feat(lambda): add TypeScript SDK and CDK construct (#909)

* feat(lambda): add TypeScript SDK and CDK construct

Adds the client-side surface on top of the Phase 6a Lambda handler so
adopters can drive a deployed stack from Node without writing AWS-SDK
boilerplate:

- renderToLambda(opts) starts a Step Functions execution and returns a
  handle. Does NOT poll.
- getRenderProgress({ executionArn }) returns a snapshot of progress,
  frames rendered, cost (Lambda GB-seconds + SFN transitions), errors,
  and the final output object once Assemble completes.
- deploySite({ projectDir, bucketName }) content-addresses the project
  tree, tar.gzs it, and uploads to S3 with a HeadObject short-circuit so
  re-renders of the same tree skip the tar+PUT.
- validateDistributedRenderConfig throws a typed InvalidConfigError
  before StartExecution, so shape errors surface synchronously.
- computeRenderCost is exposed for callers who want to format cost out
  of band.

Also ships HyperframesRenderStack, an aws-cdk-lib L2 construct that
emits the same topology as examples/aws-lambda/template.yaml. Lives on
the ./cdk subpath export so SDK-only consumers don't pull aws-cdk-lib
into their runtime graph (declared as an optional peer dependency).

Tests: 24 new unit tests across the SDK plus 9 CDK synth / contract /
snapshot tests. All 83 tests in packages/aws-lambda/src pass.

* refactor(lambda): /simplify pass on the SDK + CDK PR

Pulls shared logic out so the SDK doesn't re-invent things the handler
and the producer already have:

- `formatExtension` extracted to packages/aws-lambda/src/formatExtension.ts.
  handler.ts and renderToLambda.ts both used identical 12-line copies of
  this switch.
- `PLAN_PROJECT_DIR_SKIP_SEGMENTS` is now exported from
  @hyperframes/producer/distributed. deploySite consumes it instead of
  its own duplicate SKIP_TOP_LEVEL set; the two lists were trivially
  identical and would have drifted silently.
- `FakeS3` + `drainBody` factored out of the two SDK test files into
  src/sdk/__fixtures__/fakeS3.ts. Drops ~110 lines of test-file
  duplication and gives future SDK tests a one-line FakeS3 import.
- S3 URI building in deploySite and renderToLambda routes through the
  existing `formatS3Uri` helper instead of inline `s3://...`
  concatenation; matches the convention already in handler.ts.

Net -133 lines across the touched files. All 83 aws-lambda tests still
pass; all 60 producer distributed tests still pass.

* fix(lambda): bump CDK test timeouts for CI cold-start synth

The bun:test default 5s timeout tripped the first CDK snapshot test
in CI when the cold-start `Template.fromStack(stack)` synth took ~5-8s
on the slowest GitHub Actions runner. Locally on a warm shell the
synth measures <1s, so the failure didn't reproduce until PR #909 hit
CI.

Two changes:

  - Both CDK test files cache one synth in `beforeAll(..., 30000)` and
    reuse the result across every test that uses the default props.
    Each individual test now runs in microseconds (pure assertions
    against the already-synthed template), so the 5s timeout no longer
    applies on the hot path.

  - The two contract tests that exercise non-default props
    (reservedConcurrency, projectName) still synth fresh per-test; they
    get a per-test `it(..., 30000)` timeout.

No behavior changes.

* fix(lambda): address PR review on SDK + CDK construct

Three correctness + ergonomics fixes raised in Vai's review:

  - getRenderProgress over-counted SFN transitions by 3-5×. Step
    Functions Standard Workflows bill per state-entry, not per
    history event. Each Task produces ~5-7 history events
    (Scheduled / Started / Succeeded / TaskStateExited / …);
    counting `events.length` reported the runaway. Switch to
    counting `*StateEntered` events explicitly.

  - assembleComplete + outputFile detection was coupled to the
    Lambda payload's `Action` field. Move both signals onto the
    enclosing state name (`StateExited.name === "Assemble"`), which
    is the state-machine identity rather than the Lambda event
    contract. framesRendered increment moves to the same boundary
    (RenderChunk state).

  - SiteHandle now carries `bucketName` directly so README + CLI
    callers don't have to re-parse `projectS3Uri.split("/")[2]`.

Test updates: getRenderProgress tests wrap renderChunk/assemble
events in matching StateEntered + StateExited pairs so the new
state-name-driven dispatch is exercised end-to-end. SiteHandle
fixture in renderToLambda.test.ts gets the new bucketName field.

