Fix plugin cache panic when cwd is unavailable (#18499)

## Summary

Fixes #16637. (I hit this bug after 11h of work on a long-running task.)

Plugin cache initialization could panic when an already-absolute cache
path was normalized through `AbsolutePathBuf::from_absolute_path`,
because that path still consulted `current_dir()`.

This changes absolute-path normalization so already-absolute paths do
not depend on cwd, and makes plugin cache root construction available as
a fallible path through `PluginStore::try_new()`. Plugin cache subpaths
now use `AbsolutePathBuf::join()` instead of re-absolutizing derived
absolute paths.

codex-rs/core-plugins/src/loader.rs

@@ -129,7 +129,7 @@ pub fn refresh_curated_plugin_cache(
     plugin_version: &str,
     configured_curated_plugin_ids: &[PluginId],
 ) -> Result<bool, String> {
-    let store = PluginStore::new(codex_home.to_path_buf());
+    let store = PluginStore::try_new(codex_home.to_path_buf()).map_err(|err| err.to_string())?;
     let curated_marketplace_path = AbsolutePathBuf::try_from(
         codex_home
             .join(".tmp/plugins")
@@ -234,7 +234,7 @@ fn refresh_non_curated_plugin_cache_with_mode(
         .map(PluginId::as_key)
         .collect::<HashSet<_>>();
 
-    let store = PluginStore::new(codex_home.to_path_buf());
+    let store = PluginStore::try_new(codex_home.to_path_buf()).map_err(|err| err.to_string())?;
     let marketplace_outcome = list_marketplaces(additional_roots)
         .map_err(|err| format!("failed to discover marketplaces for cache refresh: {err}"))?;
     let mut plugin_sources = HashMap::<String, MarketplacePluginSource>::new();
@@ -742,7 +742,13 @@ pub async fn installed_plugin_telemetry_metadata(
     codex_home: &Path,
     plugin_id: &PluginId,
 ) -> PluginTelemetryMetadata {
-    let store = PluginStore::new(codex_home.to_path_buf());
+    let store = match PluginStore::try_new(codex_home.to_path_buf()) {
+        Ok(store) => store,
+        Err(err) => {
+            warn!("failed to resolve plugin cache root: {err}");
+            return PluginTelemetryMetadata::from_plugin_id(plugin_id);
+        }
+    };
     let Some(plugin_root) = store.active_plugin_root(plugin_id) else {
         return PluginTelemetryMetadata::from_plugin_id(plugin_id);
     };

codex-rs/core-plugins/src/store.rs

@@ -28,10 +28,15 @@ pub struct PluginStore {
 
 impl PluginStore {
     pub fn new(codex_home: PathBuf) -> Self {
-        Self {
-            root: AbsolutePathBuf::try_from(codex_home.join(PLUGINS_CACHE_DIR))
-                .unwrap_or_else(|err| panic!("plugin cache root should be absolute: {err}")),
-        }
+        Self::try_new(codex_home)
+            .unwrap_or_else(|err| panic!("plugin cache root should be absolute: {err}"))
+    }
+
+    pub fn try_new(codex_home: PathBuf) -> Result<Self, PluginStoreError> {
+        let root = AbsolutePathBuf::from_absolute_path_checked(codex_home.join(PLUGINS_CACHE_DIR))
+            .map_err(|err| PluginStoreError::io("failed to resolve plugin cache root", err))?;
+
+        Ok(Self { root })
     }
 
     pub fn root(&self) -> &AbsolutePathBuf {
@@ -39,22 +44,13 @@ impl PluginStore {
     }
 
     pub fn plugin_base_root(&self, plugin_id: &PluginId) -> AbsolutePathBuf {
-        AbsolutePathBuf::try_from(
-            self.root
-                .as_path()
-                .join(&plugin_id.marketplace_name)
-                .join(&plugin_id.plugin_name),
-        )
-        .unwrap_or_else(|err| panic!("plugin cache path should resolve to an absolute path: {err}"))
+        self.root
+            .join(&plugin_id.marketplace_name)
+            .join(&plugin_id.plugin_name)
     }
 
