Apps instructions refer to nonexistent `tools_search` tool name

Summary

The Codex Apps/Connectors instruction fragment refers to tools_search (plural), although the actual Codex tool is tool_search (singular).

Evidence

In codex-rs/core/src/context/apps_instructions.rs, the generated developer text says:

An installed app's MCP tools are either provided to you already, or can be lazy-loaded through the `tool_search` tool. If `tool_search` is available, the apps that are searchable by `tools_search` will be listed by it.

The Codex implementation and handler are named tool_search, including:

• codex-rs/tools/src/tool_search.rs
• codex-rs/core/src/tools/handlers/tool_search.rs
• codex-rs/core/src/tools/handlers/tool_search_spec.rs

The same typo is present in the Apps instructions snapshot tests, so the current test fixture preserves it.

Impact

This is primarily a model-facing documentation/prompt defect. It introduces a reference to a tool name that does not match the actual tool name and may cause the model to look for or attempt to invoke tools_search. It also makes the Apps tool-discovery instructions internally inconsistent.

Expected behavior

The Apps instructions should use the actual tool name consistently:

If `tool_search` is available, the apps that are searchable by `tool_search` will be listed by it.

Suggested fix

1. Replace tools_search with tool_search in codex-rs/core/src/context/apps_instructions.rs.
2. Update the corresponding snapshot fixture.
3. Add or retain a test that checks the generated Apps instructions use the canonical tool name.

Reproduction

1. Run Codex with Apps/Connectors instructions enabled.
2. Inspect the generated <apps_instructions> developer block.
3. Observe tool_search in the first reference and tools_search in the second reference.