fix(mcp): warn and return empty when native MCP server returns no tools

[greysonlalonde]

Closes #5116

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Note

Low Risk
Low risk: adds a guard for an empty discovered-tools list and corresponding tests; behavior only changes for the edge case where discovery yields no tools or filtering removes them all.

Overview
Native MCP tool discovery now logs a warning and returns empty results when list_tools() returns no tools (including when a tool_filter removes everything), instead of continuing into tool construction.

Adds native-path tests covering the empty-tools behavior and ensuring unexpected RuntimeErrors still bubble up as Failed to get native MCP tools.

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[iris-clawd]

LGTM — bare raise fix prevents silent swallowing of unmatched RuntimeErrors, empty tools guard is clean. Good tests.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Misleading warning message after tool filtering removes all tools

Low Severity

The if not tools_list: check is placed after the tool_filter logic, so when the filter removes all tools, the warning message says "No tools discovered from MCP server: {server_name}" — implying the server returned nothing. This is misleading when tools were returned by the server but were all excluded by the user's tool_filter. Users debugging this scenario would investigate their MCP server configuration instead of their filter logic.

 

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