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/__fixtures__/fakeS3.ts

@@ -0,0 +1,69 @@
+/**
+ * Shared `FakeS3` for the SDK unit tests.
+ *
+ * Multiple SDK tests need to assert what `deploySite` / `renderToLambda`
+ * sent to S3. Each fake here records `HeadObjectCommand` + `PutObjectCommand`
+ * activity and drains the body stream so the lazy `createReadStream`
+ * inside `uploadFileToS3` doesn't try to open the workdir tarball after
+ * `deploySite`'s `finally` block has rmSync'd it.
+ */
+
+import type { S3Client } from "@aws-sdk/client-s3";
+
+export interface FakeS3Op {
+  kind: "head" | "put";
+  bucket: string;
+  key: string;
+}
+
+export class FakeS3 {
+  ops: FakeS3Op[] = [];
+  existing = new Set<string>();
+
+  async send(command: unknown): Promise<unknown> {
+    const cmdName = (command as { constructor: { name: string } }).constructor.name;
+    const input = (command as { input: { Bucket: string; Key: string } }).input;
+    if (cmdName === "HeadObjectCommand") {
+      this.ops.push({ kind: "head", bucket: input.Bucket, key: input.Key });
+      if (this.existing.has(`${input.Bucket}/${input.Key}`)) {
+        return { ContentLength: 1, LastModified: new Date("2026-05-16T00:00:00Z") };
+      }
+      const err = new Error("Not Found") as Error & {
+        $metadata: { httpStatusCode: number };
+        name: string;
+      };
+      err.name = "NotFound";
+      err.$metadata = { httpStatusCode: 404 };
+      throw err;
+    }
+    if (cmdName === "PutObjectCommand") {
+      this.ops.push({ kind: "put", bucket: input.Bucket, key: input.Key });
+      this.existing.add(`${input.Bucket}/${input.Key}`);
+      await drainBody((command as { input: { Body: NodeJS.ReadableStream | Buffer } }).input.Body);
+      return {};
+    }
+    throw new Error(`FakeS3: unexpected command ${cmdName}`);
+  }
+}
+
+/** Convenience cast so `deploySite({ s3: makeFakeS3() })` reads cleanly. */
+export function asS3Client(fake: FakeS3): S3Client {
+  return fake as unknown as S3Client;
+}
+
+/**
+ * Consume the body stream to completion. Without this, the lazy
+ * `createReadStream` opened inside `uploadFileToS3` would attempt to
+ * read the workdir tarball after deploySite's `finally` block removed
+ * the workdir — surfacing as an "Unhandled error between tests"
+ * teardown noise that bun's runner attributes to the next test.
+ */
+async function drainBody(body: NodeJS.ReadableStream | Buffer): Promise<void> {
+  if (Buffer.isBuffer(body)) return;
+  await new Promise<void>((resolve, reject) => {
+    body.on("data", () => {});
+    body.on("end", () => resolve());
+    body.on("close", () => resolve());
+    body.on("error", reject);
+  });
+}