Validate deployment dependency graph before pipeline execution

[temma02]

Description

DependencyGraph is fully implemented and tested in apps/backend/tests/deployment/dependency-graph.test.ts but is never consulted before a deployment pipeline starts. Circular dependencies or missing nodes can cause silent mid-pipeline failures.

Requirements and context

• Must be secure, tested, and documented where applicable
• Should stay reviewable and fit the current monorepo structure
• Relevant files: apps/backend/tests/deployment/dependency-graph.test.ts, apps/backend/src/services/deployment-pipeline.service.ts

Suggested execution

• Create branch: issue-021-validate-deployment-dependency-graph
• Keep changes scoped to the issue and reference the task IDs in the PR

Implement changes

• Build the dependency graph from the deployment's template and customization config at pipeline start
• Call hasCycle() and reject with a descriptive error if a cycle is detected
• Log the topologicalOrder to deployment_logs at info level for observability

Test and commit

• Add pipeline tests for: valid graph proceeds, cyclic graph rejected, missing node rejected
• Verify the deployment status is set to failed with a user-readable message on rejection
• Edge case: single-node graph (no dependencies) must always pass validation

Example commit message

feat(pipeline): validate dependency graph before execution

Guidelines

• Prefer small, reviewable PRs
• Keep naming and data contracts consistent with the spec docs

[Ryjen1]

@Ryjen1 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I will like to get assigned to this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Ryjen1 to this issue.

[drips-wave]

Congratulations, @Ryjen1! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Ryjen1: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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