Better handling skill depdenencies on ENV VAR. (#9017)

An experimental flow for env var skill dependencies. Skills can now
declare required env vars in SKILL.md; if missing, the CLI prompts the
user to get the value, and Core will store it in memory (eventually to a
local persistent store)
<img width="790" height="169" alt="image"
src="https://github.com/user-attachments/assets/cd928918-9403-43cb-a7e7-b8d59bcccd9a"
/>

codex-rs/core/src/codex.rs

@@ -168,10 +168,12 @@ use crate::skills::SkillInjections;
 use crate::skills::SkillMetadata;
 use crate::skills::SkillsManager;
 use crate::skills::build_skill_injections;
+use crate::skills::collect_env_var_dependencies;
 use crate::skills::collect_explicit_skill_mentions;
 use crate::skills::injection::ToolMentionKind;
 use crate::skills::injection::app_id_from_path;
 use crate::skills::injection::tool_kind_for_path;
+use crate::skills::resolve_skill_dependencies_for_turn;
 use crate::state::ActiveTurn;
 use crate::state::SessionServices;
 use crate::state::SessionState;
@@ -1953,6 +1955,16 @@ impl Session {
         state.record_mcp_dependency_prompted(names);
     }
 
+    pub async fn dependency_env(&self) -> HashMap<String, String> {
+        let state = self.state.lock().await;
+        state.dependency_env()
+    }
+
+    pub async fn set_dependency_env(&self, values: HashMap<String, String>) {
+        let mut state = self.state.lock().await;
+        state.set_dependency_env(values);
+    }
+
     pub(crate) async fn set_server_reasoning_included(&self, included: bool) {
         let mut state = self.state.lock().await;
         state.set_server_reasoning_included(included);
@@ -3218,6 +3230,15 @@ pub(crate) async fn run_turn(
     });
     let explicit_app_paths = collect_explicit_app_paths(&input);
 
+    let config = turn_context.client.config();
+    if config
+        .features
+        .enabled(Feature::SkillEnvVarDependencyPrompt)
+    {
+        let env_var_dependencies = collect_env_var_dependencies(&mentioned_skills);
+        resolve_skill_dependencies_for_turn(&sess, &turn_context, &env_var_dependencies).await;
+    }
+
     maybe_prompt_and_install_mcp_dependencies(
         sess.as_ref(),
         turn_context.as_ref(),