diff --git a/.fallowrc.jsonc b/.fallowrc.jsonc
index 3a29f215b..de8373d2e 100644
--- a/.fallowrc.jsonc
+++ b/.fallowrc.jsonc
@@ -149,13 +149,6 @@
       "file": "packages/studio/src/utils/studioHelpers.ts",
       "exports": ["resolveDroppedAssetDimensions"],
     },
-    // Audio FX worklets sit near the bottom of the audio stack: the worklet
-    // source and its test reset are consumed by the runtime and engine PRs
-    // upstack, so a per-PR audit against the merge base sees them as unused.
-    {
-      "file": "packages/core/src/audio/audioFxWorklets.ts",
-      "exports": ["AUDIO_FX_WORKLET_SOURCE", "__resetAudioFxWorkletsForTests"],
-    },
     {
       "file": "packages/core/src/audio/audioFxGraph.ts",
       "exports": ["ensureAudioFxWorklets"],
diff --git a/packages/core/src/audio/audioFxGraph.test.ts b/packages/core/src/audio/audioFxGraph.test.ts
index 1a8d23519..316deff7a 100644
--- a/packages/core/src/audio/audioFxGraph.test.ts
+++ b/packages/core/src/audio/audioFxGraph.test.ts
@@ -155,6 +155,16 @@ describe("buildFxNode", () => {
     expect(workletNodes[0]!.messages[0]).toMatchObject({ threshold: -30 });
   });
 
+  it("tells a worklet processor to retire on dispose, not just disconnect it", () => {
+    // Disconnecting leaves the processor alive — it lives until `process()`
+    // returns false — so every rebuild that dropped a worklet effect left one
+    // running on the audio thread for the rest of the session.
+    workletNodes.length = 0;
+    const h = buildFxNode(asCtx(ctx()), "compressor", defaultAudioFxParams("compressor"));
+    h.dispose();
+    expect(workletNodes[0]!.messages).toEqual([{ __hfDispose: true }]);
+  });
+
   it("rebuilds the saturation curve for the selected shape", () => {
     const c = ctx();
     buildFxNode(asCtx(c), "saturate", { ...defaultAudioFxParams("saturate"), type: "hard" });
diff --git a/packages/core/src/audio/audioFxGraph.ts b/packages/core/src/audio/audioFxGraph.ts
index f4bc818dd..f7c7130cb 100644
--- a/packages/core/src/audio/audioFxGraph.ts
+++ b/packages/core/src/audio/audioFxGraph.ts
@@ -182,7 +182,17 @@ function workletBuilder(processor: string): Builder {
       input: node,
       output: node,
       update: (v) => node.port.postMessage({ ...v }),
-      dispose: () => node.disconnect(),
+      dispose: () => {
+        // Disconnecting is not enough to retire an AudioWorkletProcessor: it
+        // lives until its `process()` returns false, and these all returned
+        // true unconditionally. So every chain rebuild that dropped a limiter,
+        // compressor, gate or bitcrush left it running on the audio thread for
+        // the rest of the session, and a few edits to a carved bed accumulated
+        // a stack of them. The processors treat this message as their cue to
+        // stop.
