fix code mode host packaging compatibility

codex-rs/code-mode/src/remote_session.rs

@@ -1,3 +1,4 @@
+use std::io;
 use std::path::PathBuf;
 use std::sync::Arc;
 use std::sync::Mutex as StdMutex;
@@ -63,7 +64,7 @@ impl ProcessOwnedCodeModeSessionProvider {
 
 impl Default for ProcessOwnedCodeModeSessionProvider {
     fn default() -> Self {
-        Self::with_host_program(InstallContext::current().code_mode_host_program())
+        Self::with_host_program(default_host_program())
     }
 }
 
@@ -192,9 +193,7 @@ impl ProcessOwnedCodeModeSession {
     pub fn new() -> Self {
         Self::with_process_host(
             Arc::new(NoopCodeModeSessionDelegate),
-            Arc::new(OwnedProcessHost::new(
-                InstallContext::current().code_mode_host_program(),
-            )),
+            Arc::new(OwnedProcessHost::new(default_host_program())),
         )
     }
 
@@ -493,6 +492,26 @@ impl CodeModeSession for ProcessOwnedCodeModeSession {
     }
 }
 
+fn default_host_program() -> PathBuf {
+    InstallContext::current()
+        .code_mode_host_program()
+        .unwrap_or_else(|| resolve_host_program(std::env::current_exe()))
+}
+
+fn resolve_host_program(current_exe: io::Result<PathBuf>) -> PathBuf {
+    let executable_name = if cfg!(windows) {
+        "codex-code-mode-host.exe"
+    } else {
+        "codex-code-mode-host"
+    };
+    if let Ok(current_exe) = current_exe
+        && let Some(parent) = current_exe.parent()
+    {
+        return parent.join(executable_name);
+    }
+    PathBuf::from(executable_name)
+}
+
 #[cfg(test)]
 #[path = "remote_session_tests.rs"]
 mod tests;

codex-rs/code-mode/src/remote_session_tests.rs

@@ -1,3 +1,5 @@
+use std::io;
+use std::path::PathBuf;
 use std::sync::Arc;
 
 use codex_code_mode_protocol::CodeModeSessionProvider;
@@ -8,6 +10,7 @@ use pretty_assertions::assert_eq;
 
 use super::ProcessOwnedCodeModeSession;
 use super::ProcessOwnedCodeModeSessionProvider;
+use super::resolve_host_program;
 use crate::NoopCodeModeSessionDelegate;
 
 #[test]
@@ -20,6 +23,37 @@ fn provider_reuses_its_live_process_host() {
     assert!(Arc::ptr_eq(&first, &second));
 }
 
+#[test]
+fn host_program_is_next_to_the_main_executable_even_when_missing() {
+    let executable_name = if cfg!(windows) {
+        "codex-code-mode-host.exe"
+    } else {
+        "codex-code-mode-host"
+    };
+
+    assert_eq!(
+        resolve_host_program(Ok(PathBuf::from("/opt/codex/bin/codex"))),
+        PathBuf::from("/opt/codex/bin").join(executable_name)
+    );
+}
+
+#[test]
+fn host_program_falls_back_to_its_name_when_main_executable_is_unknown() {
+    let executable_name = if cfg!(windows) {
+        "codex-code-mode-host.exe"
+    } else {
+        "codex-code-mode-host"
+    };
+
+    assert_eq!(
+        resolve_host_program(Err(io::Error::new(
+            io::ErrorKind::NotFound,
+            "missing executable"
+        ))),
+        PathBuf::from(executable_name)
+    );
+}
+
 #[tokio::test]
 async fn provider_falls_back_to_in_process_session_when_host_is_missing() {
     let provider = ProcessOwnedCodeModeSessionProvider::with_host_program(