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/v2.rs

@@ -30,6 +30,8 @@ use codex_protocol::protocol::SkillMetadata as CoreSkillMetadata;
 use codex_protocol::protocol::SkillScope as CoreSkillScope;
 use codex_protocol::protocol::TokenUsage as CoreTokenUsage;
 use codex_protocol::protocol::TokenUsageInfo as CoreTokenUsageInfo;
+use codex_protocol::user_input::ByteRange as CoreByteRange;
+use codex_protocol::user_input::TextElement as CoreTextElement;
 use codex_protocol::user_input::UserInput as CoreUserInput;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use mcp_types::ContentBlock as McpContentBlock;
@@ -1589,6 +1591,24 @@ pub struct ByteRange {
     pub end: usize,
 }
 
+impl From<CoreByteRange> for ByteRange {
+    fn from(value: CoreByteRange) -> Self {
+        Self {
+            start: value.start,
+            end: value.end,
+        }
+    }
+}
+
+impl From<ByteRange> for CoreByteRange {
+    fn from(value: ByteRange) -> Self {
+        Self {
+            start: value.start,
+            end: value.end,
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
@@ -1599,6 +1619,24 @@ pub struct TextElement {
     pub placeholder: Option<String>,
 }
 
+impl From<CoreTextElement> for TextElement {
+    fn from(value: CoreTextElement) -> Self {
+        Self {
+            byte_range: value.byte_range.into(),
+            placeholder: value.placeholder,
+        }
+    }
+}
+
+impl From<TextElement> for CoreTextElement {
+    fn from(value: TextElement) -> Self {
+        Self {
+            byte_range: value.byte_range.into(),
+            placeholder: value.placeholder,
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(tag = "type", rename_all = "camelCase")]
 #[ts(tag = "type")]
@@ -1625,10 +1663,12 @@ pub enum UserInput {
 impl UserInput {
     pub fn into_core(self) -> CoreUserInput {
         match self {
-            UserInput::Text { text, .. } => CoreUserInput::Text {
+            UserInput::Text {
                 text,
-                // TODO: Thread text element ranges into v2 inputs. Empty keeps old behavior.
-                text_elements: Vec::new(),
+                text_elements,
+            } => CoreUserInput::Text {
+                text,
+                text_elements: text_elements.into_iter().map(Into::into).collect(),
             },
             UserInput::Image { url } => CoreUserInput::Image { image_url: url },
             UserInput::LocalImage { path } => CoreUserInput::LocalImage { path },
@@ -1640,10 +1680,12 @@ impl UserInput {
 impl From<CoreUserInput> for UserInput {
     fn from(value: CoreUserInput) -> Self {
         match value {
-            CoreUserInput::Text { text, .. } => UserInput::Text {
+            CoreUserInput::Text {
                 text,
-                // TODO: Thread text element ranges from core into v2 inputs.
-                text_elements: Vec::new(),
+                text_elements,
+            } => UserInput::Text {
+                text,
+                text_elements: text_elements.into_iter().map(Into::into).collect(),
             },
             CoreUserInput::Image { image_url } => UserInput::Image { url: image_url },
             CoreUserInput::LocalImage { path } => UserInput::LocalImage { path },