Use MCP server instructions in deferred namespace descriptions

[sayan-oai]

Why

MCP servers can provide instructions that explain what their tools are for. Directly exposed MCP namespaces already use those instructions when a connector description is not available, but deferred tool_search results did not preserve that fallback. The direct path falls back from connector metadata to server instructions, while the deferred path only carried connector_description and otherwise fell back to generic namespace text.

That meant a plain MCP server could provide useful model-facing guidance and still appear as Tools in the X namespace. whenever it was discovered lazily through tool_search.

What changed

• Store one model-facing namespace_description on ToolInfo, using connector descriptions for connector-backed tools and server instructions for plain MCP servers.
• Thread that namespace description through the tool_search source list, search indexing, and returned namespace metadata.
• Add an end-to-end regression test for deferred non-app MCP search results exposing server instructions as the namespace description.

Verification

• cargo test -p codex-tools search_tool_description_lists_each_mcp_source_once --lib
• cargo test -p codex-core --test all tool_search_uses_non_app_mcp_server_instructions_as_namespace_description

[pakrym-oai]

is connector_description used in any other interesting way? can we have one fied?

[sayan-oai]

fair, i think we can