feat: add Nika workflow language rule (.nika.yaml authoring)

[ThibautMelen]

Adds a rule for the Nika workflow language (.nika.yaml files — AI workflows as reviewable DAGs).

The rule teaches Cursor the envelope, the four verbs, the interpolation/binding forms, and the authoring discipline (run nika check after every edit, repair from diagnostics). Scoped by globs to **/*.nika.yaml only, alwaysApply: false.

Provenance note: this is exactly the rule the nika init command generates (engine v0.99.0) — contributed here so Cursor users get it without installing anything first. I'll refresh it if the language surface ever changes (the envelope and verbs are frozen).

Disclosure: I'm the author of Nika (AGPL-3.0 Rust engine).

Summary by CodeRabbit

• Documentation
  • Added authoring guidance for Nika workflow files.
  • Documented supported workflow verbs, syntax conventions, bindings, model naming format, and dependency declarations.
  • Added secret handling rules (including prohibited inline literal secret keys) and required reference format.
  • Included validation and troubleshooting guidance using the appropriate Nika commands.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 84373a7c-10e9-4aff-bfb3-b362419b9c5b

📥 Commits

Reviewing files that changed from the base of the PR and between 439a218 and 311c522.

📒 Files selected for processing (1)

• rules/nika-workflow-language.mdc

✅ Files skipped from review due to trivial changes (1)

• rules/nika-workflow-language.mdc

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📝 Walkthrough

Walkthrough

Adds a Nika workflow language rules document covering file targeting, the nika: v1 envelope, supported verbs, authoring constraints, secret sourcing, validation, and troubleshooting.

Changes

Nika workflow rules

Layer / File(s)	Summary
Define Nika workflow authoring rules rules/nika-workflow-language.mdc	Documents target file globs, the immutable nika: v1 envelope, supported verbs, interpolation and binding patterns, model naming, depends_on structure, secret handling, nika check, and nika explain NIKA-XXXX.

Estimated code review effort: 1 (Trivial) | ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the new Nika workflow language rule and matches the change set.
Description check	✅ Passed	The description covers the summary, value, file scope, and provenance, but it does not use the repository's template sections verbatim.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 3

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@rules/nika-workflow-language.mdc`:
- Line 3: Restrict the frontmatter glob to the PR’s stated target by removing
the **/*.nika.yml pattern, keeping only **/*.nika.yaml so it matches the
contract described in the rule.
- Around line 18-22: The workflow language guidance incorrectly directs secrets
through the env namespace. Update the rule in the interpolation and secrets
guidance to document `${{ secrets.KEY }}` for credentials, distinguish it from
non-sensitive `${{ env.KEY }}` configuration, and retain the prohibition on
inline literal keys.
- Line 12: Update the documented `infer` signature in the workflow language rule
to include the optional `max_tokens` parameter alongside `prompt`, `system?`,
`temperature?`, and `schema?`, matching the supported examples.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 2b799d9e-0d70-41ac-9a48-ba95eeda24b7

📥 Commits

Reviewing files that changed from the base of the PR and between b044f95 and 439a218.

📒 Files selected for processing (1)

• rules/nika-workflow-language.mdc

[coderabbitai]

🎯 Functional Correctness | 🟠 Major | ⚡ Quick win

Restrict the glob to the PR’s stated target.

The rule currently also applies to **/*.nika.yml, while the objective and line 9 specify .nika.yaml files only. Remove the .nika.yml pattern or update the contract consistently.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@rules/nika-workflow-language.mdc` at line 3, Restrict the frontmatter glob to
the PR’s stated target by removing the **/*.nika.yml pattern, keeping only
**/*.nika.yaml so it matches the contract described in the rule.

[ThibautMelen]

All three findings verified against the shipped binary (v0.99.0) and fixed:

1. max_tokens — real gap: the engine's schema lists max_tokens (and model) on infer; added to the signature line.
2. secrets — real: the actual form is a declared secrets: block referenced as ${{ secrets.name }}; the line now says exactly that and scopes env.* to non-sensitive config.
3. globs — the engine intentionally matches both .nika.yaml and .nika.yml (the globs come from nika init itself); the prose now names both instead of dropping the pattern.

Also filed upstream so the generator emits the same fixes (the rule stays in sync with the binary).