fix(python/mcp): gate tool output on settlement success#2356
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phdargen merged 2 commits intoMay 18, 2026
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The MCP payment wrappers in server_sync.py and server_async.py called
facilitator.settle() but never branched on settle_result.success before
returning the wrapped tool's output. A signed EIP-3009 authorization
could be replayed indefinitely: verify passed each time, the tool ran,
settle returned success=False with AuthorizationAlreadyUsed, and the
wrapper returned the tool output stamped with the failed settlement
response in _meta.
Mirror the success check from the non-MCP path in server.py and route
to the existing _create_settlement_failed_result_{sync,async} helpers
on failure. Add regression tests covering the success=False branch
(distinct from the existing exception-path test) and assert that
on_after_settlement does not fire on failure.
Also fix a stale signature on the test mock's
_create_payment_required_response_real that was missing the extensions
parameter, which had been masking other test failures.
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…ettlement-success-check
phdargen
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May 18, 2026
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Looks great, thank you @apmcdermott
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Description
The MCP payment wrappers in
python/x402/mcp/server_sync.pyandserver_async.pycallfacilitator.settle()but don't branch onsettle_result.successbefore returning the wrapped tool's output. Add the missing check so a failed settlement returns a structured 402 error result, matching the HTTP server path atpython/x402/server.py:225-243.Tests
python/x402/mcp/tests/test_server.py::test_create_payment_wrapper_settlement_returns_failurepython/x402/mcp/tests/test_server_async.py::test_create_payment_wrapper_async_settlement_returns_failurepython/x402/tests/unit/mcp/test_server_wrappers.py— verifies the settlement-failure helpers preserve extensionsChecklist