feat(sim+engine): lock alteration calibration + fix psychedelic dark grade

Tuning the look by eye in the simulator (design §8) surfaced that the dark
mood pole rendered a full-frame hue-rotate(-200deg) — rock orange, trees
purple: the disorienting look rejected in session 0008, not the peaceful POC
dark_frame. Replace it with darken + slight desaturate on the video filter
plus a multiply-blended deep-blue wash (#tint, below the SVG HUD so the
overlay stays legible). Dark now reads cool/somber with natural greens, like
the approved POC look; light/left/right unchanged and confirmed peaceful.

With full tilt now tasteful on every axis, LOCK DEFAULT_CALIBRATION to unity
gains + linear variant map as a deliberate by-eye choice (not placeholders),
closing the open session-0006 knob->strength decision: knobs run 0=off..4=max,
equal Dark/Light = identity, the 5 notches map 1:1 to the 5 discrete Right
bakes. Guard the locked constants with test_default_calibration_is_locked.

Resolves design §8 open questions (calibration curve shape; grade-vs-overlay
ordering) and records the dark-grade fix. Full suite 193 passed / 2 skipped.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

simulator/static/app.js

@@ -1,7 +1,7 @@
 // Thin renderer: post controls+calibration -> RenderPlan; render grade, Right
 // variant crossfade, and the live Left overlay. All math stays in Python.
 const $ = (id) => document.getElementById(id);
-const vid = $("vid"), overlay = $("overlay"), black = $("black"), readout = $("readout");
+const vid = $("vid"), tint = $("tint"), overlay = $("overlay"), black = $("black"), readout = $("readout");
 
 let clip = null;           // active clip manifest entry
 let currentVariant = -1;   // last loaded Right strength
@@ -19,12 +19,16 @@ function variantFile(strength) {
 }
 
 function applyGrade(tone) {
-  // Light: warm + brighten; Dark: cool + darken; 0: raw.
+  // Light: warm + brighten (sepia). Dark: cool + darken via a multiply-blended
+  // blue wash (#tint) that lifts shadows toward blue while keeping natural
+  // greens — the peaceful POC dark look, NOT a full-frame hue spin.
   const warm = tone > 0 ? tone : 0, cool = tone < 0 ? -tone : 0;
-  const bright = 1 + 0.25 * tone, sat = 1 + 0.15 * Math.abs(tone);
+  const bright = 1 + 0.25 * warm - 0.35 * cool;
+  const sat = 1 + 0.15 * warm - 0.30 * cool;
   vid.style.filter =
-    `brightness(${bright}) saturate(${sat}) ` +
-    `sepia(${(warm * 0.5).toFixed(3)}) hue-rotate(${(-cool * 200).toFixed(0)}deg)`;
+    `brightness(${bright.toFixed(3)}) saturate(${sat.toFixed(3)}) ` +
+    `sepia(${(warm * 0.5).toFixed(3)})`;
+  tint.style.opacity = (cool * 0.6).toFixed(3);
 }
 
 function loadVariant(strength) {

simulator/static/index.html

@@ -12,6 +12,7 @@
     <section class="stage">
       <div class="screen">
         <video id="vid" loop muted playsinline></video>
+        <div id="tint"></div>
         <svg id="overlay" viewBox="0 0 100 100" preserveAspectRatio="none"></svg>
         <div id="black" class="black hidden"></div>
       </div>

simulator/static/style.css

@@ -7,6 +7,9 @@ main { display: flex; gap: 1rem; padding: 1rem; flex-wrap: wrap; }
 .screen { position: relative; width: 100%; aspect-ratio: 16 / 9; background: #000;
           border-radius: 6px; overflow: hidden; }
 #vid { width: 100%; height: 100%; object-fit: cover; transition: opacity 0.15s ease; }
+#tint { position: absolute; inset: 0; pointer-events: none; opacity: 0;
+        background: #28425f; mix-blend-mode: multiply;
+        transition: opacity 0.2s ease; }
 #overlay { position: absolute; inset: 0; width: 100%; height: 100%;
            pointer-events: none; transition: opacity 0.2s ease; }
 .anno-box { fill: none; stroke: #6cf; stroke-width: 0.4; vector-effect: non-scaling-stroke; }