refactor(recipe): unify the two topological-sort paths (#1466)

[lockwobr]

Summary

Unify the two topological-sort implementations in pkg/recipe/metadata.go behind one shared graph builder, so TopologicalSort and ComponentRefsTopologicalLevels stop duplicating Kahn's algorithm and its enabled-filtering logic.

Motivation / Context

TopologicalSort (flat DeploymentOrder) and ComponentRefsTopologicalLevels (level-grouped, consumed by the helmfile deployer) each build the dependency graph, apply enabled-filtering, and detect cycles independently. That duplication forced the overrides: {enabled: false} fix in #1465 to be written twice. This extracts the shared work into buildDependencyGraph; the two functions become thin wrappers over it.

Fixes: #1466
Related: #1465

Type of Change

• Refactoring (no functional changes)

Component(s) Affected

• Recipe engine / data (pkg/recipe)

Implementation Notes

• buildDependencyGraph(refs) returns (inDegree, dependents, enabledCount) and centralizes enabled-filtering, edgeSatisfiedExternally, and in-degree/dependents construction.
• Deliberately did NOT derive one function from the other. TopologicalSort uses a globally re-sorted FIFO queue whose flat order can interleave levels alphabetically (e.g. [a, b, z]), which is not the same as flattening the levels ([a, z, b]). Deriving the flat order from the levels would change DeploymentOrder and churn every deployer's output. Both traversals are preserved exactly; only the graph build is shared.
• No behavior change: flat order and level grouping stay byte-identical; the cross-check test TestRecipeMetadataSpecTopologicalLevelsMatchesSort passes unchanged.

Testing

go test -race ./pkg/recipe/...                          # ok
go test -race ./pkg/bundler/deployer/...                # ok (DeploymentOrder consumers unaffected)
golangci-lint run -c .golangci.yaml ./pkg/recipe/...    # 0 issues

All TopologicalSort / TopologicalLevels / MatchesSort subtests pass; every deployer golden is unchanged (ordering preserved).

Risk Assessment

• Low — Pure refactor in a single file, covered by existing tests, trivially reversible.

Rollout notes: N/A. No functional, API, or output change.

Checklist

• Tests pass locally (make test with -race)
• Linter passes (make lint)
• I did not skip/disable tests to make CI green
• I added/updated tests for new functionality
• I updated docs if user-facing behavior changed
• Changes follow existing patterns in the codebase
• Commits are cryptographically signed (git commit -S)

[github-actions]

Recipe evidence check

No leaf overlays affected by this PR.

This gate is warning-only and never blocks merge.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Enterprise

Run ID: aa9dc114-3790-439d-9b54-89ad5ff1e7b0

📥 Commits

Reviewing files that changed from the base of the PR and between 471a57c and a2021b7.

📒 Files selected for processing (1)

• pkg/recipe/metadata.go

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📝 Walkthrough

Walkthrough

Refactored dependency-graph construction in pkg/recipe/metadata.go into the shared buildDependencyGraph helper. The helper filters enabled nodes, handles declared-but-disabled dependencies, preserves undeclared dependency edges, and returns graph metadata plus the enabled-node count. Both ComponentRefsTopologicalLevels and RecipeMetadataSpec.TopologicalSort now use it, with completion checks and result sizing based on enabledCount.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR only shares graph construction; the two Kahn traversal loops remain duplicated, so it doesn't fully unify the topological-sort paths.	Refactor one traversal to derive from the other, or move the full Kahn loop into a shared implementation so both paths become thin wrappers.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the refactor in pkg/recipe.
Description check	✅ Passed	The description matches the change set and explains the shared graph-builder refactor.
Out of Scope Changes check	✅ Passed	All changes stay within pkg/recipe/metadata.go and support the stated refactor.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/unify-topo-sort

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[github-actions]

Coverage Report ✅

Metric	Value
Coverage	78.7%
Threshold	75%
Status	Pass

Coverage Badge

![Coverage](https://img.shields.io/badge/coverage-78.7%25-green)

No Go source files changed in this PR.