[BUG] computer-use MCP: tool invocation failures silently swallowed — agent continues as if operation succeeded

Description

When Claude Code calls computer-use MCP tools (e.g. mcp_cua_driver_*) with invalid or incorrect parameters, the invocation silently fails and the error is not surfaced to the model. The agent then continues generating output (code, plans, designs) based on the false assumption that the tool call succeeded.

Example

A typical failing call pattern:

call
<invoke name="mcp__cua__computer">
<parameter name="action">get_screenshot</parameter>
</invoke>

Problems:

1. Wrong tool name: mcp__cua__computer (double underscore + "computer" vs correct driver names like mcp_cua_driver_get_window_state).
2. Wrong parameters: action="get_screenshot" is not a valid parameter for any CUA driver tool.

Expected: The error should be surfaced to the model as a tool-call failure, and the model should retry or adapt.

Actual: The call fails silently (the "Crunched for Xm Ys" message appears at the end with no error detail), and the model continues reasoning as if the screenshot was successfully obtained. In practice it goes on to write code, propose designs, or make assertions based on nonexistent data.

Impact

• Invalid probe results feed into design decisions (e.g., proposing AX element coordinates without having actually verified them).
• The agent writes code based on assumptions that were never validated.
• For macOS automation workflows targeting Electron apps (e.g. 剪映专业版/VideoFusion), this is especially problematic because the AX tree of these apps is complex and errors are common — but they must be surfaced to be actionable.

Expected behavior

When a computer-use MCP tool-call encounters an error (invalid parameters, tool not found, connection issue, permission denied), the error should be:

1. Returned in the tool response so the model can see and handle it.
2. Displayed in the terminal output (not hidden behind a generic "Crunched for..." message).

Environment

• Claude Code version: latest
• Platform: macOS
• MCP tools: cua-driver-rs (computer-use macOS tools)