Instruction file imported from sbroenne/mcp-server-excel (.github/instructions/architecture-patterns.instructions.md). Copyright stays with the author.

Runtime boundaries

• MCP calls ExcelMcpService in-process; CLI uses the named-pipe daemon. Do not add a daemon hop to MCP or Excel behavior to either adapter.
• Core commands are synchronous. Validate .NET inputs before IExcelBatch.Execute; COM work belongs on its STA callback. Do not wrap it in a catch returning a second result: batch/Service own failure transport and diagnostic context.
• ComInterop owns thread, session, and shutdown lifetime. Follow excel-com-interop.instructions.md for COM changes.
• Public interface parameters use camelCase; generated MCP names use snake_case. Use naming attributes only for exceptions. Unknown action/enum values must fail rather than select a default.
• Never return credentials or unsanitized connection strings, even if an existing code path does so.

Examples and contributor conventions: docs/CONTRIBUTING.md.