feat: migrate to new constraint-based loading strategy

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -208,6 +208,7 @@ v2_enum_from_core!(
     }
 );
 
+// TODO(mbolin): Support in-repo layer.
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
 #[serde(tag = "type", rename_all = "camelCase")]
 #[ts(tag = "type")]
@@ -216,17 +217,59 @@ pub enum ConfigLayerSource {
     /// Managed preferences layer delivered by MDM (macOS only).
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
-    Mdm { domain: String, key: String },
+    Mdm {
+        domain: String,
+        key: String,
+    },
+
     /// Managed config layer from a file (usually `managed_config.toml`).
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
-    System { file: AbsolutePathBuf },
-    /// Session-layer overrides supplied via `-c`/`--config`.
-    SessionFlags,
-    /// User config layer from a file (usually `config.toml`).
+    System {
+        file: AbsolutePathBuf,
+    },
+
+    /// User config layer from $CODEX_HOME/config.toml. This layer is special
+    /// in that it is expected to be:
+    /// - writable by the user
+    /// - generally outside the workspace directory
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
-    User { file: AbsolutePathBuf },
+    User {
+        file: AbsolutePathBuf,
+    },
+
+    /// Session-layer overrides supplied via `-c`/`--config`.
+    SessionFlags,
+
+    /// `managed_config.toml` was designed to be a config that was loaded
+    /// as the last layer on top of everything else. This scheme did not quite
+    /// work out as intended, but we keep this variant as a "best effort" while
+    /// we phase out `managed_config.toml` in favor of `requirements.toml`.
+    LegacyManagedConfigTomlFromFile {
+        file: AbsolutePathBuf,
+    },
+
+    LegacyManagedConfigTomlFromMdm,
+}
+
+impl ConfigLayerSource {
+    pub fn precedence(&self) -> i16 {
+        match self {
+            ConfigLayerSource::Mdm { .. } => 0,
+            ConfigLayerSource::System { .. } => 10,
+            ConfigLayerSource::User { .. } => 20,
+            ConfigLayerSource::SessionFlags => 30,
+            ConfigLayerSource::LegacyManagedConfigTomlFromFile { .. } => 40,
+            ConfigLayerSource::LegacyManagedConfigTomlFromMdm => 50,
+        }
+    }
+}
+
+impl PartialOrd for ConfigLayerSource {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.precedence().cmp(&other.precedence()))
+    }
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Default, JsonSchema, TS)]
@@ -344,7 +387,7 @@ pub struct ConfigWriteResponse {
     pub status: WriteStatus,
     pub version: String,
     /// Canonical path to the config file that was written.
-    pub file_path: String,
+    pub file_path: AbsolutePathBuf,
     pub overridden_metadata: Option<OverriddenMetadata>,
 }
 
@@ -357,6 +400,7 @@ pub enum ConfigWriteErrorCode {
     ConfigValidationError,
     ConfigPathNotFound,
     ConfigSchemaUnknownKey,
+    UserLayerNotFound,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]