Add JSON output for plugin subcommands (#26631)

## Summary
- Follow-up to #25330 and #26417
- Add `--json` output for `codex plugin add` and `codex plugin remove`
- Add `--json` output for `codex plugin marketplace
add/list/upgrade/remove`
- Keep existing human-readable output unchanged
- Keep existing error handling/stderr behavior unchanged; `--json`
changes successful stdout output only
- Align marketplace add/remove JSON field names with the existing
app-server protocol shape
- Add CLI coverage for plugin and marketplace JSON outputs

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

codex-rs/cli/src/plugin_cmd.rs

@@ -6,6 +6,7 @@ use codex_core::config::Config;
 use codex_core::config::find_codex_home;
 use codex_core_plugins::ConfiguredMarketplace;
 use codex_core_plugins::OPENAI_BUNDLED_MARKETPLACE_NAME;
+use codex_core_plugins::PluginInstallOutcome;
 use codex_core_plugins::PluginInstallRequest;
 use codex_core_plugins::PluginsConfigInput;
 use codex_core_plugins::PluginsManager;
@@ -73,6 +74,10 @@ pub struct AddPluginArgs {
     /// Configured marketplace name to use when PLUGIN does not include @MARKETPLACE.
     #[arg(long = "marketplace", short = 'm', value_name = "MARKETPLACE")]
     marketplace_name: Option<String>,
+
+    /// Output install result as JSON.
+    #[arg(long = "json")]
+    json: bool,
 }
 
 #[derive(Debug, Parser)]
@@ -107,6 +112,10 @@ pub struct RemovePluginArgs {
     /// Marketplace name to use when PLUGIN does not include @MARKETPLACE.
     #[arg(long = "marketplace", short = 'm', value_name = "MARKETPLACE")]
     marketplace_name: Option<String>,
+
+    /// Output remove result as JSON.
+    #[arg(long = "json")]
+    json: bool,
 }
 
 pub async fn run_plugin_add(
@@ -118,11 +127,16 @@ pub async fn run_plugin_add(
         plugins_input,
         manager,
     } = load_plugin_command_context(overrides).await?;
+    let AddPluginArgs {
+        plugin,
+        marketplace_name,
+        json,
+    } = args;
     let PluginSelection {
         plugin_name,
         marketplace_name,
         ..
-    } = parse_plugin_selection(args.plugin, args.marketplace_name)?;
+    } = parse_plugin_selection(plugin, marketplace_name)?;
     let marketplace = find_marketplace_for_plugin(
         &manager,
         codex_home.as_path(),
@@ -137,6 +151,12 @@ pub async fn run_plugin_add(
         })
         .await?;
 
+    if json {
+        let output = JsonPluginAddOutput::from_outcome(outcome);
+        println!("{}", serde_json::to_string_pretty(&output)?);
+        return Ok(());
+    }
+
     println!(
         "Added plugin `{}` from marketplace `{}`.",
         outcome.plugin_id.plugin_name, outcome.plugin_id.marketplace_name
@@ -149,6 +169,30 @@ pub async fn run_plugin_add(
     Ok(())
 }
 
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct JsonPluginAddOutput {
+    plugin_id: String,
+    name: String,
+    marketplace_name: String,
+    version: String,
+    installed_path: String,
+    auth_policy: &'static str,
+}
+
+impl JsonPluginAddOutput {
+    fn from_outcome(outcome: PluginInstallOutcome) -> Self {
+        Self {
+            plugin_id: outcome.plugin_id.as_key(),
+            name: outcome.plugin_id.plugin_name,
+            marketplace_name: outcome.plugin_id.marketplace_name,
+            version: outcome.plugin_version,
+            installed_path: outcome.installed_path.as_path().display().to_string(),
+            auth_policy: auth_policy_label(outcome.auth_policy),
+        }
+    }
+}
+
 pub async fn run_plugin_list(
     overrides: Vec<(String, toml::Value)>,
     args: ListPluginsArgs,
@@ -449,9 +493,22 @@ pub async fn run_plugin_remove(
     args: RemovePluginArgs,
 ) -> Result<()> {
     let PluginCommandContext { manager, .. } = load_plugin_command_context(overrides).await?;
-    let selection = parse_plugin_selection(args.plugin, args.marketplace_name)?;
+    let RemovePluginArgs {
+        plugin,
+        marketplace_name,
+        json,
+    } = args;
+    let selection = parse_plugin_selection(plugin, marketplace_name)?;
+
+    manager
+        .uninstall_plugin(selection.plugin_key.clone())
+        .await?;
+    if json {
+        let output = JsonPluginRemoveOutput::from_selection(selection);
+        println!("{}", serde_json::to_string_pretty(&output)?);
+        return Ok(());
+    }
 
-    manager.uninstall_plugin(selection.plugin_key).await?;
     println!(
         "Removed plugin `{}` from marketplace `{}`.",
         selection.plugin_name, selection.marketplace_name
@@ -460,6 +517,24 @@ pub async fn run_plugin_remove(
     Ok(())
 }
 
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct JsonPluginRemoveOutput {
+    plugin_id: String,
+    name: String,
+    marketplace_name: String,
+}
+
+impl JsonPluginRemoveOutput {
+    fn from_selection(selection: PluginSelection) -> Self {
+        Self {
+            plugin_id: selection.plugin_key,
+            name: selection.plugin_name,
+            marketplace_name: selection.marketplace_name,
+        }
+    }
+}
+
 struct PluginCommandContext {
     codex_home: PathBuf,
     plugins_input: PluginsConfigInput,