fix(aws-lambda): widen narrow format types to include webm

CI on PR #951 was failing at typecheck/build because the producer's
`DistributedRenderConfig.format` widened to include webm in this PR
but the aws-lambda package's narrow `"mp4" | "mov" | "png-sequence"`
type literals in `events.ts`, `handler.ts`, and `validateConfig.ts`
hadn't kept up. `renderToLambda.ts:87` passed `config.format` (now
including webm) into a parameter typed against the narrow union,
producing TS2345.

This widening originally landed in PR #952 (test fixture PR) but
needs to be atomic with the producer's widening here to keep each
PR independently typecheck-clean.

Also refactor `formatExtension` from a switch dispatch to a
`Record<DistributedFormat, string>` lookup. Adding the webm case
tipped the switch's CRAP to the 30.0 fallow threshold; the lookup
table drops cyclomatic from 5 to 1 with the same compile-time
exhaustiveness guarantee (TS errors on missing entries when
`DistributedFormat` adds a new format). The runtime
`_exhaustive: never` throw was only protecting against a string
slipping past TS; `validateConfig.ts`'s `ALLOWED_FORMATS` already
gates untrusted input at the SDK boundary.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jrusso1020

packages/aws-lambda/src/events.ts

@@ -65,7 +65,7 @@ export interface RenderChunkEvent {
   /** S3 URI prefix where the chunk output should be uploaded (`s3://bucket/{prefix}/`). */
   ChunkOutputS3Prefix: string;
   /** Output container format from the plan's encoder.json; drives file vs frame-dir handling. */
-  Format: "mp4" | "mov" | "png-sequence";
+  Format: "mp4" | "mov" | "png-sequence" | "webm";
 }
 
 /** Activity C: fetch planDir + all chunks + audio, assemble, upload final. */
@@ -80,7 +80,7 @@ export interface AssembleEvent {
   /** Final output S3 URI (`s3://bucket/key.mp4`). */
   OutputS3Uri: string;
   /** Output container format; drives file vs frame-dir handling. */
-  Format: "mp4" | "mov" | "png-sequence";
+  Format: "mp4" | "mov" | "png-sequence" | "webm";
 }
 
 /**
@@ -106,7 +106,7 @@ export interface PlanLambdaResult {
   Fps: 24 | 30 | 60;
   Width: number;
   Height: number;
-  Format: "mp4" | "mov" | "png-sequence";
+  Format: "mp4" | "mov" | "png-sequence" | "webm";
   HasAudio: boolean;
   AudioS3Uri: string | null;
   FfmpegVersion: string;

packages/aws-lambda/src/formatExtension.ts

@@ -6,19 +6,20 @@
  * looks like vs a png-sequence.
  */
 
-export type DistributedFormat = "mp4" | "mov" | "png-sequence";
+export type DistributedFormat = "mp4" | "mov" | "png-sequence" | "webm";
+
+// Closed-enum lookup table. TS enforces exhaustiveness via the
+// `Record<DistributedFormat, string>` annotation — adding a format to
+// `DistributedFormat` without adding the matching key here fails to
+// typecheck, which is the same exhaustiveness guarantee a switch +
+// `_exhaustive: never` arm provides but at lower complexity.
+const FORMAT_EXTENSIONS: Record<DistributedFormat, string> = {
+  mp4: ".mp4",
+  mov: ".mov",
+  webm: ".webm",
+  "png-sequence": "",
+};
 
 export function formatExtension(format: DistributedFormat): string {
-  switch (format) {
-    case "mp4":
-      return ".mp4";
-    case "mov":
-      return ".mov";
-    case "png-sequence":
-      return "";
-    default: {
-      const _exhaustive: never = format;
-      throw new Error(`[formatExtension] unsupported format: ${_exhaustive as string}`);
-    }
-  }
+  return FORMAT_EXTENSIONS[format];
 }

packages/aws-lambda/src/handler.ts

@@ -433,7 +433,7 @@ async function downloadChunkObjects(
   s3: S3Client,
   uris: string[],
   workDir: string,
-  format: "mp4" | "mov" | "png-sequence",
+  format: "mp4" | "mov" | "png-sequence" | "webm",
 ): Promise<string[]> {
   const chunksDir = join(workDir, "chunks");
   mkdirSync(chunksDir, { recursive: true });

packages/aws-lambda/src/sdk/validateConfig.test.ts

@@ -54,7 +54,7 @@ describe("validateDistributedRenderConfig", () => {
       "unsupported format",
       {
         ...VALID,
-        format: "webm",
+        format: "gif",
       } as unknown as SerializableDistributedRenderConfig,
       "config.format",
     ],

packages/aws-lambda/src/sdk/validateConfig.ts

@@ -31,7 +31,7 @@ export class InvalidConfigError extends Error {
 }
 
 const ALLOWED_FPS = [24, 30, 60] as const;
-const ALLOWED_FORMATS = ["mp4", "mov", "png-sequence"] as const;
+const ALLOWED_FORMATS = ["mp4", "mov", "png-sequence", "webm"] as const;
 const ALLOWED_CODECS = ["h264", "h265"] as const;
 const ALLOWED_QUALITIES = ["draft", "standard", "high"] as const;
 const ALLOWED_RUNTIME_CAPS = ["lambda", "temporal", "cloud-run-job", "k8s-job", "none"] as const;