+        node.port.postMessage({ __hfDispose: true });
+        node.disconnect();
+      },
     };
   };
 }
diff --git a/packages/core/src/audio/audioFxWorklets.test.ts b/packages/core/src/audio/audioFxWorklets.test.ts
new file mode 100644
index 000000000..1e9e06ca6
--- /dev/null
+++ b/packages/core/src/audio/audioFxWorklets.test.ts
@@ -0,0 +1,103 @@
+import { describe, expect, it, vi } from "vitest";
+import { audioFxWorkletsReady, ensureAudioFxWorklets } from "./audioFxWorklets.js";
+
+/** Just enough of a BaseAudioContext for the registration cache to key on. */
+const contextWith = (addModule: (url: string) => Promise<void>): BaseAudioContext =>
+  ({ audioWorklet: { addModule } }) as unknown as BaseAudioContext;
+
+describe("ensureAudioFxWorklets", () => {
+  it("registers once per context and reuses the result", async () => {
+    const addModule = vi.fn(async () => undefined);
+    const ctx = contextWith(addModule);
+
+    await ensureAudioFxWorklets(ctx);
+    await ensureAudioFxWorklets(ctx);
+
+    expect(addModule).toHaveBeenCalledTimes(1);
+    expect(audioFxWorkletsReady(ctx)).toBe(true);
+  });
+
+  it("retries after a failure instead of replaying it forever", async () => {
+    // The rejected promise used to stay in the cache, so every later attempt
+    // got the same rejection back — the limiter, compressor, gate and bitcrush
+    // were silent for the life of the context after one transient failure.
+    const addModule = vi
+      .fn<(url: string) => Promise<void>>()
+      .mockRejectedValueOnce(new Error("module load failed"))
+      .mockResolvedValue(undefined);
+    const ctx = contextWith(addModule);
+
+    await expect(ensureAudioFxWorklets(ctx)).rejects.toThrow("module load failed");
+    expect(audioFxWorkletsReady(ctx)).toBe(false);
+
+    await expect(ensureAudioFxWorklets(ctx)).resolves.toBeUndefined();
+    expect(addModule).toHaveBeenCalledTimes(2);
+    expect(audioFxWorkletsReady(ctx)).toBe(true);
+  });
+
+  it("refuses a context with no AudioWorklet rather than hanging", async () => {
+    const ctx = {} as BaseAudioContext;
+    await expect(ensureAudioFxWorklets(ctx)).rejects.toThrow(/secure context/);
+  });
+});
+
+/**
+ * A processor lives until its `process()` returns false — disconnecting the
+ * node does not retire it. These all returned true unconditionally, so every
+ * chain rebuild that dropped a worklet effect left it running on the audio
+ * thread for the rest of the session.
+ *
+ * The source is taken from the data: URL registration actually hands to
+ * `addModule`, so this also proves the URL carries what it claims to.
+ */
+describe("the worklet processors themselves", () => {
+  /** Evaluate the registered module and hand back the processor classes by name. */
+  async function loadProcessors(): Promise<Map<string, new (o: unknown) => Processor>> {
+    let moduleSource = "";
+    await ensureAudioFxWorklets(
+      contextWith(async (url: string) => {
+        moduleSource = atob(url.replace("data:text/javascript;base64,", ""));
+      }),
+    );
+    const made = new Map<string, new (o: unknown) => Processor>();
+    class Base {
+      port = {
+        onmessage: null as ((e: { data: unknown }) => void) | null,
+        postMessage: (data: unknown) => this.port.onmessage?.({ data }),
+      };
+    }
+    new Function("AudioWorkletProcessor", "registerProcessor", "sampleRate", moduleSource)(
+      Base,
+      (name: string, cls: new (o: unknown) => Processor) => made.set(name, cls),
+      48000,
+    );
+    return made;
+  }
+
+  interface Processor {
+    port: { postMessage(data: unknown): void };
+    process(inputs: Float32Array[][], outputs: Float32Array[][]): boolean;
+  }
+
+  const block = (): Float32Array[][] => [[new Float32Array(128)]];
+
+  it("every processor keeps running until it is told to stop, then retires", async () => {
+    const processors = await loadProcessors();
+    expect([...processors.keys()]).toEqual([
+      "hf-compressor",
+      "hf-limiter",
+      "hf-gate",
+      "hf-bitcrush",
+    ]);
+
+    for (const [name, Cls] of processors) {
+      const p = new Cls({ processorOptions: {} });
+      expect(p.process(block(), block()), `${name} retired before it was disposed`).toBe(true);
+      p.port.postMessage({ __hfDispose: true });
+      expect(p.process(block(), block()), `${name} kept running after dispose`).toBe(false);
+      // And it stays retired — a later parameter update must not revive it.
