46 lines
1.7 KiB
Markdown
46 lines
1.7 KiB
Markdown
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# MCP Versioning and Compatibility (Agent Guide)
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## Why this exists
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Agents can fail for reasons that are already fixed in newer MCP runtime builds. This guide defines where to check runtime/tool versions and where fix records are tracked.
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## Runtime version header
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Whetstone MCP now exposes a `whetstoneVersionHeader` in:
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- `initialize.result`
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- `ping.result`
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- `tools/list.result`
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- `tools/call.result`
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Header fields:
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- `runtimeVersion`: MCP runtime version (for example `0.8.4`)
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- `protocolVersion`: MCP protocol date string
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- `toolContractDefaultVersion`: default contract version for tools
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- `toolSurfaceSchemaVersion`: schema snapshot version
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- `toolCount`: tool count in the running server
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- `toolSurfaceFingerprint`: deterministic fingerprint of tool names
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- `compatibilityLedger.path`: path to the issue/fix ledger JSON
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- `compatibilityLedger.version`: ledger schema/snapshot version
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## Tool-level contract header
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Each `tools/list` entry includes `x-whetstone`:
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- `contractVersion`
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- `compatibilityLedger`
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## Compatibility ledger
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Machine-readable ledger:
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- `docs/mcp_compatibility_ledger.json`
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Use this for checks like:
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- "Issue reproduced on `runtimeVersion=0.8.1`"
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- "Ledger says fixed in `0.8.4`"
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- "Action: update server runtime before more debugging"
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## Recommended triage flow for agents
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1. Call `initialize` (or `ping`) and capture `whetstoneVersionHeader`.
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2. If behavior seems wrong, read `docs/mcp_compatibility_ledger.json` and match symptom tags.
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3. If `runtimeVersion < fixed_in`, report upgrade recommendation first.
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4. Only escalate to deep debugging after version mismatch is ruled out.
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## Notes
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- Keep ledger entries small and concrete (symptom, affected tools, fixed version).
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- Add entries when a recurring failure pattern is fixed deterministically.
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