Auto-upgrade configured marketplaces (#17425)

## Summary
- Add best-effort auto-upgrade for user-configured Git marketplaces
recorded in `config.toml`.
- Track the last activated Git revision with `last_revision` so
unchanged marketplace sources skip clone work.
- Trigger the upgrade from plugin startup and `plugin/list`, while
preserving existing fail-open plugin behavior with warning logs rather
than new user-visible errors.

## Details
- Remote configured marketplaces use `git ls-remote` to compare the
source/ref against the recorded revision.
- Upgrades clone into a staging directory, validate that
`.agents/plugins/marketplace.json` exists and that the manifest name
matches the configured marketplace key, then atomically activate the new
root.
- Local `.agents/plugins/marketplace.json` marketplaces remain live
filesystem state and are not auto-pulled.
- Existing non-curated plugin cache refresh is kicked after successful
marketplace root upgrades.

## Validation
- `just write-config-schema`
- `cargo test -p codex-core marketplace_upgrade`
- `cargo check -p codex-cli -p codex-app-server`
- `just fix -p codex-core`

Did not run the complete `cargo test` suite because the repo
instructions require asking before a full core workspace run.

codex-rs/core-plugins/src/loader.rs

@@ -41,6 +41,12 @@ const DEFAULT_APP_CONFIG_FILE: &str = ".app.json";
 const OPENAI_CURATED_MARKETPLACE_NAME: &str = "openai-curated";
 const CONFIG_TOML_FILE: &str = "config.toml";
 
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum NonCuratedCacheRefreshMode {
+    IfVersionChanged,
+    ForceReinstall,
+}
+
 pub fn log_plugin_load_errors(outcome: &PluginLoadOutcome<McpServerConfig>) {
     for plugin in outcome
         .plugins()
@@ -180,6 +186,29 @@ pub fn refresh_curated_plugin_cache(
 pub fn refresh_non_curated_plugin_cache(
     codex_home: &Path,
     additional_roots: &[AbsolutePathBuf],
+) -> Result<bool, String> {
+    refresh_non_curated_plugin_cache_with_mode(
+        codex_home,
+        additional_roots,
+        NonCuratedCacheRefreshMode::IfVersionChanged,
+    )
+}
+
+pub fn refresh_non_curated_plugin_cache_force_reinstall(
+    codex_home: &Path,
+    additional_roots: &[AbsolutePathBuf],
+) -> Result<bool, String> {
+    refresh_non_curated_plugin_cache_with_mode(
+        codex_home,
+        additional_roots,
+        NonCuratedCacheRefreshMode::ForceReinstall,
+    )
+}
+
+fn refresh_non_curated_plugin_cache_with_mode(
+    codex_home: &Path,
+    additional_roots: &[AbsolutePathBuf],
+    mode: NonCuratedCacheRefreshMode,
 ) -> Result<bool, String> {
     let configured_non_curated_plugin_ids =
         non_curated_plugin_ids_from_config_keys(configured_plugins_from_codex_home(
@@ -248,7 +277,9 @@ pub fn refresh_non_curated_plugin_cache(
             continue;
         };
 
-        if store.active_plugin_version(&plugin_id).as_deref() == Some(plugin_version.as_str()) {
+        if mode == NonCuratedCacheRefreshMode::IfVersionChanged
+            && store.active_plugin_version(&plugin_id).as_deref() == Some(plugin_version.as_str())
+        {
             continue;
         }