All 83 aws-lambda tests still pass.

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

@@ -0,0 +1,130 @@
+import { describe, expect, it } from "bun:test";
+import type { SerializableDistributedRenderConfig } from "../events.js";
+import { InvalidConfigError, validateDistributedRenderConfig } from "./validateConfig.js";
+
+const VALID: SerializableDistributedRenderConfig = {
+  fps: 30,
+  width: 1920,
+  height: 1080,
+  format: "mp4",
+};
+
+describe("validateDistributedRenderConfig", () => {
+  it("returns the same reference on the happy path", () => {
+    expect(validateDistributedRenderConfig(VALID)).toBe(VALID);
+  });
+
+  it("accepts optional fields when valid", () => {
+    const cfg: SerializableDistributedRenderConfig = {
+      ...VALID,
+      codec: "h265",
+      quality: "high",
+      crf: 18,
+      chunkSize: 240,
+      maxParallelChunks: 16,
+      runtimeCap: "lambda",
+      hdrMode: "force-sdr",
+    };
+    expect(validateDistributedRenderConfig(cfg)).toBe(cfg);
+  });
+
+  it.each([
+    ["null config", null as unknown as SerializableDistributedRenderConfig, "config"],
+    [
+      "wrong fps",
+      { ...VALID, fps: 25 as 24 | 30 | 60 } satisfies SerializableDistributedRenderConfig,
+      "config.fps",
+    ],
+    [
+      "non-integer width",
+      { ...VALID, width: 1280.5 } satisfies SerializableDistributedRenderConfig,
+      "config.width",
+    ],
+    [
+      "odd width (yuv420p parity)",
+      { ...VALID, width: 1281 } satisfies SerializableDistributedRenderConfig,
+      "config.width",
+    ],
+    [
+      "out-of-range height",
+      { ...VALID, height: 8000 } satisfies SerializableDistributedRenderConfig,
+      "config.height",
+    ],
+    [
+      "unsupported format",
+      {
+        ...VALID,
+        format: "webm",
+      } as unknown as SerializableDistributedRenderConfig,
+      "config.format",
+    ],
+    [
+      "codec with non-mp4 format",
+      { ...VALID, format: "mov", codec: "h264" } satisfies SerializableDistributedRenderConfig,
+      "config.codec",
+    ],
+    [
+      "unknown codec",
+      {
+        ...VALID,
+        codec: "av1",
+      } as unknown as SerializableDistributedRenderConfig,
+      "config.codec",
+    ],
+    [
+      "crf + bitrate together",
+      { ...VALID, crf: 18, bitrate: "10M" } satisfies SerializableDistributedRenderConfig,
+      "config.crf",
+    ],
+    [
+      "crf out of range",
+      { ...VALID, crf: 60 } satisfies SerializableDistributedRenderConfig,
+      "config.crf",
+    ],
+    [
+      "malformed bitrate",
+      { ...VALID, bitrate: "fast" } satisfies SerializableDistributedRenderConfig,
+      "config.bitrate",
+    ],
+    [
+      "non-positive chunkSize",
+      { ...VALID, chunkSize: 0 } satisfies SerializableDistributedRenderConfig,
+      "config.chunkSize",
+    ],
+    [
+      "chunkSize over Lambda ceiling",
+      { ...VALID, chunkSize: 9999 } satisfies SerializableDistributedRenderConfig,
+      "config.chunkSize",
+    ],
+    [
+      "maxParallelChunks 0",
+      { ...VALID, maxParallelChunks: 0 } satisfies SerializableDistributedRenderConfig,
+      "config.maxParallelChunks",
+    ],
+    [
+      "unknown runtimeCap",
+      {
+        ...VALID,
+        runtimeCap: "azure",
+      } as unknown as SerializableDistributedRenderConfig,
+      "config.runtimeCap",
+    ],
+    [
+      "force-hdr rejected",
+      {
+        ...VALID,
+        hdrMode: "force-hdr",
+      } as unknown as SerializableDistributedRenderConfig,
+      "config.hdrMode",
+    ],
+  ])("rejects %s with field=%s", (_label, input, expectedField) => {
+    try {
+      validateDistributedRenderConfig(input);
+      throw new Error("expected validateDistributedRenderConfig to throw");
+    } catch (err) {
+      expect(err).toBeInstanceOf(InvalidConfigError);
+      expect((err as InvalidConfigError).field).toBe(expectedField);
+      expect((err as InvalidConfigError).name).toBe("InvalidConfigError");
+    }
+  });
+});