Add marketplace command (#17087)

Added a new top-level `codex marketplace add` command for installing
plugin marketplaces into Codex’s local marketplace cache.

This change adds source parsing for local directories, GitHub shorthand,
and git URLs, supports optional `--ref` and git-only `--sparse` checkout
paths, stages the source in a temp directory, validates the marketplace
manifest, and installs it under
`$CODEX_HOME/marketplaces/<marketplace-name>`

Included tests cover local install behavior in the CLI and marketplace
discovery from installed roots in core. Scoped formatting and fix passes
were run, and targeted CLI/core tests passed.

codex-rs/cli/tests/marketplace_add.rs

@@ -0,0 +1,60 @@
+use anyhow::Result;
+use codex_core::plugins::marketplace_install_root;
+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)
+}
+
+fn write_marketplace_source(source: &Path, marker: &str) -> Result<()> {
+    std::fs::create_dir_all(source.join(".agents/plugins"))?;
+    std::fs::create_dir_all(source.join("plugins/sample/.codex-plugin"))?;
+    std::fs::write(
+        source.join(".agents/plugins/marketplace.json"),
+        r#"{
+  "name": "debug",
+  "plugins": [
+    {
+      "name": "sample",
+      "source": {
+        "source": "local",
+        "path": "./plugins/sample"
+      }
+    }
+  ]
+}"#,
+    )?;
+    std::fs::write(
+        source.join("plugins/sample/.codex-plugin/plugin.json"),
+        r#"{"name":"sample"}"#,
+    )?;
+    std::fs::write(source.join("plugins/sample/marker.txt"), marker)?;
+    Ok(())
+}
+
+#[tokio::test]
+async fn marketplace_add_rejects_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(["marketplace", "add", source.path().to_str().unwrap()])
+        .assert()
+        .failure()
+        .stderr(contains(
+            "local marketplace sources are not supported yet; use an HTTP(S) Git URL, SSH Git URL, or GitHub owner/repo",
+        ));
+
+    assert!(
+        !marketplace_install_root(codex_home.path())
+            .join("debug")
+            .exists()
+    );
+
+    Ok(())
+}