Add a connector declaration snapshot (#29851)

## Why

Connector declarations currently enter Codex through broad plugin
capability summaries, then MCP setup, turn tooling, and `app/list` each
reconstruct the same information. That makes executor-selected
connectors difficult to add without coupling connector behavior to the
host plugin loader.

This PR introduces a small connector-owned value that later stack layers
can populate before thread startup.

## What changed

- Move the pure app-declaration parser into `codex-connectors`,
preserving declaration order and category cleanup while leaving
host-side validation and deduplication unchanged.
- Add an immutable `ConnectorSnapshot` with ordered connector IDs and
plugin display-name provenance.
- Adapt the existing local-plugin capability summaries into that
snapshot at current consumer boundaries.
- Use the snapshot for MCP tool provenance, turn connector inventory,
and `app/list`.
- Keep the crate API narrow: no test-only snapshot accessors are
exposed.

The externally visible behavior is unchanged. Connector tools still come
from the orchestrator-owned `/ps/mcp` server, and local plugin
enablement remains owned by the existing plugin loader.

## Stack scope

This is the foundation only. It does not read selected executor packages
or change thread startup. #29852 adds the executor-backed declaration
reader, and #29856 composes selected declarations into a thread
snapshot.

codex-rs/codex-mcp/src/mcp/mod.rs

@@ -24,8 +24,8 @@ use codex_config::McpServerTransportConfig;
 use codex_config::types::AppToolApproval;
 use codex_config::types::AuthKeyringBackendKind;
 use codex_config::types::OAuthCredentialsStoreMode;
+use codex_connectors::ConnectorSnapshot;
 use codex_login::CodexAuth;
-use codex_plugin::PluginCapabilitySummary;
 use codex_protocol::mcp::McpServerInfo;
 use codex_protocol::mcp::Resource;
 use codex_protocol::mcp::ResourceTemplate;
@@ -142,9 +142,9 @@ pub struct McpConfig {
     pub client_elicitation_capability: ElicitationCapability,
     /// Resolved MCP registrations keyed by logical server name.
     pub mcp_server_catalog: ResolvedMcpCatalog,
-    /// Plugin metadata used to attribute connector tools to plugin display names.
+    /// Plugin declarations used to attribute connector tools to plugin display names.
     /// MCP registrations retain their own package attribution in the catalog.
-    pub plugin_capability_summaries: Vec<PluginCapabilitySummary>,
+    pub connector_snapshot: ConnectorSnapshot,
 }
 
 #[derive(Debug, Clone, Default, PartialEq, Eq)]
@@ -182,14 +182,16 @@ impl ToolPluginProvenance {
 
     fn from_config(config: &McpConfig) -> Self {
         let mut tool_plugin_provenance = Self::default();
-        for plugin in &config.plugin_capability_summaries {
-            for connector_id in &plugin.app_connector_ids {
-                tool_plugin_provenance
-                    .plugin_display_names_by_connector_id
-                    .entry(connector_id.0.clone())
-                    .or_default()
-                    .push(plugin.display_name.clone());
-            }
+        for connector_id in config.connector_snapshot.connector_ids() {
+            tool_plugin_provenance
+                .plugin_display_names_by_connector_id
+                .insert(
+                    connector_id.0.clone(),
+                    config
+                        .connector_snapshot
+                        .plugin_display_names_for_connector_id(&connector_id.0)
+                        .to_vec(),
+                );
         }
 
         for (server_name, attribution) in config