feat(mcpserver): let ToolError carry content for is_error results #3032

Job	Run time
checks / pre-commit	43s
checks / readme-snippets	11s
checks / test (3.12, lowest-direct, windows-latest)	1m 28s
checks / test (3.10, locked, ubuntu-latest)	1m 3s
checks / test (3.13, lowest-direct, windows-latest)	1m 53s
checks / test (3.10, lowest-direct, windows-latest)	1m 31s
checks / test (3.14, locked, windows-latest)	2m 9s
checks / test (3.12, locked, ubuntu-latest)	1m 6s
checks / test (3.14, lowest-direct, windows-latest)	1m 26s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 6s
checks / test (3.13, locked, windows-latest)	1m 34s
checks / test (3.13, locked, ubuntu-latest)	58s
checks / test (3.11, locked, ubuntu-latest)	1m 0s
checks / test (3.11, lowest-direct, windows-latest)	1m 29s
checks / test (3.12, lowest-direct, ubuntu-latest)	59s
checks / test (3.12, locked, windows-latest)	1m 34s
checks / test (3.11, locked, windows-latest)	1m 27s
checks / test (3.14, lowest-direct, ubuntu-latest)	58s
checks / test (3.10, locked, windows-latest)	1m 35s
checks / test (3.14, locked, ubuntu-latest)	2m 6s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 6s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 2s
all-green	3s
	28m 27s

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