     pub fn plugin_root(&self, plugin_id: &PluginId, plugin_version: &str) -> AbsolutePathBuf {
-        AbsolutePathBuf::try_from(
-            self.plugin_base_root(plugin_id)
-                .as_path()
-                .join(plugin_version),
-        )
-        .unwrap_or_else(|err| panic!("plugin cache path should resolve to an absolute path: {err}"))
+        self.plugin_base_root(plugin_id).join(plugin_version)
     }
 
     pub fn active_plugin_version(&self, plugin_id: &PluginId) -> Option<String> {

codex-rs/core-plugins/src/store_tests.rs

@@ -33,6 +33,18 @@ fn write_plugin(root: &Path, dir_name: &str, manifest_name: &str) {
     );
 }
 
+#[test]
+fn try_new_rejects_relative_codex_home() {
+    let err = PluginStore::try_new(PathBuf::from("relative"))
+        .expect_err("relative codex home should fail");
+    let err = err.to_string().replace('\\', "/");
+
+    assert_eq!(
+        err,
+        "failed to resolve plugin cache root: path is not absolute: relative/plugins/cache"
+    );
+}
+
 #[test]
 fn install_copies_plugin_into_default_marketplace() {
     let tmp = tempdir().unwrap();

codex-rs/utils/absolute-path/src/absolutize.rs

@@ -12,6 +12,10 @@ use std::path::Path;
 use std::path::PathBuf;
 
 pub(super) fn absolutize(path: &Path) -> std::io::Result<PathBuf> {
+    if path.is_absolute() {
+        return Ok(normalize_path(path));
+    }
+
     Ok(absolutize_from(path, &std::env::current_dir()?))
 }
 

codex-rs/utils/absolute-path/src/lib.rs

@@ -328,6 +328,8 @@ mod tests {
     use crate::test_support::test_path_buf;
     use pretty_assertions::assert_eq;
     use std::fs;
+    #[cfg(unix)]
+    use std::process::Command;
     use tempfile::tempdir;
 
     #[test]
@@ -341,6 +343,46 @@ mod tests {
         assert_eq!(abs_path_buf.as_path(), absolute_path.as_path());
     }
 
+    #[cfg(unix)]
+    #[test]
+    fn from_absolute_path_does_not_read_current_dir_when_path_is_absolute() {
+        let status = Command::new(std::env::current_exe().expect("current test binary"))
+            .arg("from_absolute_path_with_removed_current_dir_child")
+            .arg("--ignored")
+            .env("CODEX_ABSOLUTE_PATH_REMOVED_CWD_CHILD", "1")
+            .status()
+            .expect("run child test");
+
+        assert!(status.success());
+    }
+
+    #[cfg(unix)]
+    #[test]
+    #[ignore]
+    fn from_absolute_path_with_removed_current_dir_child() {
+        if std::env::var_os("CODEX_ABSOLUTE_PATH_REMOVED_CWD_CHILD").is_none() {
+            return;
+        }
+
+        let original_cwd = std::env::current_dir().expect("original cwd");
+        let temp_dir = tempdir().expect("temp dir");
+        let removed_cwd = temp_dir.path().to_path_buf();
+        std::env::set_current_dir(&removed_cwd).expect("enter temp dir");
+        std::fs::remove_dir(&removed_cwd).expect("remove current dir");
+        std::env::current_dir().expect_err("current dir should be unavailable");
+
+        let path = AbsolutePathBuf::from_absolute_path(test_path_buf(
+            "/tmp/codex/../codex-home/plugins/cache",
+        ))
+        .expect("absolute path should not require current dir");
+
+        std::env::set_current_dir(original_cwd).expect("restore cwd");
+        assert_eq!(
+            path.as_path(),
+            test_path_buf("/tmp/codex-home/plugins/cache")
+        );
+    }
+
     #[test]
     fn from_absolute_path_checked_rejects_relative_path() {
         let err = AbsolutePathBuf::from_absolute_path_checked("relative/path")