+      p.port.postMessage({ mix: 0.5 });
+      expect(p.process(block(), block()), `${name} came back to life`).toBe(false);
+    }
+  });
+});
diff --git a/packages/core/src/audio/audioFxWorklets.ts b/packages/core/src/audio/audioFxWorklets.ts
index e421d3409..f2261ea8a 100644
--- a/packages/core/src/audio/audioFxWorklets.ts
+++ b/packages/core/src/audio/audioFxWorklets.ts
@@ -60,11 +60,13 @@ class HfCompressor extends AudioWorkletProcessor {
     this.p = o.processorOptions || {};
     this.env = new EnvBank(this.p.attack ?? 20, this.p.release ?? 250);
     this.port.onmessage = (e) => {
+      if (e.data && e.data.__hfDispose) { this.dead = true; return; }
       this.p = { ...this.p, ...e.data };
       this.env.set(this.p.attack ?? 20, this.p.release ?? 250);
     };
   }
   process(inputs, outputs) {
+    if (this.dead) return false;
     const i = inputs[0], o = outputs[0];
     if (!i || !i.length) return true;
     const p = this.p;
@@ -105,11 +107,13 @@ class HfLimiter extends AudioWorkletProcessor {
     this.p = o.processorOptions || {};
     this.env = new EnvBank(this.p.attack ?? 5, this.p.release ?? 50);
     this.port.onmessage = (e) => {
+      if (e.data && e.data.__hfDispose) { this.dead = true; return; }
       this.p = { ...this.p, ...e.data };
       this.env.set(this.p.attack ?? 5, this.p.release ?? 50);
     };
   }
   process(inputs, outputs) {
+    if (this.dead) return false;
     const i = inputs[0], o = outputs[0];
     if (!i || !i.length) return true;
     const ceiling = dbToLin(this.p.limit ?? -1);
@@ -136,11 +140,13 @@ class HfGate extends AudioWorkletProcessor {
     this.env = new EnvBank(this.p.attack ?? 1, this.p.release ?? 100);
     this.gains = [];
     this.port.onmessage = (e) => {
+      if (e.data && e.data.__hfDispose) { this.dead = true; return; }
       this.p = { ...this.p, ...e.data };
       this.env.set(this.p.attack ?? 1, this.p.release ?? 100);
     };
   }
   process(inputs, outputs) {
+    if (this.dead) return false;
     const i = inputs[0], o = outputs[0];
     if (!i || !i.length) return true;
     const p = this.p;
@@ -183,9 +189,13 @@ class HfBitcrush extends AudioWorkletProcessor {
     this.p = o.processorOptions || {};
     this.holds = [];
     this.held = [];
-    this.port.onmessage = (e) => { this.p = { ...this.p, ...e.data }; };
+    this.port.onmessage = (e) => {
+      if (e.data && e.data.__hfDispose) { this.dead = true; return; }
+      this.p = { ...this.p, ...e.data };
+    };
   }
   process(inputs, outputs) {
+    if (this.dead) return false;
     const i = inputs[0], o = outputs[0];
     if (!i || !i.length) return true;
     const p = this.p;
@@ -243,7 +253,16 @@ export function ensureAudioFxWorklets(ctx: BaseAudioContext): Promise<void> {
       )}`;
       await ctx.audioWorklet.addModule(url);
       readyContexts.add(ctx);
-    })();
+    })().catch((err: unknown) => {
+      // A failed registration must not be remembered. `readyContexts` is only
+      // written on success, so callers correctly keep asking — and every ask
+      // replayed this same rejected promise, leaving the limiter, compressor,
+      // gate and bitcrush silent for the life of the context with no way back.
+      // One transient failure (a slow module load, a context still warming up)
+      // permanently disabled half the rack.
