fix(agent): connections.save 的 function-calling schema 去掉顶层 oneOf - #245

Description

Fixes the task-level failure Invalid request: OpenAI: Invalid schema for function 'connections_save': schema must have type 'object' and not have 'oneOf'/'anyOf'/'allOf'/'enum'/'const'/'not' at the top level reported by the built-in AI assistant when it tries to save a connection.

Root cause is two-fold:

1. The connections.save tool schema used a top-level oneOf (plus a nested not) to express "create or update". Providers require the tool-parameter schema to be a plain object at the root; a combinator there makes them reject the whole model request, not just this one tool — hence a task-level failure.
2. Our own validate_function_calling_schema only checked that the root was an object and that combinator branches were objects, so it happily let this schema through and the error only surfaced at the provider, where the message names the function but not the tool.

Changes:

• crates/navop_runtime/src/connections.rs: connections.save now exposes a flat object schema. The "omit id to create, pass id + patch to update" contract moved into the schema/field descriptions; the actual either/or rule is still enforced at runtime by ConnectionToolHandler::save branching on id, so behaviour is unchanged.
• crates/agent_runtime/src/tools/spec.rs: the function-calling validator now rejects the provider-unsupported keywords at the root (oneOf/anyOf/allOf/enum/const/not) and reports the tool name plus a JSON pointer. Nested usage (e.g. anyOf inside properties.*) stays allowed.
• Regression tests: connection tool schemas must be provider-safe at the root, and every tool exposed to the model must convert to an llm-connector tool definition (the new boundary test in main/src/public_mcp_runtime/agent_db_registry_tests.rs is red on the old code).

Screenshot

How to Test

Run the targeted tests (all green locally on this branch):

cargo test -p navop_runtime --lib connections::
cargo test -p agent_runtime --lib tools::spec
cargo test -p main --bin navop agent_runtime_tool_schemas_convert_to_function_calling

Manual check: rebuild the app, then in the built-in AI ask it to save a connection (for example a MySQL connection). The task previously failed immediately with the Invalid schema for function 'connections_save' error; now the tool call is accepted and the connection is created or updated.

Checklist

• I have read the CONTRIBUTING document and followed the guidelines.
• Reviewed the changes in this PR and confirmed AI generated code (If any) is accurate.
• Passed cargo run for story tests related to the changes.
• Tested macOS, Windows and Linux platforms performance (if the change is platform-specific)