* feat(tools): add tool_search for deferred MCP tool loading
When multiple MCP servers are enabled, total tool count can exceed 30-50,
causing context bloat and degraded tool selection accuracy. This adds a
deferred tool loading mechanism controlled by `tool_search.enabled` config.
- Add ToolSearchConfig with single `enabled` field
- Add DeferredToolRegistry with regex search (select:, +keyword, keyword)
- Add tool_search tool returning OpenAI-compatible function JSON
- Add DeferredToolFilterMiddleware to hide deferred schemas from bind_tools
- Add <available-deferred-tools> section to system prompt
- Enable MCP tool_name_prefix to prevent cross-server name collisions
- Add 34 unit tests covering registry, tool, prompt, and middleware
* fix: reset stale deferred registry and bump config_version
- Reset deferred registry upfront in get_available_tools() to prevent
stale tool entries when MCP servers are disabled between calls
- Bump config_version to 2 for new tool_search config field
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
* fix(tests): mock get_app_config in prompt section tests for CI
CI has no config.yaml, causing TestDeferredToolsPromptSection to fail
with FileNotFoundError. Add autouse fixture to mock get_app_config.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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