fix(core): slow the voiceover carve's level release to 2.4s

At 1.6s the bed audibly came back at every sentence break on narrated builds,
which reads as the effect switching off rather than the mix breathing. 2.4s
lets it swell back over a breath. Band-filter release is unchanged; a notch
closing is inaudible. Test timings move with the constant.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

packages/core/src/audioCarve.test.ts

@@ -348,8 +348,9 @@ describe("analyseCarveDuck", () => {
     // of that rather than right against it.
     expect(at(duck, 2)).toBe(0);
     // Back to inaudible by the end of a long tail rather than held down for the
-    // clip; the envelope's last point is pinned at exactly no cut.
-    expect(at(duck, 15)).toBeCloseTo(0, 1);
+    // clip; the envelope's last point is pinned at exactly no cut. Ten seconds
+    // after the last word is four release constants, so the residue has snapped.
+    expect(at(duck, 15.9)).toBeCloseTo(0, 1);
     expect(duck.at(-1)?.v).toBe(0);
   });
 
@@ -383,10 +384,10 @@ describe("analyseCarveDuck", () => {
 
     // Still most of the way down a third of a second after the last word...
     expect(at(duck, 6.3)).toBeLessThan(atSpeech * 0.6);
-    // ...noticeably recovered by a second and a half...
-    expect(at(duck, 7.5)).toBeGreaterThan(atSpeech * 0.5);
-    // ...and within a hair of flat a few seconds later, rather than held down.
-    expect(at(duck, 11)).toBeGreaterThan(-0.6);
+    // ...noticeably recovered two and a half seconds on...
+    expect(at(duck, 8.5)).toBeGreaterThan(atSpeech * 0.5);
+    // ...and within a hair of flat several seconds later, rather than held down.
+    expect(at(duck, 13.5)).toBeGreaterThan(-0.6);
   });
 
   it("finishes the release past the last word instead of snapping at the end", () => {

packages/core/src/audioCarve.ts

@@ -552,13 +552,14 @@ const RELEASE_S = 0.25;
  * jumped to full the instant a word ended, and what you hear then is the effect
  * switching off rather than a mix breathing. Slower than any gap inside a
  * sentence, so it rides through the pauses between words and only recovers
- * between sentences.
+ * between sentences. 1.6s still read as the bed "coming back" at every sentence
+ * break on narrated builds; 2.4s lets it swell back over a breath instead.
  *
  * It also has to be well clear of the envelope's own step. A long voice is
  * measured about every 0.3s, so a release anywhere near that puts the entire
  * recovery inside one step — a jump, whatever the constant claims.
  */
-const DUCK_RELEASE_S = 1.6;
+const DUCK_RELEASE_S = 2.4;
 
 /**
  * Windows an envelope may spend. Held under `MAX_AUTOMATION_POINTS` with room