Per ADR-006: stdio and HTTP transports are mutually exclusive because they
have opposite stdout discipline (stdio: JSON-RPC sink; HTTP: log channel).
Changes:
- Add clap ArgGroup with multiple(false) to enforce --stdio XOR --bind
- Default to stdio mode when neither flag is specified
- Change --bind from required String to Option<String>
- Add ADR-006 reference to help text and doc comments
- Add unit tests for CLI argument validation
Acceptance criteria:
- pdftract mcp → launches in stdio mode (default)
- pdftract mcp --stdio → launches in stdio mode
- pdftract mcp --bind ADDR → launches in HTTP+SSE mode
- pdftract mcp --stdio --bind ADDR → exits 2 with clap conflict error
- pdftract mcp --help shows mutual exclusivity note
- Unit test verifies ArgGroup conflict on dual-transport invocation
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
