bug(runtime): safe-boundary resume rejects Code Mode exec calls #5876

What happened

When a session runs in Code Mode, Runtime replaces the normal provider-visible tool surface with its generated exec tool. Safe-boundary resume currently rebuilds available names from the ordinary Host composer, which omits exec. The planner then parks an otherwise-safe continuation with tool_catalog_mismatch after a completed exec call.

This is a separate instance of the generated-tool catalog mismatch fixed for tool_search in #5872.

How to reproduce

1. Enable Code Mode for a session.
2. Let the model complete an exec call and commit its response.
3. Stop the turn at an otherwise-safe boundary and request resume.
4. Inspect the continuation-plan diagnostics for the missing exec tool.

Expected: resume validation uses the effective Code Mode tool surface, including Runtime-generated exec, and accepts the continuation when the remaining safety checks pass.

Environment

• Maka branch: main
• Surface: TUI / Runtime Host
• Runtime mode: Code Mode