fix(edge): preserve JSON-RPC batch envelopes - #321

Summary

Preserve the JSON-RPC batch envelope in the Edge transport based on the shape of the original request, rather than the number of response objects that remain after notifications are omitted.

This follows JSON-RPC 2.0 batch semantics:

• every non-empty batch response is an array, even when the batch contains one request or only one response survives;
• an empty batch ([]) is invalid and returns one response object (not an array) with HTTP 200, error -32600, and id: null;
• a batch containing only notifications keeps the existing HTTP 202 response with no body or content type;
• mixed batches omit notifications, preserve the current sequential response order, and return HTTP 200 with application/json;
• non-batch requests continue to return a single response object.

Implementation

• Record whether the parsed request body was an array before normalizing it into messages.
• Reject an empty array before the notification-only 202 path.
• Serialize responses according to the original request shape.
• Add regressions for a one-request batch and an empty batch.

The diff is limited to src/edge/index.ts and src/edge/edge.test.ts; package manifests and the lockfile are unchanged. This branch is based directly on main at v4.14.4 after #320 merged.

Verification

Fresh RED on v4.14.4 with the tests only:

• one-request batch returned an object instead of an array;
• [] returned HTTP 202 instead of an Invalid Request object.

GREEN on this head:

• focused batch regressions: 2/2;
• complete Edge suite: 17/17;
• complete test suite: 45 files, 553/553;
• tsc --noEmit: pass;
• ESLint: pass;
• Prettier on both touched files: pass;
• ESM/CJS/DTS build: pass;
• JSR publish dry-run: pass;
• runtime probe for mixed batches, notification-only batches, response order, status codes, content type, and single-request envelope: pass.