Add FS abstraction and use in view_image (#14960)

Adds an environment crate and environment + file system abstraction.

Environment is a combination of attributes and services specific to
environment the agent is connected to:
File system, process management, OS, default shell.

The goal is to move most of agent logic that assumes environment to work
through the environment abstraction.

codex-rs/core/src/codex.rs

@@ -60,6 +60,7 @@ use chrono::Local;
 use chrono::Utc;
 use codex_app_server_protocol::McpServerElicitationRequest;
 use codex_app_server_protocol::McpServerElicitationRequestParams;
+use codex_environment::Environment;
 use codex_hooks::HookEvent;
 use codex_hooks::HookEventAfterAgent;
 use codex_hooks::HookPayload;
@@ -785,6 +786,7 @@ pub(crate) struct TurnContext {
     pub(crate) reasoning_effort: Option<ReasoningEffortConfig>,
     pub(crate) reasoning_summary: ReasoningSummaryConfig,
     pub(crate) session_source: SessionSource,
+    pub(crate) environment: Arc<Environment>,
     /// The session's current working directory. All relative paths provided by
     /// the model as well as sandbox policies are resolved against this path
     /// instead of `std::env::current_dir()`.
@@ -894,6 +896,7 @@ impl TurnContext {
             reasoning_effort,
             reasoning_summary: self.reasoning_summary,
             session_source: self.session_source.clone(),
+            environment: Arc::clone(&self.environment),
             cwd: self.cwd.clone(),
             current_date: self.current_date.clone(),
             timezone: self.timezone.clone(),
@@ -1282,6 +1285,7 @@ impl Session {
         model_info: ModelInfo,
         models_manager: &ModelsManager,
         network: Option<NetworkProxy>,
+        environment: Arc<Environment>,
         sub_id: String,
         js_repl: Arc<JsReplHandle>,
         skills_outcome: Arc<SkillLoadOutcome>,
@@ -1338,6 +1342,7 @@ impl Session {
             reasoning_effort,
             reasoning_summary,
             session_source,
+            environment,
             cwd,
             current_date: Some(current_date),
             timezone: Some(timezone),
@@ -1810,6 +1815,7 @@ impl Session {
             code_mode_service: crate::tools::code_mode::CodeModeService::new(
                 config.js_repl_node_path.clone(),
             ),
+            environment: Arc::new(Environment),
         };
         let js_repl = Arc::new(JsReplHandle::with_node_path(
             config.js_repl_node_path.clone(),
@@ -2389,6 +2395,7 @@ impl Session {
                 .network_proxy
                 .as_ref()
                 .map(StartedNetworkProxy::proxy),
+            Arc::clone(&self.services.environment),
             sub_id,
             Arc::clone(&self.js_repl),
             skills_outcome,
@@ -5198,6 +5205,7 @@ async fn spawn_review_thread(
         reasoning_effort,
         reasoning_summary,
         session_source,
+        environment: Arc::clone(&parent_turn_context.environment),
         tools_config,
         features: parent_turn_context.features.clone(),
         ghost_snapshot: parent_turn_context.ghost_snapshot.clone(),