Concept machinery: survive truncation, builds, and loud briefs

The release-gate audit traced four ways the roll's output was defeated
downstream of a perfectly healthy seed. Gemini's harness keeps only the
tail of tool output, so the header-only ASSIGNED INDEX never reached
the model in 18 of 18 samples; the seed now restates the assignment
and key at the end of its output. Astro strips frontmatter comments,
so half the anthropic contracts vanished from built artifacts; the
contract now must survive the production build as an HTML comment in
emitted markup. A brief that paints its own picture (the album named
Soft Cathedrals) converged every arm regardless of assigned index; its
literal reading now joins the rut with at most one candidate. And Opus
under 4.0.1 skipped the seed 42% of the time while hand-authoring
plausible contracts; the finish reviewer now verifies FORM carries a
corroborable seed key before any craft point.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

skill/scripts/concept-seed.mjs

@@ -470,6 +470,8 @@ channel: when a browser can open, present the direction on the decision page
 the no-browser fallback.
 ${authorityInstruction}
 A user- or brief-pinned decision beats the roll, always.
+ASSIGNED INDEX (restated for truncated readers): ${buildIndex}. Build candidate
+${buildIndex} of your own grounded list; seed key ${key}.
 `;
   }
 
@@ -510,6 +512,8 @@ never as a mockup to copy; your surface serves this product, not that render.
 ${authorityInstruction}
 ${richnessInstruction}
 ${telemetryBlock}A user- or brief-pinned decision beats the roll, always.
+ASSIGNED INDEX (restated for truncated readers): ${buildIndex}. Build candidate
+${buildIndex} of your own grounded list; seed key ${key}.
 `;
 }