+      registered.delete(ctx);
+      throw err;
+    });
     registered.set(ctx, modulePromise);
   }
   return modulePromise;
diff --git a/packages/core/src/audioCarve.test.ts b/packages/core/src/audioCarve.test.ts
index c2cb26019..be4dcfb14 100644
--- a/packages/core/src/audioCarve.test.ts
+++ b/packages/core/src/audioCarve.test.ts
@@ -250,6 +250,48 @@ describe("analyseCarveBands", () => {
   });
 });
 
+/**
+ * Both analysis loops reuse one pair of FFT scratch arrays across every window
+ * rather than allocating a pair per hop — a 5-minute 48 kHz voiceover is ~7000
+ * hops, so ~460 MB of transient Float64Array used to churn through the main
+ * thread for one carve. `re` is fully overwritten each window, but `im` is only
+ * ever added to, so it has to be cleared; missing that, the imaginary part
+ * accumulates across windows and every spectrum after the first is wrong by a
+ * growing amount.
+ */
+describe("reused FFT scratch across windows", () => {
+  /** A steady tone on an exact bin centre (48000/4096 x 128), so every window is identical. */
+  const steady = (seconds: number): Float32Array => {
+    const n = Math.floor(SR * seconds);
+    const out = new Float32Array(n);
+    for (let i = 0; i < n; i++) out[i] = 0.5 * Math.sin((2 * Math.PI * 1500 * i) / SR);
+    return out;
+  };
+
+  it("measures the same bands however many windows the clip has", () => {
+    // Every window carries the same spectrum, so the Welch average cannot
+    // depend on how many were averaged — unless one window is contaminating
+    // the next.
+    const short = analyseCarveBands(steady(0.5), SR, PROFILE);
+    const long = analyseCarveBands(steady(12), SR, PROFILE);
+    expect(short.length).toBeGreaterThan(0);
+    expect(long).toEqual(short);
+  });
+
+  it("keeps a steady tone's dynamics envelope flat instead of drifting", () => {
+    const [lane] = analyseCarveDynamics(steady(12), SR, [{ freq: 1600, gainDb: -8, q: 1.4 }]);
+    const value = (t: number): number =>
+      sampleAutomationLane({ target: "fx.n1.gain", points: lane!.points }, t);
+    // Past the attack the cut has to sit still, because the signal does. A
+    // window contaminated by the one before it grows the measured power over
+    // the clip, and the envelope — which is relative to the band's own peak —
+    // slides with it.
+    expect(value(4)).toBeLessThan(-1);
+    expect(value(8)).toBeCloseTo(value(4), 0);
+    expect(value(11)).toBeCloseTo(value(4), 0);
+  });
+});
+
 describe("carveBandsToChain", () => {
   it("turns bands into peaking nodes carrying the analysed values", () => {
     const chain = carveBandsToChain([{ freq: 1000, gainDb: -6, q: 1.4 }]);
diff --git a/packages/core/src/audioCarve.ts b/packages/core/src/audioCarve.ts
index 080638c4c..265b48352 100644
--- a/packages/core/src/audioCarve.ts
+++ b/packages/core/src/audioCarve.ts
@@ -332,12 +332,23 @@ function powerSpectrum(
 
   const bins = FRAME / 2 + 1;
   const acc = new Float64Array(bins);
+  // Reused across hops. These used to be allocated inside the loop: a 5-minute
+  // 48 kHz voiceover is ~7000 hops, so ~460 MB of transient Float64Array
+  // churned through the main thread for a single carve. `re` is fully
+  // overwritten below; only `im` has to be cleared.
