fix: keep mindmodel constraint files on the .md extension (#58)

[vtemian]

Closes #58.

Problem

/mindmodel generated constraint files ending in .yaml instead of .md. Reported against qwen3.6 35b.

The generator prompt was not actually wrong, which is why this is easy to miss: its <output-structure> block lists every constraint file with a .md extension and only manifest.yaml as YAML. But the rule was only ever implied by that listing. Sitting right beside it is a <manifest-format> block containing a yaml code fence, and a weaker model reads that as licence to write the whole directory as YAML.

Fix

Two parts, because prompt wording alone is not verifiable.

Say the rule outright. <rules> now states that manifest.yaml is the only YAML file and names the exact mistake, rather than leaving it to be inferred from a directory diagram.

Report it when it happens anyway. The loader now names any category path that is not .md:

[mindmodel] Constraint files must end in .md: stack/frontend.yaml, patterns/logging.yml

Deliberately a warning, not a parse failure. A wrong extension leaves the directory inconsistent rather than broken, since the file still loads by its declared path. Failing the manifest would discard an otherwise usable mindmodel over a naming problem, and the project's own guidance is to treat parse issues as non-fatal where possible.

Verification

490 tests pass (was 488). Two new cases: one asserting the warning names only the offending paths while the manifest still loads with all three categories intact, one asserting silence when every path is .md.

Mutation-checked: removing the warnNonMarkdownCategories call fails the first test.

The prompt change itself is not testable here, since it depends on model behaviour. The loader warning is what makes a bad generation visible rather than silent.

[cursor]

Bugbot is not enabled for your account, so this pull request was not reviewed.

Enable Bugbot in the Cursor dashboard to get automatic reviews on future PRs.

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}