Extract plugin loading and marketplace logic into codex-core-plugins (#18070)

Split plugin loading, marketplace, and related infrastructure out of
core into codex-core-plugins, while keeping the core-facing
configuration and orchestration flow in codex-core.

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/Cargo.lock

@@ -1446,6 +1446,7 @@ dependencies = [
  "codex-cloud-requirements",
  "codex-config",
  "codex-core",
+ "codex-core-plugins",
  "codex-exec-server",
  "codex-features",
  "codex-feedback",
@@ -1913,6 +1914,7 @@ dependencies = [
  "codex-code-mode",
  "codex-config",
  "codex-connectors",
+ "codex-core-plugins",
  "codex-core-skills",
  "codex-exec-server",
  "codex-execpolicy",
@@ -2013,6 +2015,33 @@ dependencies = [
  "zstd 0.13.3",
 ]
 
+[[package]]
+name = "codex-core-plugins"
+version = "0.0.0"
+dependencies = [
+ "codex-app-server-protocol",
+ "codex-config",
+ "codex-core-skills",
+ "codex-exec-server",
+ "codex-git-utils",
+ "codex-login",
+ "codex-plugin",
+ "codex-protocol",
+ "codex-utils-absolute-path",
+ "codex-utils-plugins",
+ "dirs",
+ "pretty_assertions",
+ "reqwest",
+ "serde",
+ "serde_json",
+ "tempfile",
+ "thiserror 2.0.18",
+ "tokio",
+ "toml 0.9.11+spec-1.1.0",
+ "tracing",
+ "url",
+]
+
 [[package]]
 name = "codex-core-skills"
 version = "0.0.0"