Propagate tool failures as ToolExecutionException so MCP clients see isError - #1781
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…isError SpringToolCallbackAdapter.call used to encode every tool failure (Result.Error and thrown exceptions alike) as a plain "ERROR: ..." string. From the MCP client's point of view that looked like a successful call, so isError stayed false even when the tool genuinely failed (#1780). Both failure paths now throw ToolExecutionException instead, always wrapped around a RuntimeException so Spring AI's chat tool loop still converts it into a message for the model rather than rethrowing it. An already-thrown ToolExecutionException passes through unchanged. Signed-off-by: James Dunnam <7660553+jimador@users.noreply.github.com>
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alexheifetz
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July 13, 2026 21:15
alexheifetz
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Jul 13, 2026
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Merging. Streaming Test will be added later.
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Fixes #1780.
SpringToolCallbackAdapter.callswallowed bothTool.Result.Errorand thrown exceptions into"ERROR: ..."string results, so MCP clients received successfultools/callresponses withCallToolResult.isError = falsefor every tool failure — including access-control denials.What changed
ToolExecutionExceptionfor both failure kinds, always with aRuntimeExceptioncause carrying the intended message:Tool.Result.Error(message, cause)→ToolExecutionException(definition, RuntimeException(message, cause))— the error message survives verbatim on the wire.RuntimeException→ passed as the cause directly, preserving the concrete class (e.g.AccessDeniedException) for exception processors configured to rethrow specific types.RuntimeExceptionfirst. This matters:DefaultToolExecutionExceptionProcessorrethrows when the cause is not aRuntimeException, which would break the chat tool loop.Text,WithArtifact) unchanged;SpringToolCallbackWrapper(the reverse adapter) unchanged.Behavior after the change
McpToolUtilshandler catches the exception →isError = truewith the message as content.McpAwareGoalToolalready mapsAccessDeniedExceptiontoTool.Result.Error, so security denials become protocol-level errors with no further change.DefaultToolCallingManagercatches exactlyToolExecutionExceptionand its processor returns the message to the model — same visible behavior as before, minus the"ERROR: "prefix.On the issue's open question (soft vs hard errors): both
Result.Errorand exceptions map to protocol errors — a tool that returnsResult.Errorfailed, and clients branching onisErrorshould see it. No config surface added; easy to revisit if a use case needs split behavior.Testing
SpringToolCallbackAdapterTestupdated from string-prefix assertions toassertThrowswith message assertions.McpToolErrorMappingTestdrives the realMcpToolUtils.toSyncToolSpecificationhandler end to end:isError = truefor runtime,Result.Error, and checked-exception cases (asserting theRuntimeException-cause invariant); happy path stays non-error.embabel-agent-apisuite green (3907 tests, 0 failures).