ADR-006: A unit test inherits nothing and reaches nothing beyond the machine

Every package under cmd/ and internal/ that has tests seals its process in TestMain with testsupport.SealedMain, which empties every variable mm-mcp reads, listed in config.EnvironmentVariables, and sets MM_MCP_BLOCK_EXTERNAL_NETWORK to 1. While that is set, network.NewSafeTransport, the transport every HTTP client in mm-mcp is built on, refuses any host but localhost, 127.0.0.1 and ::1, and the error names the host it refused. TestEveryTestPackageIsSealed fails a package that has tests and no seal, and TestEveryVariableTheSourceNamesIsListed fails when the code names a variable the list, and so the seal, leaves out.

Build every HTTP client on network.NewSafeTransport. Read configuration through a function that takes a Getenv, as config.FromEnv and cli.Run do, and have a test pass the values it wants with testsupport.Env rather than publish them to the process; t.Setenv is for a test whose subject is the environment, and rules out t.Parallel. Add a variable mm-mcp reads to config.EnvironmentVariables and to the configuration page in the same change.

Unsealed, the machine decides what a test sees: a developer with MM_URL and MM_TOKEN in their shell runs different inputs than a clean runner, and a green run on one is no evidence about the other. An unintended network call makes a suite slow and flaky, fails on an isolated runner, and lets code under test act on a real server with a real token.

Not chosen

• Clear the environment test by test: Every test has to remember to, the one that forgets reads the developer's token, and t.Setenv makes a test sequential.
• Block the network with a mocking library: It covers the clients it is told about, not one added later.