Frontend: site chrome, demo shell, pages, and the contract gates

Five parallel lanes plus an integration pass. The header, gallery, router and
sitemap are all generated from the demo registry, so adding src/demos/<slug>/
puts a demo everywhere with zero edits to shared files — which is the whole
reason demo nine cannot break demo one.

check-demos enforces the twelve contract rules: 142 checks over one live demo.
Two worth naming. The shell may not mention a specific slug, because an
'if (slug === wordle)' in src/components/demo/ is a contract bug wearing a
patch. And a spec-status demo must ship a real specification — task, actions,
grader, counterweight, eval command — since a coming-soon card reads worse than
an honest empty gallery.

Bundle budget holds: entry 108.79 kB gzipped against a 160 kB ceiling, the demo
chunk 21.15 kB against 90 kB. recharts is 108 kB gzipped and lives behind a lazy
import so it never touches the entry.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019mt6sHQHEnEYrJZvoMCJSB

src/demos/_template/reward.py

@@ -0,0 +1,53 @@
+"""The reward this demo quotes, as a runnable placeholder.
+
+A real demo points `reward.source.path` at its environment package — e.g.
+`envs/__package__/__package__/reward.py` — and quotes the function the grader
+actually runs. This file exists so a freshly scaffolded demo has a receipt that
+RESOLVES on day one: an empty receipt panel reads to a visitor as the code not
+existing, which is the exact impression this site is built to avoid.
+
+Move the region markers into the environment and repoint `source.path` as soon
+as the environment lands. `scripts/check-receipts.mjs` will tell you the moment
+the two disagree.
+"""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Episode:
+    """One rollout, as the environment records it."""
+
+    escalated: frozenset[str]
+    needed: frozenset[str]
+    malformed_actions: int
+
+
+# region: pig-demo/score
+def score(episode: Episode) -> dict[str, float]:
+    """Three terms, weighted 0.60 / 0.25 / 0.15 in the demo's RewardSpec.
+
+    `caught` is the objective. `restraint` is the counterweight: it is what
+    stops the objective being maximised the crude way, by escalating the whole
+    queue. `well_formed` is a gate — every competent policy scores 1.0 on it,
+    so it is declared a gate rather than dressed up as a second counterweight.
+    """
+    needed = episode.needed
+    escalated = episode.escalated
+
+    caught = len(escalated & needed) / len(needed) if needed else 1.0
+
+    noise = escalated - needed
+    quiet = len(escalated) - len(noise)
+    restraint = 1.0 - (len(noise) / len(escalated)) if escalated else 1.0
+
+    well_formed = 0.0 if episode.malformed_actions else 1.0
+
+    return {
+        "caught": caught,
+        "restraint": restraint,
+        "well_formed": well_formed,
+        # Unweighted diagnostic. Rendered, never summed into the reward.
+        "escalations_that_landed": float(quiet),
+    }
+# endregion: pig-demo/score