}
+
+impl From<CoreTextElement> for V1TextElement {
+    fn from(value: CoreTextElement) -> Self {
+        Self {
+            byte_range: value.byte_range.into(),
+            placeholder: value.placeholder,
+        }
+    }
+}
+
+impl From<V1TextElement> for CoreTextElement {
+    fn from(value: V1TextElement) -> Self {
+        Self {
+            byte_range: value.byte_range.into(),
+            placeholder: value.placeholder,
+        }
+    }
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]