[dg] removes hidden dg mcp command in preparation for official server

[cmpadden]

Summary & Motivation

Removes the half-baked dg mcp server as our general guidance is to use dagster-io/skills wrapping the dg api.

[greptile-apps]

Greptile Summary

This PR removes the hidden dg mcp command group and its backing FastMCP server, in favour of the external dagster-io/skills approach wrapping the dg api. All implementation files (cli/mcp_server.py, mcp/server.py, mcp/__init__.py), the CLI registration in cli/__init__.py, the test suite, the mcp optional dependency in pyproject.toml, and the dedicated mcp tox environment are cleanly deleted.

• All MCP-related source files and tests are removed with no dangling import references remaining in the package.
• The mcp dependency is correctly dropped from both pyproject.toml ([ai] extras) and tox.ini deps.
• The mcp: tox environment and its --ignore=mcp_tests flag on the general command are both removed.
• Minor leftover: dagster_dg_cli_tests/cli_tests/mcp_tests/__init__.py was not deleted; the empty directory remains in the repo even though the test file was removed.

Confidence Score: 5/5

• Safe to merge — this is a clean deletion of a hidden, half-baked feature with no remaining references in the package.
• All findings are P2 (a leftover empty __init__.py in the test directory). No logic, correctness, or dependency issues remain. The deletion is complete and consistent across source, tests, dependencies, and CI configuration.
• python_modules/libraries/dagster-dg-cli/dagster_dg_cli_tests/cli_tests/mcp_tests/init.py — orphaned empty file after test deletion

Important Files Changed

Filename	Overview
python_modules/libraries/dagster-dg-cli/dagster_dg_cli/cli/init.py	Removes the import and registration of mcp_group from the dg CLI command set — clean two-line removal.
python_modules/libraries/dagster-dg-cli/dagster_dg_cli/cli/mcp_server.py	Deleted entirely — contained the mcp serve and mcp configure CLI subcommands. Clean removal with no dangling references.
python_modules/libraries/dagster-dg-cli/dagster_dg_cli/mcp/server.py	Deleted entirely — contained the FastMCP server with all dg-backed tools. Clean removal.
python_modules/libraries/dagster-dg-cli/dagster_dg_cli_tests/cli_tests/mcp_tests/test_mcp_serve.py	Test file deleted alongside the implementation, but the mcp_tests/__init__.py package marker was not deleted — minor leftover.
python_modules/libraries/dagster-dg-cli/pyproject.toml	Removes mcp from the ai optional-dependency group — consistent with the deleted server code.
python_modules/libraries/dagster-dg-cli/tox.ini	Removes the mcp dep entry and the dedicated mcp: tox environment; also drops the --ignore=mcp_tests flag from the general command now that the test directory is (mostly) gone.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    DG[dg CLI] --> SCAFFOLD[scaffold]
    DG --> DEV[dev]
    DG --> PLUS[plus]
    DG --> LIST[list]
    DG --> UTILS[utils]
    DG --> LAUNCH[launch]
    DG --> CHECK[check]
    DG --> API[api]

    MCP_REMOVED["~~mcp~~ (removed)"]:::removed
    MCP_REMOVED -.->|"serve"| SERVE["~~serve~~"]:::removed
    MCP_REMOVED -.->|"configure"| CONFIGURE["~~configure (claude-desktop / cursor / vscode / claude-code)~~"]:::removed

    classDef removed fill:#fdd,stroke:#f00,color:#900,text-decoration:line-through

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Comments Outside Diff (1)

1. python_modules/libraries/dagster-dg-cli/dagster_dg_cli_tests/cli_tests/mcp_tests/__init__.py, line 1 (link)

   Leftover empty __init__.py after test file deletion

   The test_mcp_serve.py file was deleted, but the containing mcp_tests/__init__.py (and the mcp_tests/ directory itself) was not cleaned up. The tox.ini general command no longer ignores this directory, so pytest will traverse into it — which is harmless since there are no test files, but the orphaned directory and __init__.py are dead weight. Consider deleting the entire dagster_dg_cli_tests/cli_tests/mcp_tests/ directory.

_{Reviews (1): Last reviewed commit: "[dg] removes hidden `dg mcp` command in ..." | Re-trigger Greptile}