+  const re = new Float64Array(FRAME);
+  const im = new Float64Array(FRAME);
+  //
+  // Every hop is still read. Striding them — Welch's average is supposed to
+  // settle long before 7000 windows — was measured on a 5-minute voiceover and
+  // moves the result: at strength 0.9 the chosen band set changed (630 Hz for
+  // 160 Hz), and it did not converge back to the full read even at 2048
+  // windows. 27x faster is not worth silently redrawing the author's carve.
   let frames = 0;
   for (let start = 0; start + FRAME <= n; start += HOP) {
     // Goertzel-free naive DFT would be O(n^2); use a real FFT via recursion on
     // a copied frame. FRAME is a power of two so the radix-2 split is exact.
-    const re = new Float64Array(FRAME);
-    const im = new Float64Array(FRAME);
+    im.fill(0);
     for (let i = 0; i < FRAME; i++) re[i] = (padded[start + i] ?? 0) * window[i]!;
     fft(re, im);
     for (let k = 0; k < bins; k++) acc[k]! += re[k]! * re[k]! + im[k]! * im[k]!;
@@ -601,9 +612,13 @@ export function analyseCarveDynamics(
 
   const times: number[] = [];
   const perBand = bands.map(() => [] as number[]);
+  // Reused across windows, as in powerSpectrum. `re` is fully overwritten
+  // below; only `im` has to be cleared. The hop here is already bounded by
+  // POINT_BUDGET, so there is nothing to stride.
+  const re = new Float64Array(FRAME);
+  const im = new Float64Array(FRAME);
   for (let start = 0; start < voice.length; start += hop) {
-    const re = new Float64Array(FRAME);
-    const im = new Float64Array(FRAME);
+    im.fill(0);
     for (let i = 0; i < FRAME; i++) re[i] = (voice[start + i] ?? 0) * window[i]!;
     fft(re, im);
     const power: number[] = [];
diff --git a/packages/core/src/audioFx.test.ts b/packages/core/src/audioFx.test.ts
index e59819b95..3caaa2464 100644
--- a/packages/core/src/audioFx.test.ts
+++ b/packages/core/src/audioFx.test.ts
@@ -69,6 +69,27 @@ describe("normalizeAudioFxParams", () => {
     expect(v.gain).toBe(0);
   });
 
+  it("treats a blank or missing value as absent rather than as zero", () => {
+    // `Number(null)`, `Number("")`, `Number(false)` and `Number([])` are all 0
+    // and all finite, so these used to clamp to 0 instead of falling back. Zero
+    // is a legal setting for most of these knobs, so nothing downstream could
+    // tell: a compressor whose threshold arrived as null sat at 0 dB and never
+    // engaged, silently, rather than at its declared -24 dB.
+    const def = defaultAudioFxParams("compressor").threshold;
+    expect(def).not.toBe(0);
+    for (const blank of [null, undefined, "", "   ", false, [], {}]) {
+      expect(
+        normalizeAudioFxParams("compressor", { threshold: blank as unknown as number }).threshold,
+        `${JSON.stringify(blank)} was read as a number`,
+      ).toBe(def);
+    }
+    // A string that really does spell a number still counts — that is how the
+    // panel's inputs arrive.
+    expect(
+      normalizeAudioFxParams("compressor", { threshold: "-30" as unknown as number }).threshold,
+    ).toBe(-30);
+  });
+
   it("falls back to the default for an unrecognised enum value", () => {
     expect(normalizeAudioFxParams("saturate", { type: "sawtooth" }).type).toBe("tanh");
     expect(normalizeAudioFxParams("saturate", { type: "atan" }).type).toBe("atan");
diff --git a/packages/core/src/audioFx.ts b/packages/core/src/audioFx.ts
index 1e38c4f29..32be62bc6 100644
--- a/packages/core/src/audioFx.ts
+++ b/packages/core/src/audioFx.ts
@@ -761,7 +761,20 @@ export function normalizeAudioFxParams(
       out[p.key] = ok ? (raw as string) : p.default;
       continue;
     }
-    const n = typeof raw === "number" ? raw : Number(raw);
+    // Only a number, or a string that actually spells one. `Number(null)`,
+    // `Number("")`, `Number(false)` and `Number([])` are all 0 and all pass
+    // Number.isFinite, so a missing or blanked value used to clamp to 0 rather
+    // than fall back to the declared default — and 0 is a legal value for most
+    // of these knobs, so nothing downstream could tell. A compressor whose
+    // threshold arrived as null sat at 0 dB and never engaged, silently,
+    // instead of at its -24 dB default. `numberOrNull` in audioAutomation.ts
+    // already guards exactly this.
