feat: pass helper executable paths via Arg0DispatchPaths (#12719)

## Why

`codex-rs/core/src/tools/runtimes/shell/unix_escalation.rs` previously
located `codex-execve-wrapper` by scanning `PATH` and sibling
directories. That lookup is brittle and can select the wrong binary when
the runtime environment differs from startup assumptions.

We already pass `codex-linux-sandbox` from `codex-arg0`;
`codex-execve-wrapper` should use the same startup-driven path plumbing.

## What changed

- Introduced `Arg0DispatchPaths` in `codex-arg0` to carry both helper
executable paths:
  - `codex_linux_sandbox_exe`
  - `main_execve_wrapper_exe`
- Updated `arg0_dispatch_or_else()` to pass `Arg0DispatchPaths` to
top-level binaries and preserve helper paths created in
`prepend_path_entry_for_codex_aliases()`.
- Threaded `Arg0DispatchPaths` through entrypoints in `cli`, `exec`,
`tui`, `app-server`, and `mcp-server`.
- Added `main_execve_wrapper_exe` to core configuration plumbing
(`Config`, `ConfigOverrides`, and `SessionServices`).
- Updated zsh-fork shell escalation to consume the configured
`main_execve_wrapper_exe` and removed path-sniffing fallback logic.
- Updated app-server config reload paths so reloaded configs keep the
same startup-provided helper executable paths.

## References

- [`Arg0DispatchPaths`
definition](e355b43d5c/codex-rs/arg0/src/lib.rs (L20-L24))
- [`arg0_dispatch_or_else()` forwarding both
paths](e355b43d5c/codex-rs/arg0/src/lib.rs (L145-L176))
- [zsh-fork escalation using configured wrapper
path](e355b43d5c/codex-rs/core/src/tools/runtimes/shell/unix_escalation.rs (L109-L150))

## Testing

- `cargo check -p codex-arg0 -p codex-core -p codex-exec -p codex-tui -p
codex-mcp-server -p codex-app-server`
- `cargo test -p codex-arg0`
- `cargo test -p codex-core tools::runtimes::shell::unix_escalation:: --
--nocapture`

codex-rs/exec/src/lib.rs

@@ -13,6 +13,7 @@ pub mod exec_events;
 pub use cli::Cli;
 pub use cli::Command;
 pub use cli::ReviewArgs;
+use codex_arg0::Arg0DispatchPaths;
 use codex_cloud_requirements::cloud_requirements_loader;
 use codex_core::AuthManager;
 use codex_core::LMSTUDIO_OSS_PROVIDER_ID;
@@ -90,7 +91,7 @@ struct ThreadEventEnvelope {
     suppress_output: bool,
 }
 
-pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> anyhow::Result<()> {
+pub async fn run_main(cli: Cli, arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
     if let Err(err) = set_default_originator("codex_exec".to_string()) {
         tracing::warn!(?err, "Failed to set codex exec originator override {err:?}");
     }
@@ -271,7 +272,8 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         sandbox_mode,
         cwd: resolved_cwd,
         model_provider: model_provider.clone(),
-        codex_linux_sandbox_exe,
+        codex_linux_sandbox_exe: arg0_paths.codex_linux_sandbox_exe.clone(),
+        main_execve_wrapper_exe: arg0_paths.main_execve_wrapper_exe.clone(),
         js_repl_node_path: None,
         js_repl_node_module_dirs: None,
         zsh_path: None,