[plugins] Expose marketplace source in marketplace list JSON (#27009)

## Summary
- Follow-up to #26417 and #26631
- Add `marketplaceSource` to `codex plugin marketplace list --json`
entries for configured marketplaces
- Reuse the existing `marketplaceSource` shape from `codex plugin list
--json`
- Keep human-readable marketplace list output unchanged
- Add CLI coverage for configured local and git marketplace sources

Example:

```json
{
  "marketplaces": [
    {
      "name": "debug",
      "root": "/path/to/.codex/.tmp/marketplaces/debug",
      "marketplaceSource": {
        "sourceType": "git",
        "source": "https://example.com/acme/agent-skills.git"
      }
    }
  ]
}
```

## Validation
- `just fmt`
- `just fix -p codex-cli`
- `just test -p codex-cli marketplace_list`
- `just test -p codex-cli`

codex-rs/cli/tests/plugin_cli.rs

@@ -341,6 +341,7 @@ async fn marketplace_list_shows_configured_marketplace_names() -> Result<()> {
 #[tokio::test]
 async fn marketplace_list_json_prints_configured_marketplaces() -> Result<()> {
     let (codex_home, source) = setup_local_marketplace()?;
+    let source_path = source.path().display().to_string();
 
     let assert = codex_command(codex_home.path())?
         .args(["plugin", "marketplace", "list", "--json"])
@@ -355,7 +356,112 @@ async fn marketplace_list_json_prints_configured_marketplaces() -> Result<()> {
             "marketplaces": [
                 {
                     "name": "debug",
-                    "root": source.path().display().to_string(),
+                    "root": source_path,
+                    "marketplaceSource": {
+                        "sourceType": "local",
+                        "source": source_path,
+                    },
+                },
+            ],
+        })
+    );
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn marketplace_list_json_includes_configured_git_marketplace_source() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let marketplace_root = codex_home
+        .path()
+        .join(".tmp")
+        .join("marketplaces")
+        .join("debug");
+    write_plugins_enabled_config(codex_home.path())?;
+    write_marketplace_source(&marketplace_root)?;
+    let update = MarketplaceConfigUpdate {
+        last_updated: "2026-06-04T08:39:49Z",
+        last_revision: Some("abc123"),
+        source_type: "git",
+        source: "https://example.com/acme/agent-skills.git",
+        ref_name: None,
+        sparse_paths: &[],
+    };
+    record_user_marketplace(codex_home.path(), "debug", &update)?;
+    let normalized_root = canonicalize_existing_preserving_symlinks(&marketplace_root)?;
+
+    let assert = codex_command(codex_home.path())?
+        .args(["plugin", "marketplace", "list", "--json"])
+        .assert()
+        .success();
+    let stdout = assert.get_output().stdout.as_slice();
+    let actual: serde_json::Value = serde_json::from_slice(stdout)?;
+
+    assert_eq!(
+        actual,
+        json!({
+            "marketplaces": [
+                {
+                    "name": "debug",
+                    "root": normalized_root.display().to_string(),
+                    "marketplaceSource": {
+                        "sourceType": "git",
+                        "source": "https://example.com/acme/agent-skills.git",
+                    },
+                },
+            ],
+        })
+    );
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn marketplace_list_json_keys_configured_source_by_root() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let home = TempDir::new()?;
+    let marketplace_root = codex_home
+        .path()
+        .join(".tmp")
+        .join("marketplaces")
+        .join("debug");
+    write_plugins_enabled_config(codex_home.path())?;
+    write_marketplace_source(home.path())?;
+    write_marketplace_source(&marketplace_root)?;
+    let update = MarketplaceConfigUpdate {
+        last_updated: "2026-06-04T08:39:49Z",
+        last_revision: Some("abc123"),
+        source_type: "git",
+        source: "https://example.com/acme/agent-skills.git",
+        ref_name: None,
+        sparse_paths: &[],
+    };
+    record_user_marketplace(codex_home.path(), "debug", &update)?;
+    let normalized_root = canonicalize_existing_preserving_symlinks(&marketplace_root)?;
+
+    let assert = codex_command(codex_home.path())?
+        .env("HOME", home.path())
+        .args(["plugin", "marketplace", "list", "--json"])
+        .assert()
+        .success();
+    let stdout = assert.get_output().stdout.as_slice();
+    let actual: serde_json::Value = serde_json::from_slice(stdout)?;
+
+    assert_eq!(
+        actual,
+        json!({
+            "marketplaces": [
+                {
+                    "name": "debug",
+                    "root": home.path().display().to_string(),
+                },
+                {
+                    "name": "debug",
+                    "root": normalized_root.display().to_string(),
+                    "marketplaceSource": {
+                        "sourceType": "git",
+                        "source": "https://example.com/acme/agent-skills.git",
+                    },
                 },
             ],
         })