+    const n =
+      typeof raw === "number"
+        ? raw
+        : typeof raw === "string" && raw.trim() !== ""
+          ? Number(raw)
+          : Number.NaN;
     out[p.key] = Number.isFinite(n) ? Math.min(p.max, Math.max(p.min, n)) : p.default;
   }
   return out;
diff --git a/packages/producer/src/services/render/stages/audioStage.test.ts b/packages/producer/src/services/render/stages/audioStage.test.ts
index 7be552b08..ffa0b9715 100644
--- a/packages/producer/src/services/render/stages/audioStage.test.ts
+++ b/packages/producer/src/services/render/stages/audioStage.test.ts
@@ -122,7 +122,27 @@ describe("runAudioStage", () => {
     const result = await runAudioStage(makeInput());
     expect(result.hasAudio).toBe(false);
     expect(result.audioError).toMatch(/Audio FX failed for track bgm/);
-    expect(result.audioFailures).toBeUndefined();
+    // And it is classified. This used to come back undefined, so the warning
+    // policy — which reads owner, retryability, reason and stage off this list
+    // — described the FATAL failure with strictly less detail than a single
+    // dropped track gets.
+    expect(result.audioFailures).toEqual([
+      {
+        stage: "internal",
+        reason: "internal",
+        owner: "system",
+        retryable: false,
+        detail: "Audio FX failed for track bgm: browser launch failed",
+      },
+    ]);
+  });
+
+  it("bounds the synthesised failure's detail", async () => {
+    // `detail` is contractually bounded diagnostic text; an ffmpeg-flavoured
+    // message can run to tens of kilobytes.
+    processCompositionAudioMock.mockRejectedValue(new Error("x".repeat(5_000)));
+    const result = await runAudioStage(makeInput());
+    expect(result.audioFailures?.[0]?.detail.length).toBe(2_000);
   });
 
   it("lets an abort keep its own shape rather than becoming an audio error", async () => {
diff --git a/packages/producer/src/services/render/stages/audioStage.ts b/packages/producer/src/services/render/stages/audioStage.ts
index ac243dd82..5e61a4a17 100644
--- a/packages/producer/src/services/render/stages/audioStage.ts
+++ b/packages/producer/src/services/render/stages/audioStage.ts
@@ -90,12 +90,28 @@ export async function runAudioStage(input: AudioStageInput): Promise<AudioStageR
     } catch (err) {
       // An abort is the caller's own signal and must keep its own shape.
       assertNotAborted();
+      const detail = err instanceof Error ? err.message : String(err);
       return {
         audioOutputPath,
         hasAudio: false,
         audioProcessMs: Date.now() - stage3Start,
-        audioError: err instanceof Error ? err.message : String(err),
-        audioFailures: undefined,
+        audioError: detail,
+        // Synthesised rather than left undefined. The warning policy reads
+        // owner, retryability, reason and stage off this list, so reporting the
+        // FATAL failure — the one that took the whole mix down — with an empty
+        // one gave it strictly less classification than a single dropped track
+        // gets, which is the opposite of what this stage exists to do.
+        // "internal" is the honest bucket: the stages enumerate ffmpeg steps
+        // and this is the FX render, which is none of them.
+        audioFailures: [
+          {
+            stage: "internal",
+            reason: "internal",
+            owner: "system",
+            retryable: false,
+            detail: detail.slice(0, 2_000),
+          },
+        ],
       };
     }
     assertNotAborted();