[bborbe]

Adds TaskFrontmatter.Cluster() for the optional cluster frontmatter field (canonical values nukedev, nukeprod, sun; absent or non-string reads as ""). It is documented in the Terminology table of docs/task-flow-and-failure-semantics.md, with Ginkgo tests for absent, string and non-string values. It changes no behaviour; consumers are bborbe/agent-task-executor#82 and the agent-task-controller publish-side filter.

Implemented through dark-factory prompt 238. A follow-up commit reverts three unrelated spec-status flips that the run made.

[ben-s-pull-request-reviewer]

Based on my review of the changes:

Summary: The Cluster() accessor adds a typed getter for the optional cluster frontmatter field, following the established patterns in the file. The implementation correctly handles absent keys and non-string values by returning "", and tests cover both cases. Documentation and CHANGELOG are updated appropriately.

{
  "verdict": "approve",
  "summary": "The Cluster() accessor is a clean addition following existing patterns. Absent-field and non-string cases are handled correctly and tested. CHANGELOG and docs are updated.",
  "comments": [],
  "concerns_addressed": [
    {
      "concern": "correctness: Cluster() accessor must handle absent field, non-string YAML node, and canonical value validation",
      "disposition": "not-an-issue",
      "detail": "Implementation (agent_task-frontmatter.go:62-65) handles absent field and non-string YAML node by returning empty string. Canonical value validation is not performed, consistent with other accessors like Stage() that also skip validation."
    },
    {
      "concern": "correctness: Tests cover absent, string, and non-string cases per PR description — verify edge case coverage",
      "disposition": "not-an-issue",
      "detail": "agent_task-frontmatter_test.go lines 79-94: tests cover absent key (returns \"\"), string value (\"nukedev\"), and non-string value (42 returns \"\")."
    }
  ]
}