feat: Add skill for using the checkup CLI

.claude/skills/checkup/SKILL.md

@@ -0,0 +1,107 @@
+---
+name: checkup
+description: Measure data product health with the checkup CLI. Use when the user wants to run checkup, add or configure metrics, check a project's health or governance, or author/edit a checkup.yaml.
+---
+
+# Using the checkup CLI
+
+`checkup` runs **metrics** (from installed checkup plugins like git, dbt, python) against a project and **materializes** the results.
+
+Work in this order: **discover** what's installed → **configure** → **run**. Two ways to configure, pick by longevity:
+
+- **Ad-hoc** — pass everything as `checkup run` flags, no file. Best for a one-off check ("what's the git health of this repo?").
+- **Persistent** — write a `checkup.yaml`. Best when the same metrics run repeatedly, get committed to the repo, or number more than a handful.
+
+## Step 1: Discover what's available
+
+The set of valid metric and provider types depends on which plugins are installed. Never guess them — read them:
+
+```bash
+checkup plugins          # installed plugins + the metrics/providers/materializers each adds
+checkup schema           # writes checkup.schema.json — the authoritative list of valid types and their config keys
+```
+
+`checkup.schema.json` is generated from the *installed* plugins. Read it to see every valid `type`, which config keys each accepts, and which are required. Regenerate it after installing a plugin.
+
+**Completion criterion:** you have the exact type names and config keys for the metrics the user wants, taken from `checkup plugins` / the schema — not invented.
+
+## Step 2: Configure
+
+### Ad-hoc — CLI flags
+
+Pass providers, metrics, and tags directly. With no config file present, these flags *are* the whole config:
+
+```bash
+checkup run -p git -m git_days_since_last_update -m git_tracked_file_count:pattern=src/*
+```
+
+- `-p name[:k=v,...]` provider, `-m type[:k=v,...]` metric, `-t key=value` tag. Repeat each flag per item.
+- Inline config is `type:key=value,key2=value2` (comma-separated).
+- These flags **replace** the corresponding list — combine with `-c` to swap out one list while keeping the file's others.
+
+### Persistent — checkup.yaml
+
+Write the file yourself. Do **not** run `checkup init` or `checkup config` — they are interactive wizards that block waiting for keyboard input you cannot provide.
+
+```yaml
+# yaml-language-server: $schema=checkup.schema.json
+
+tags:                              # free-form key=value, attached to every measurement
+  project: my-data-product
+
+providers:                         # data sources that enrich context
+- name: git
+
+metrics:                           # each entry: type + optional name + inline config keys
+- type: git_days_since_last_update
+- type: git_tracked_file_count
+  pattern: src/*                   # config keys sit inline, as siblings of `type`
+- type: git_tracked_file_count
+  name: tests_exist                # `name` defaults to `type`; set it when a type repeats
+  pattern: tests/*
+
+materializer:                      # optional; defaults to console. One materializer.
+  type: html
+  output_path: report.html
+
+# select / exclude: optional top-level output filters (see Selectors below)
+```
+
+Config keys are inline siblings of `type`/`name`, not nested under a `config:` key. Validate against `checkup.schema.json` before running.
+
+**Completion criterion:** every metric the user asked for is present with a valid `type`, and repeated types have distinct `name`s.
+
+## Step 3: Run
+
+```bash
+checkup run                        # auto-discovers ./checkup.yaml if present; else pass -p/-m flags
+checkup run -c path/to/checkup.yaml
+checkup run --dry-run              # calculate + print to console, materialize nothing (preview / no side effects)
+checkup run -q                     # only materializer output on stdout (machine-readable; status→stderr)
+```
+
+Start with `--dry-run` to confirm metrics compute without errors, then run for real. Errors for individual metrics are reported inline and do not abort the run.
+
+**Completion criterion:** the run reports no unexpected metric errors, and the intended output (console/file) is produced.
+
+## Reference
+
+Run `checkup --help` and `checkup run --help` for the command list and every flag.
+
+- `checkup init` / `checkup config` are **interactive wizards** — they block on keyboard input you can't provide. Author/edit `checkup.yaml` directly instead.
+- `-t` / `-p` / `-m` (tags / providers / metrics) **replace** the config's corresponding list, they don't merge into it.
+- `--no-multiprocessing` runs metrics sequentially — use it when a crashing metric hides the traceback.
+
+### Selectors (`-s`/`--select`, `--exclude`, or `select:`/`exclude:` in config)
+
+Whitespace-separated atoms, each `[method:]pattern`, `*` wildcards. Methods: `name` (default), `tag`, `type`. Selection filters **output only** — every metric is still calculated, so dependencies stay satisfied.
+
+```text
+git_*                              # by name (default method)
+type:git_tracked_file_count        # by metric type
+tag:healthcheck name:python_*      # union of atoms
+```
+
+### Materializer types
+
+`console` (default), `csv`, `html`, `markdown`, `sqlalchemy`. The set depends on installed plugins — `checkup.schema.json` lists what's available and the config keys each accepts.