Move marketplace add under plugin command (#18116)

## Summary
- move the marketplace add CLI from `codex marketplace add` to `codex
plugin marketplace add`
- keep marketplace config overrides working through the nested plugin
command
- reject `--sparse` for local marketplace directory sources before the
local-source install path bypasses git-source validation

## Validation
- `just fmt`
- `git diff --check`
- `cargo test -p codex-cli`
- `cargo test -p codex-core marketplace_add -- --nocapture`
- `cargo test -p codex-core
install_plugin_updates_config_with_relative_path_and_plugin_key --
--nocapture`
- `xli-test-marketplace-cli` local isolated matrix: `T1`, `L1`-`L10`

codex-rs/cli/tests/marketplace_add.rs

@@ -48,7 +48,7 @@ async fn marketplace_add_local_directory_source() -> Result<()> {
 
     codex_command(codex_home.path())?
         .current_dir(source_parent)
-        .args(["marketplace", "add", source_arg.as_str()])
+        .args(["plugin", "marketplace", "add", source_arg.as_str()])
         .assert()
         .success();
 
@@ -78,7 +78,12 @@ async fn marketplace_add_rejects_local_manifest_file_source() -> Result<()> {
     let manifest_path = source.path().join(".agents/plugins/marketplace.json");
 
     codex_command(codex_home.path())?
-        .args(["marketplace", "add", manifest_path.to_str().unwrap()])
+        .args([
+            "plugin",
+            "marketplace",
+            "add",
+            manifest_path.to_str().unwrap(),
+        ])
         .assert()
         .failure()
         .stderr(contains(
@@ -87,3 +92,27 @@ async fn marketplace_add_rejects_local_manifest_file_source() -> Result<()> {
 
     Ok(())
 }
+
+#[tokio::test]
+async fn marketplace_add_rejects_sparse_for_local_directory_source() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let source = TempDir::new()?;
+    write_marketplace_source(source.path(), "local ref")?;
+
+    codex_command(codex_home.path())?
+        .args([
+            "plugin",
+            "marketplace",
+            "add",
+            "--sparse",
+            ".agents",
+            source.path().to_str().unwrap(),
+        ])
+        .assert()
+        .failure()
+        .stderr(contains(
+            "--sparse is only supported for git marketplace sources",
+        ));
+
+    Ok(())
+}

codex-rs/cli/tests/marketplace_upgrade.rs

@@ -0,0 +1,36 @@
+use anyhow::Result;
+use predicates::str::contains;
+use std::path::Path;
+use tempfile::TempDir;
+
+fn codex_command(codex_home: &Path) -> Result<assert_cmd::Command> {
+    let mut cmd = assert_cmd::Command::new(codex_utils_cargo_bin::cargo_bin("codex")?);
+    cmd.env("CODEX_HOME", codex_home);
+    Ok(cmd)
+}
+
+#[tokio::test]
+async fn marketplace_upgrade_runs_under_plugin() -> Result<()> {
+    let codex_home = TempDir::new()?;
+
+    codex_command(codex_home.path())?
+        .args(["plugin", "marketplace", "upgrade"])
+        .assert()
+        .success()
+        .stdout(contains("No configured Git marketplaces to upgrade."));
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn marketplace_upgrade_no_longer_runs_at_top_level() -> Result<()> {
+    let codex_home = TempDir::new()?;
+
+    codex_command(codex_home.path())?
+        .args(["marketplace", "upgrade"])
+        .assert()
+        .failure()
+        .stderr(contains("unexpected argument 'upgrade' found"));
+
+    Ok(())
+}