Grilling: lock MVP Work Graph diagnostic matrix

[cursor]

Part of #300

Blocked by: #301

Question

Lock the MVP diagnostic matrix for Fork–Join Work Graph Spec: which conditions are errors vs warnings vs deferred (cycle, unknown DependsOn, duplicate id, self-dependency, orphan/unreachable, contract mismatch, unregistered-step Analyzer?), and whether Spec filing reserves DP### ids or defers reservation to the first Diagnostics PR.

Respect map #300 Notes; use #301 analogues as input. Do not implement analyzers/generators.

[Skymly]

Resolution — Grilling: lock MVP Work Graph diagnostic matrix

Locked for Spec writing. No analyzer/generator implementation in this ticket.

Hard structural edges (Generator Error)

• Cycle
• Unknown DependsOn target
• Duplicate step id (same graph)
• Self-dependency — separate diagnostic (State DP058-style), not folded only into cycle

Runtime WorkGraphBuilder.Build() should fail with clear exceptions for the same Error set (Spec one-liner; IDs remain generator-side).

Unreachable / “orphan”

• Domain term: unreachable work step (see CONTEXT.md) — registered step not reachable from any zero-indegree root via readiness dependencies.
• Multi-root is valid (e.g. Sample Auth ∥ LoadConfig).
• MVP severity: Warning (not Error / Info; not deferred).

Contract mismatch

• [WorkStep] without valid IWorkStep<TContext> / TContext mismatch vs holder [WorkGraph<T>] → Generator Error.

Unregistered-step Analyzer

• Out of MVP (Phase 2+). Manual builder path does not require attributes.

DP### reservation

• Spec does not allocate IDs.
• First Diagnostics implementation PR assigns from DP087+, syncing DiagnosticIds / descriptors / AnalyzerReleases / AGENTS.md.
• Spec cites the matrix + “IDs at implement time” only.

Analogues used (#301)

• Composite DP011/012, State DP056–059, Step Builder DP082/084; “orphan” overloaded elsewhere (DP059/DP076/Analyzers) — avoided as the Work Graph term.

[Skymly]

Resolved: MVP diagnostic matrix locked; see resolution comment.