fix: align spawn user manifest env overlay

crates/manifest/src/cascade.rs

@@ -3,7 +3,8 @@
 //! Pod manifests are assembled from up to three on-disk layers (see
 //! `pod::PodFactory` for the full cascade story):
 //!
-//! 1. **User manifest** — see [`crate::paths::user_manifest_path`]
+//! 1. **User manifest** — Pod CLI uses
+//!    [`crate::paths::user_manifest_path_with_env_override`]
 //! 2. **Project manifest** at the closest `.insomnia/manifest.toml`
 //!    found by walking up from a starting directory (typically `cwd`)
 //! 3. **Programmatic overlay** supplied at the call site

crates/manifest/src/lib.rs

@@ -13,7 +13,9 @@ pub use config::{
 pub use model::{
     AuthRef, ModelCapability, ModelManifest, ReasoningControl, ReasoningEffort, SchemeKind,
 };
-pub use paths::user_manifest_path;
+pub use paths::{
+    user_manifest_path, user_manifest_path_from_env, user_manifest_path_with_env_override,
+};
 pub use protocol::{Permission, ScopeRule};
 pub use scope::{Scope, ScopeError, SharedScope};
 

crates/manifest/src/paths.rs

@@ -23,8 +23,16 @@
 //! 解決された各 base が存在するか / ディレクトリかは保証しない —
 //! 呼び出し側がファイル操作の前に作成 / 検査する。
 
+use std::ffi::OsString;
 use std::path::PathBuf;
 
+/// Environment variable that points at an explicit user manifest.
+///
+/// Pod CLI treats a non-empty value as an explicit manifest path. Empty values
+/// are treated the same as an unset variable, so callers fall back to the
+/// auto-discovered user manifest path.
+pub const USER_MANIFEST_ENV: &str = "INSOMNIA_USER_MANIFEST";
+
 /// 設定ディレクトリ。`manifest.toml`, `providers.toml`, `models.toml`,
 /// `prompts/` などが置かれる。
 pub fn config_dir() -> Option<PathBuf> {
@@ -69,11 +77,38 @@ pub fn runtime_dir() -> Option<PathBuf> {
 
 // ---- well-known file getters ------------------------------------------------
 
-/// `<config_dir>/manifest.toml` — user manifest。
+/// `<config_dir>/manifest.toml` — user manifest の既定位置。
+///
+/// This deliberately ignores [`USER_MANIFEST_ENV`]. Use
+/// [`user_manifest_path_with_env_override`] when mirroring the Pod CLI cascade
+/// resolution rules.
 pub fn user_manifest_path() -> Option<PathBuf> {
     Some(config_dir()?.join("manifest.toml"))
 }
 
+/// Resolve an explicit user manifest override from an env value.
+///
+/// Non-empty values are paths. `None` and empty strings are both treated as no
+/// override, matching the Pod CLI's `INSOMNIA_USER_MANIFEST` handling.
+pub fn user_manifest_path_from_env(value: Option<OsString>) -> Option<PathBuf> {
+    value.and_then(|value| {
+        if value.as_os_str().is_empty() {
+            None
+        } else {
+            Some(PathBuf::from(value))
+        }
+    })
+}
+
+/// User manifest path using the same env override rule as the Pod CLI cascade.
+///
+/// A non-empty [`USER_MANIFEST_ENV`] value wins. If the variable is unset or
+/// empty, this falls back to [`user_manifest_path`]. The returned path is not
+/// guaranteed to exist.
+pub fn user_manifest_path_with_env_override() -> Option<PathBuf> {
+    user_manifest_path_from_env(std::env::var_os(USER_MANIFEST_ENV)).or_else(user_manifest_path)
+}
+
 /// `<config_dir>/prompts/` — user prompts ライブラリ。
 pub fn user_prompts_dir() -> Option<PathBuf> {
     Some(config_dir()?.join("prompts"))
@@ -156,6 +191,7 @@ mod tests {
                 "INSOMNIA_CONFIG_DIR",
                 "INSOMNIA_DATA_DIR",
                 "INSOMNIA_RUNTIME_DIR",
+                "INSOMNIA_USER_MANIFEST",
                 "INSOMNIA_HOME",
                 "XDG_CONFIG_HOME",
                 "XDG_RUNTIME_DIR",
@@ -281,6 +317,37 @@ mod tests {
         assert!(runtime_dir().is_none());
     }
 
+    #[test]
+    fn user_manifest_env_override_wins_when_non_empty() {
+        let _g = EnvGuard::new(&[
+            ("HOME", Some("/h")),
+            ("INSOMNIA_USER_MANIFEST", Some("/tmp/user.toml")),
+        ]);
+        assert_eq!(
+            user_manifest_path_with_env_override().unwrap(),
+            PathBuf::from("/tmp/user.toml")
+        );
+    }
+
+    #[test]
+    fn empty_user_manifest_env_falls_back_to_default_path() {
+        let _g = EnvGuard::new(&[("HOME", Some("/h")), ("INSOMNIA_USER_MANIFEST", Some(""))]);
+        assert_eq!(
+            user_manifest_path_with_env_override().unwrap(),
+            PathBuf::from("/h/.config/insomnia/manifest.toml")
+        );
+    }
+
+    #[test]
+    fn user_manifest_path_from_env_treats_empty_as_unset() {
+        assert_eq!(user_manifest_path_from_env(None), None);
+        assert_eq!(user_manifest_path_from_env(Some(OsString::from(""))), None);
+        assert_eq!(
+            user_manifest_path_from_env(Some(OsString::from("/tmp/u.toml"))).unwrap(),
+            PathBuf::from("/tmp/u.toml")
+        );
+    }
+
     #[test]
     fn well_known_files_compose_off_base_dirs() {
         let _g = EnvGuard::new(&[("INSOMNIA_HOME", Some("/sand"))]);