chore: use @plugin instead of $plugin for plaintext mentions (#13921)

change plaintext plugin-mentions from `$plugin` to `@plugin`, ensure TUI
can correctly decode these from history.

tested locally, added/updated tests.

codex-rs/core/src/lib.rs

@@ -55,6 +55,7 @@ pub use mcp_connection_manager::SandboxState;
 pub use text_encoding::bytes_to_string_smart;
 mod mcp_tool_call;
 mod memories;
+pub mod mention_syntax;
 mod mentions;
 mod message_history;
 mod model_provider_info;

codex-rs/core/src/mention_syntax.rs

@@ -0,0 +1,4 @@
+// Default plaintext sigil for tools.
+pub const TOOL_MENTION_SIGIL: char = '$';
+// Plugins use `@` in linked plaintext outside TUI.
+pub const PLUGIN_TEXT_MENTION_SIGIL: char = '@';

codex-rs/core/src/mentions.rs

@@ -5,11 +5,13 @@ use std::path::PathBuf;
 use codex_protocol::user_input::UserInput;
 
 use crate::connectors;
+use crate::mention_syntax::PLUGIN_TEXT_MENTION_SIGIL;
+use crate::mention_syntax::TOOL_MENTION_SIGIL;
 use crate::plugins::PluginCapabilitySummary;
 use crate::skills::SkillMetadata;
 use crate::skills::injection::ToolMentionKind;
 use crate::skills::injection::app_id_from_path;
-use crate::skills::injection::extract_tool_mentions;
+use crate::skills::injection::extract_tool_mentions_with_sigil;
 use crate::skills::injection::plugin_config_name_from_path;
 use crate::skills::injection::tool_kind_for_path;
 
@@ -19,10 +21,17 @@ pub(crate) struct CollectedToolMentions {
 }
 
 pub(crate) fn collect_tool_mentions_from_messages(messages: &[String]) -> CollectedToolMentions {
+    collect_tool_mentions_from_messages_with_sigil(messages, TOOL_MENTION_SIGIL)
+}
+
+fn collect_tool_mentions_from_messages_with_sigil(
+    messages: &[String],
+    sigil: char,
+) -> CollectedToolMentions {
     let mut plain_names = HashSet::new();
     let mut paths = HashSet::new();
     for message in messages {
-        let mentions = extract_tool_mentions(message);
+        let mentions = extract_tool_mentions_with_sigil(message, sigil);
         plain_names.extend(mentions.plain_names().map(str::to_string));
         paths.extend(mentions.paths().map(str::to_string));
     }
@@ -50,7 +59,7 @@ pub(crate) fn collect_explicit_app_ids(input: &[UserInput]) -> HashSet<String> {
         .collect()
 }
 
-/// Collect explicit structured `plugin://...` mentions.
+/// Collect explicit structured or linked `plugin://...` mentions.
 pub(crate) fn collect_explicit_plugin_mentions(
     input: &[UserInput],
     plugins: &[PluginCapabilitySummary],
@@ -73,7 +82,11 @@ pub(crate) fn collect_explicit_plugin_mentions(
             UserInput::Mention { path, .. } => Some(path.clone()),
             _ => None,
         })
-        .chain(collect_tool_mentions_from_messages(&messages).paths)
+        .chain(
+            // Plugin plaintext links use `@`, not the default `$` tool sigil.
+            collect_tool_mentions_from_messages_with_sigil(&messages, PLUGIN_TEXT_MENTION_SIGIL)
+                .paths,
+        )
         .filter(|path| tool_kind_for_path(path.as_str()) == ToolMentionKind::Plugin)
         .filter_map(|path| plugin_config_name_from_path(path.as_str()).map(str::to_string))
         .collect();
@@ -222,7 +235,7 @@ mod tests {
         ];
 
         let mentioned = collect_explicit_plugin_mentions(
-            &[text_input("use [$sample](plugin://sample@test)")],
+            &[text_input("use [@sample](plugin://sample@test)")],
             &plugins,
         );
 
@@ -238,7 +251,7 @@ mod tests {
 
         let mentioned = collect_explicit_plugin_mentions(
             &[
-                text_input("use [$sample](plugin://sample@test)"),
+                text_input("use [@sample](plugin://sample@test)"),
                 UserInput::Mention {
                     name: "sample".to_string(),
                     path: "plugin://sample@test".to_string(),
@@ -263,4 +276,16 @@ mod tests {
 
         assert_eq!(mentioned, Vec::<PluginCapabilitySummary>::new());
     }
+
+    #[test]
+    fn collect_explicit_plugin_mentions_ignores_dollar_linked_plugin_mentions() {
+        let plugins = vec![plugin("sample@test", "sample")];
+
+        let mentioned = collect_explicit_plugin_mentions(
+            &[text_input("use [$sample](plugin://sample@test)")],
+            &plugins,
+        );
+
+        assert_eq!(mentioned, Vec::<PluginCapabilitySummary>::new());
+    }
 }

codex-rs/core/src/skills/injection.rs

@@ -7,6 +7,7 @@ use crate::analytics_client::InvocationType;
 use crate::analytics_client::SkillInvocation;
 use crate::analytics_client::TrackEventsContext;
 use crate::instructions::SkillInstructions;
+use crate::mention_syntax::TOOL_MENTION_SIGIL;
 use crate::mentions::build_skill_name_counts;
 use crate::skills::SkillMetadata;
 use codex_otel::SessionTelemetry;
@@ -232,10 +233,10 @@ pub(crate) fn normalize_skill_path(path: &str) -> &str {
 /// resource path is present, it is captured for exact path matching while also tracking
 /// the name for fallback matching.
 pub(crate) fn extract_tool_mentions(text: &str) -> ToolMentions<'_> {
-    extract_tool_mentions_with_sigil(text, '$')
+    extract_tool_mentions_with_sigil(text, TOOL_MENTION_SIGIL)
 }
 
-fn extract_tool_mentions_with_sigil(text: &str, sigil: char) -> ToolMentions<'_> {
+pub(crate) fn extract_tool_mentions_with_sigil(text: &str, sigil: char) -> ToolMentions<'_> {
     let text_bytes = text.as_bytes();
     let mut mentioned_names: HashSet<&str> = HashSet::new();
     let mut mentioned_paths: HashSet<&str> = HashSet::new();