Summary

• mark ToolSearch as removed and ignore stale config writes for its legacy key
• make search tool exposure depend only on model capability, not a feature toggle
• remove app-server enablement support and prune now-obsolete test coverage/setup

Verification

• cargo test -p codex-features
• cargo test -p codex-tools
• cargo test -p codex-core search_tool_requires_model_capability
• cargo test -p codex-app-server experimental_feature_enablement_set_

Notes

• This keeps the legacy config key as a no-op for compatibility while removing the ability to toggle the behavior off cleanly.
• No developer-facing docs update outside the touched app-server README was needed.