fix: harden plugin feature gating (#15020)

1. Use requirement-resolved config.features as the plugin gate.
2. Guard plugin/list, plugin/read, and related flows behind that gate.
3. Skip bad marketplace.json files instead of failing the whole list.
4. Simplify plugin state and caching.

codex-rs/protocol/src/protocol.rs

@@ -2272,6 +2272,7 @@ pub enum SessionSource {
     VSCode,
     Exec,
     Mcp,
+    Custom(String),
     SubAgent(SubAgentSource),
     #[serde(other)]
     Unknown,
@@ -2302,6 +2303,7 @@ impl fmt::Display for SessionSource {
             SessionSource::VSCode => f.write_str("vscode"),
             SessionSource::Exec => f.write_str("exec"),
             SessionSource::Mcp => f.write_str("mcp"),
+            SessionSource::Custom(source) => f.write_str(source),
             SessionSource::SubAgent(sub_source) => write!(f, "subagent_{sub_source}"),
             SessionSource::Unknown => f.write_str("unknown"),
         }
@@ -2309,6 +2311,23 @@ impl fmt::Display for SessionSource {
 }
 
 impl SessionSource {
+    pub fn from_startup_arg(value: &str) -> Result<Self, &'static str> {
+        let trimmed = value.trim();
+        if trimmed.is_empty() {
+            return Err("session source must not be empty");
+        }
+
+        let normalized = trimmed.to_ascii_lowercase();
+        Ok(match normalized.as_str() {
+            "cli" => SessionSource::Cli,
+            "vscode" => SessionSource::VSCode,
+            "exec" => SessionSource::Exec,
+            "mcp" | "appserver" | "app-server" | "app_server" => SessionSource::Mcp,
+            "unknown" => SessionSource::Unknown,
+            _ => SessionSource::Custom(trimmed.to_string()),
+        })
+    }
+
     pub fn get_nickname(&self) -> Option<String> {
         match self {
             SessionSource::SubAgent(SubAgentSource::ThreadSpawn { agent_nickname, .. }) => {
@@ -2332,6 +2351,25 @@ impl SessionSource {
             _ => None,
         }
     }
+
+    pub fn restriction_product(&self) -> Option<Product> {
+        match self {
+            SessionSource::Custom(source) => Product::from_session_source_name(source),
+            SessionSource::Cli
+            | SessionSource::VSCode
+            | SessionSource::Exec
+            | SessionSource::Mcp
+            | SessionSource::SubAgent(_)
+            | SessionSource::Unknown => Some(Product::Codex),
+        }
+    }
+
+    pub fn matches_product_restriction(&self, products: &[Product]) -> bool {
+        products.is_empty()
+            || self
+                .restriction_product()
+                .is_some_and(|product| products.contains(&product))
+    }
 }
 
 impl fmt::Display for SubAgentSource {
@@ -2923,6 +2961,18 @@ pub enum Product {
     #[serde(alias = "ATLAS")]
     Atlas,
 }
+
+impl Product {
+    pub fn from_session_source_name(value: &str) -> Option<Self> {
+        let normalized = value.trim().to_ascii_lowercase();
+        match normalized.as_str() {
+            "chatgpt" => Some(Self::Chatgpt),
+            "codex" => Some(Self::Codex),
+            "atlas" => Some(Self::Atlas),
+            _ => None,
+        }
+    }
+}
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(rename_all = "snake_case")]
 #[ts(rename_all = "snake_case")]
@@ -3423,6 +3473,92 @@ mod tests {
             .any(|root| root.is_path_writable(path))
     }
 
+    #[test]
+    fn session_source_from_startup_arg_maps_known_values() {
+        assert_eq!(
+            SessionSource::from_startup_arg("vscode").unwrap(),
+            SessionSource::VSCode
+        );
+        assert_eq!(
+            SessionSource::from_startup_arg("app-server").unwrap(),
+            SessionSource::Mcp
+        );
+    }
+
+    #[test]
+    fn session_source_from_startup_arg_preserves_custom_values() {
+        assert_eq!(
+            SessionSource::from_startup_arg("atlas").unwrap(),
+            SessionSource::Custom("atlas".to_string())
+        );
+    }
+
+    #[test]
+    fn session_source_restriction_product_defaults_non_custom_sources_to_codex() {
+        assert_eq!(
+            SessionSource::Cli.restriction_product(),
+            Some(Product::Codex)
+        );
+        assert_eq!(
+            SessionSource::VSCode.restriction_product(),
+            Some(Product::Codex)
+        );
+        assert_eq!(
+            SessionSource::Exec.restriction_product(),
+            Some(Product::Codex)
+        );
+        assert_eq!(
+            SessionSource::Mcp.restriction_product(),
+            Some(Product::Codex)
+        );
+        assert_eq!(
+            SessionSource::SubAgent(SubAgentSource::Review).restriction_product(),
+            Some(Product::Codex)
+        );
+        assert_eq!(
+            SessionSource::Unknown.restriction_product(),
+            Some(Product::Codex)
+        );
+    }
+
+    #[test]
+    fn session_source_restriction_product_maps_custom_sources_to_products() {
+        assert_eq!(
+            SessionSource::Custom("chatgpt".to_string()).restriction_product(),
+            Some(Product::Chatgpt)
+        );
+        assert_eq!(
+            SessionSource::Custom("ATLAS".to_string()).restriction_product(),
+            Some(Product::Atlas)
+        );
+        assert_eq!(
+            SessionSource::Custom("codex".to_string()).restriction_product(),
+            Some(Product::Codex)
+        );
+        assert_eq!(
+            SessionSource::Custom("atlas-dev".to_string()).restriction_product(),
+            None
+        );
+    }
+
+    #[test]
+    fn session_source_matches_product_restriction() {
+        assert!(
+            SessionSource::Custom("chatgpt".to_string())
+                .matches_product_restriction(&[Product::Chatgpt])
+        );
+        assert!(
+            !SessionSource::Custom("chatgpt".to_string())
+                .matches_product_restriction(&[Product::Codex])
+        );
+        assert!(SessionSource::VSCode.matches_product_restriction(&[Product::Codex]));
+        assert!(
+            !SessionSource::Custom("atlas-dev".to_string())
+                .matches_product_restriction(&[Product::Atlas])
+        );
+        assert!(SessionSource::Custom("atlas-dev".to_string()).matches_product_restriction(&[]));
+    }
+
     fn sandbox_policy_probe_paths(policy: &SandboxPolicy, cwd: &Path) -> Vec<PathBuf> {
         let mut paths = vec![cwd.to_path_buf()];
         paths.extend(