**Focus:** Validate the per-unit knowledge artifact for game concept. Units here define what the game IS (pillars, core loop, fantasy, audience, scope) — knowledge artifacts that downstream prototype/production stages consume. Validation checks substance, internal coherence, and decision-register accountability. NOT executable verify-commands or DAG validity.

**Anti-patterns (RFC 2119):**
- The agent **MUST NOT** read or interpret unit frontmatter. workflow engine territory.
- The agent **MUST NOT** validate against execution-spec rules.
- The agent **MUST NOT** advance a unit with placeholders, content-free outlines, or empty sections.
- The agent **MUST NOT** soften scope ("we'll figure out platforms later"). Scope is concrete here or rejected.
- The agent **MUST** name a specific failed criterion in any rejection.

## What you check (BODY ONLY)

### 1. Artifact answers its topic
The body MUST deliver substantive content on the unit's topic. Pillars: 3-5 short declarative statements with rationale. Core loop: minute-to-minute actions with what each produces. Fantasy: first-person sentence + delivering experiences. Etc.

### 2. Concrete, not adjectival
Game concept is rife with vague-sounding-concrete drift. Reject "engaging gameplay", "satisfying loop", "fun mechanics" without specifics. Acceptable: "five-second engagement loop where the player makes one resource decision and sees its consequence visualized within the same loop."

### 3. Internal consistency (CRITICAL for concept)
- Pillars MUST be reflected in the Core Loop (a "co-op trust" pillar with a solo-only loop is a contradiction).
- Fantasy MUST be deliverable by the Core Loop (a "power fantasy" with a passive watching loop is a contradiction).
- Audience MUST be plausible buyers of the Fantasy + Loop combination.
- Scope MUST be feasible for the team/budget context — flag obvious mismatches (100-hour open world on $50K budget).

### 4. Decision-register consistency
The unit must not propose pillars/loop/scope contradicting recorded Decisions (e.g., concept says "single-player only" when Decision N chose "co-op as a launch feature"). Cite the Decision ID.

### 5. Open questions accounted for
Every "Open Questions" entry must be answered, defaulted, OR flagged `(needs human escalation)`.
