This lesson is for a developer who has done three commands. You break the map twice and read what check reports. Work in the folder examples/slugline, with unifold set as the alias from README.md.

Delete the line cli.transliteration: unicode.transliteration from unifold.yaml.

Run unifold check. It reports four errors and a warning:

$ unifold check
error G1 docs/diagrams/component.md: generated file is out of date
    fix: Run `unifold generate` (or `unifold check --fix`). A hand-written `AGENTS.md` is not overwritten: move its content to `README.md` and `docs/`, delete it, then run the command.
error G1 docs/diagrams/scenario-slug-from-arguments.md: generated file is out of date
    fix: Run `unifold generate` (or `unifold check --fix`). A hand-written `AGENTS.md` is not overwritten: move its content to `README.md` and `docs/`, delete it, then run the command.
error W2 unifold.yaml:22: need 'cli.transliteration' has no provider
    fix: Add `cli.transliteration: unicode.transliteration` to the wiring.
warn W3 unifold.yaml:22: 'unicode.transliteration' is provided but nothing uses it
    fix: Wire the unit that should use it; where code of the parent itself uses it, declare a need in the parent and wire it (`need: child.capability`); or implement a capability of the parent with it (`capability: child.capability`); or remove the capability.
error N1 unifold.yaml:29: scenario 'slug-from-arguments', hop 'cli -> plugins/unicode.transliterate': no need of 'cli' is provided for by 'plugins/unicode'
    fix: Wire the connection the hop needs, add the part to the contract, or rename what is ambiguous.
4 unit(s): 4 error(s), 1 warning(s), 0 info  [G1×2, N1×1, W2×1, W3×1]

W2 says that the need of cli has no provider. W3 says the same from the other side: nothing uses the capability of unicode. N1 says that the story slug-from-arguments can no longer run: its hop from cli to the plug-in has no connection to run along. G1 says that the component diagram and the diagram of that scenario no longer match the manifests.

Put the line back. Run unifold check. It prints 0 error(s), 0 warning(s) again.
In plugins/unicode/unifold.yaml, change the contract of the need plugin-api to ../../docs/references/slug.md.

Run unifold check. It reports three errors and two warnings:

$ unifold check
error G1 docs/diagrams/scenario-slug-from-arguments.md: generated file is out of date
    fix: Run `unifold generate` (or `unifold check --fix`). A hand-written `AGENTS.md` is not overwritten: move its content to `README.md` and `docs/`, delete it, then run the command.
warn C1 docs/references/slug.md: no `## Parts` section; a contract lists its parts, one `###` heading each
    fix: Write the parts as [writing.md](writing.md#contracts) says.
warn C5 docs/references/slug.md: no `## Fake` section: say what stands in for this contract in the tests of its consumers
    fix: Say what stands in for the contract in the tests of its consumers.
error W11 unifold.yaml:28: need 'unicode.plugin-api' names the contract docs/references/slug.md, capability 'core.plugin-api' names docs/references/plugin-api.md
    fix: Write the definition as a reference of this unit, the one that holds the wiring, or of a unit above it, and point both sides at it with `contract`.
error N1 unifold.yaml:30: scenario 'slug-from-arguments', hop 'plugins/unicode -> core.transliterate': part 'transliterate' is not in the contract docs/references/slug.md
    fix: Wire the connection the hop needs, add the part to the contract, or rename what is ambiguous.
4 unit(s): 3 error(s), 2 warning(s), 0 info  [C1×1, C5×1, G1×1, N1×1, W11×1]

The two sides of one connection now name different documents, so they no longer agree on what travels between them (W11). The document the need names is a reference, not a contract: it has no parts and no fake (C1, C5), so the hop of the scenario finds no part transliterate in it (N1).

Change the contract back to ../../docs/references/plugin-api.md. Run unifold check. It prints 0 error(s), 0 warning(s).

You have seen how check reports a need without a provider, a connection whose sides name different contracts, and a story that can no longer run. It reads no code: a Cargo.toml that uses another crate without a need is for you and your review to notice.