[codex] simplify memory read metrics (#28164)

## Why

Memory read telemetry currently reconstructs the executable shell
command after a tool call finishes. That duplicates shell, login-policy,
and cwd resolution owned by the tool handlers, and can diverge from the
environment-specific command that unified exec actually ran.

## What changed

- Expose the existing restricted shell-script parser directly for raw
script text.
- Parse `shell_command` and `exec_command` input into plain command argv
before classifying memory reads.
- Preserve all-or-nothing safe-command validation for multi-command
scripts.
- Remove cwd resolution, shell selection, and the unnecessary async
boundary from memory read metric emission.

## Testing

- `just test -p codex-shell-command`
- `cargo check -p codex-core`

codex-rs/core/src/memory_usage.rs

@@ -5,20 +5,15 @@ use crate::tools::handlers::unified_exec::ExecCommandArgs;
 use codex_memories_read::usage::MEMORIES_USAGE_METRIC;
 use codex_memories_read::usage::memories_usage_kinds_from_command;
 use codex_protocol::models::ShellCommandToolCallParams;
-use std::path::PathBuf;
 
-pub(crate) async fn emit_metric_for_tool_read(invocation: &ToolInvocation, success: bool) {
-    let Some((command, _)) = shell_command_for_invocation(invocation) else {
+pub(crate) fn emit_metric_for_tool_read(invocation: &ToolInvocation, success: bool) {
+    let Some(command) = shell_script_for_invocation(invocation) else {
         return;
     };
-    let kinds = memories_usage_kinds_from_command(&command);
-    if kinds.is_empty() {
-        return;
-    }
 
     let success = if success { "true" } else { "false" };
     let tool_name = flat_tool_name(&invocation.tool_name);
-    for kind in kinds {
+    for kind in memories_usage_kinds_from_command(&command) {
         invocation.turn.session_telemetry.counter(
             MEMORIES_USAGE_METRIC,
             /*inc*/ 1,
@@ -31,7 +26,7 @@ pub(crate) async fn emit_metric_for_tool_read(invocation: &ToolInvocation, succe
     }
 }
 
-fn shell_command_for_invocation(invocation: &ToolInvocation) -> Option<(Vec<String>, PathBuf)> {
+fn shell_script_for_invocation(invocation: &ToolInvocation) -> Option<String> {
     let ToolPayload::Function { arguments } = &invocation.payload else {
         return None;
     };
@@ -42,39 +37,10 @@ fn shell_command_for_invocation(invocation: &ToolInvocation) -> Option<(Vec<Stri
     ) {
         (None, "shell_command") => serde_json::from_str::<ShellCommandToolCallParams>(arguments)
             .ok()
-            .map(|params| {
-                if !invocation.turn.config.permissions.allow_login_shell
-                    && params.login == Some(true)
-                {
-                    #[allow(deprecated)]
-                    let cwd = invocation.turn.resolve_path(params.workdir).to_path_buf();
-                    return (Vec::new(), cwd);
-                }
-                let use_login_shell = params
-                    .login
-                    .unwrap_or(invocation.turn.config.permissions.allow_login_shell);
-                let command = invocation
-                    .session
-                    .user_shell()
-                    .derive_exec_args(&params.command, use_login_shell);
-                #[allow(deprecated)]
-                let cwd = invocation.turn.resolve_path(params.workdir).to_path_buf();
-                (command, cwd)
-            }),
+            .map(|params| params.command),
         (None, "exec_command") => serde_json::from_str::<ExecCommandArgs>(arguments)
             .ok()
-            .and_then(|params| {
-                let command = crate::tools::handlers::unified_exec::get_command(
-                    &params,
-                    invocation.session.user_shell(),
-                    &invocation.turn.unified_exec_shell_mode,
-                    invocation.turn.config.permissions.allow_login_shell,
-                )
-                .ok()?;
-                #[allow(deprecated)]
-                let cwd = invocation.turn.resolve_path(params.workdir).to_path_buf();
-                Some((command.command, cwd))
-            }),
+            .map(|params| params.cmd),
         (Some(_), _) | (None, _) => None,
     }
 }