[ehz0ah]

Description

VikingBot previously reduced every exception from an outbound MCP tools/call request to the exception class name. When a reachable server returned a JSON-RPC error for invalid arguments, the model saw only McpError and lost the information needed to correct the call.

JSON-RPC error answers now produce a bounded, credential-redacted result that includes the error code and server message. The MCP SDK's connection-closed and request-timeout codes remain on the existing transport-failure path.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

External evidence: NousResearch/hermes-agent#142864

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Recognize JSON-RPC error answers structurally without depending on one MCP SDK exception class.
• Return the server's code and sanitized message to the model for actionable call rejection errors.
• Preserve the existing generic result for no-answer codes, malformed error objects, and ordinary exceptions.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Validation completed:

ruff format --check bot/vikingbot/agent/tools/mcp.py bot/tests/test_mcp_tool_errors.py
ruff check bot/vikingbot/agent/tools/mcp.py bot/tests/test_mcp_tool_errors.py
python3 -m py_compile bot/vikingbot/agent/tools/mcp.py bot/tests/test_mcp_tool_errors.py
git diff --check

A source-pinned before/after probe ran twice per revision with byte-identical output. It verified that -32603 becomes actionable, -32000 and -32001 remain generic transport failures, malformed and ordinary exceptions retain their current result, and credential-shaped message content is redacted.

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Not applicable.

Additional Notes

This change does not add retries, replay failed calls, open a circuit breaker, or alter MCP connection ownership.