refactor(producer): simplify — extract HDR compositor, delete dead code, consolidate patterns (#1414)

* refactor(producer): extract HDR compositor from renderOrchestrator

Move ~700 LOC of HDR compositing primitives (countNonZeroAlpha,
countNonZeroRgb48, cropRgb48le, HdrVideoFrameSource,
closeHdrVideoFrameSource, blitHdrVideoLayer, HdrImageBuffer,
blitHdrImageLayer, CompositeTransfer, shouldUseLayeredComposite,
resolveCompositeTransfer, HdrCompositeContext, compositeHdrFrame,
HdrTransitionMeta, TransitionRange) into a dedicated
hdrCompositor.ts module.

Remove backward-compat re-exports from renderOrchestrator (hdrPerf,
captureCost, shared) and rewire all import sites to the
authoritative source modules.

* refactor(producer): delete 4 re-export shim files

screenshotService.ts, videoFrameExtractor.ts, videoFrameInjector.ts,
and streamingEncoder.ts existed solely to re-export symbols from
@hyperframes/engine. No internal consumer imported from them except
index.ts → videoFrameInjector, which now imports directly from engine.

* refactor(producer): delete unused PNG decode/blit worker pool

The pool (455 LOC) and worker (127 LOC) were built speculatively for
pipelining Chrome screenshots with PNG decode/blit but were never
wired into any capture path. Zero non-test source files imported them.

Also removed the esbuild entry point from producer/build.mjs, the
tsup entry point + alpha-blit alias from cli/tsup.config.ts, and
the PNG worker bootstrap from cli/src/cli.ts.

* refactor(producer): centralize frame filename construction

Replace 4 inline padStart(6) template literals with shared helpers:
- formatCaptureFrameName(index, ext): zero-based, for internal capture
- formatExportFrameName(index, ext): zero-based input, one-based output
  for user-facing png-sequence export

* perf(producer): hoist allElementIds out of compositing loop

Move fullStacking.map() from inside the per-layer iteration to before
the loop, computing the element ID list once per frame instead of once
per DOM layer per frame.

* refactor(producer): consolidate HDR timing instrumentation

* refactor(producer): remove typecasts and deduplicate HDR capture patterns

- Extract seekInjectAndQueryStacking() and seekAndInject() helpers to
  deduplicate the seek+inject+query pattern across sequential loop,
  hybrid loop, and per-scene transition capture (3 call sites → 1 helper)
- Fix sceneBuf as Buffer casts by properly typing the scene-capture
  arrays as [Buffer, Set<string>][] instead of using as const + cast
- Replace as NonNullable<> cast on outputFormat with as const fallback
- Add explanatory comments on inherent linkedom DOM casts

* refactor(producer): name constants, type matrix, extract opacity helper

- Replace magic 0.001/0.999 with TRANSFORM_IDENTITY_EPSILON and
  OPAQUE_ALPHA_THRESHOLD; replace BPP=6 with RGB48_BYTES_PER_PIXEL
- Add AffineMatrix tuple type + isAffineMatrix guard, eliminating
  all 4 non-null assertions on matrix indices
- Extract resolveBlitOpacity() to replace 5 identical ternaries
- Narrow fallow-ignore-file to line-level complexity suppressions

packages/producer/src/utils/paths.test.ts

@@ -14,7 +14,12 @@
 import { describe, expect, it } from "vitest";
 import { resolve, win32 } from "node:path";
 
-import { isPathInside, toExternalAssetKey } from "./paths.js";
+import {
+  isPathInside,
+  toExternalAssetKey,
+  formatCaptureFrameName,
+  formatExportFrameName,
+} from "./paths.js";
 
 describe("isPathInside", () => {
   it("returns true when child is directly inside parent", () => {
@@ -133,3 +138,27 @@ describe("toExternalAssetKey", () => {
     expect(/^[A-Za-z]:/.test(key)).toBe(false);
   });
 });
+
+describe("formatCaptureFrameName", () => {
+  it("returns zero-padded filename for zero-based index", () => {
+    expect(formatCaptureFrameName(0, "jpg")).toBe("frame_000000.jpg");
+  });
+
+  it("pads to 6 digits for large indices", () => {
+    expect(formatCaptureFrameName(999999, "png")).toBe("frame_999999.png");
+  });
+
+  it("handles mid-range indices", () => {
+    expect(formatCaptureFrameName(42, "jpg")).toBe("frame_000042.jpg");
+  });
+});
+
+describe("formatExportFrameName", () => {
+  it("returns one-based filename from zero-based input", () => {
+    expect(formatExportFrameName(0, "png")).toBe("frame_000001.png");
+  });
+
+  it("increments index by 1", () => {
+    expect(formatExportFrameName(4, "png")).toBe("frame_000005.png");
+  });
+});

packages/producer/src/utils/paths.ts

@@ -109,6 +109,14 @@ export function toExternalAssetKey(absPath: string): string {
   return "hf-ext/" + normalised;
 }
 
+export function formatCaptureFrameName(index: number, ext: string): string {
+  return `frame_${String(index).padStart(6, "0")}.${ext}`;
+}
+
+export function formatExportFrameName(index: number, ext: string): string {
+  return `frame_${String(index + 1).padStart(6, "0")}.${ext}`;
+}
+
 export function resolveRenderPaths(
   projectDir: string,
   outputPath: string | null | undefined,