Enable MCP tool hooks in Codex sessions (#39296)

## What changed

- Execute `mcp_tool` hook handlers through the session's shared MCP runtime, including managed hook configurations.
- Restrict hook calls to already-connected, cataloged, and policy-allowed tools. Unavailable servers fail immediately without starting or reconnecting them.
- Pass session metadata to hook tools, cap hook timeouts by the server timeout, and invoke hooks without model-tool approval or recursive hook dispatch.
- Record handler type and execution mode in hook telemetry, and mark memory as externally influenced after successful or blocking MCP hooks when configured.

## Testing

- Added end-to-end coverage for prompt interpolation, hidden tools, blocking decisions, unavailable servers, thread metadata, approval bypass, and memory-mode handling.
- Added MCP runtime coverage for startup readiness, tool filters, catalog revisions, and managed connector policy.

GitOrigin-RevId: 1647cb801ebc5fa385c7bda9d9c266a389c611b8

codex-rs/core/src/lib.rs

@@ -61,6 +61,7 @@ mod exec_policy;
 #[cfg(test)]
 mod git_info_tests;
 mod guardian;
+mod hook_mcp_executor;
 mod hook_runtime;
 mod image_preparation;
 mod installation_id;