Address @claude review: format core/, typed output-validation error, document progress heuristic

- Run Prettier on the 60 core/ files this PR touched — the deterministic
  import rewrite had collapsed multi-line imports and left throws unwrapped;
  core/ is in no format gate so it slipped past CI. Now Prettier-clean.
- Default-path output-schema violation now throws
  ProtocolError(ProtocolErrorCode.InvalidParams, …) instead of a bare Error,
  matching the prior v1 contract (SDK threw a typed McpError with a code) so
  downstream `instanceof`/`.code` branching keeps working.
- Document the "assumes serial construction" invariant on pollTaskToolCall's
  progress-subscription revival (the `_progressHandlers` new-key heuristic).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core/mcp/toolOutputValidation.ts

@@ -1,5 +1,8 @@
 import type { CallToolResult, Tool } from "@modelcontextprotocol/client";
-import type { JsonSchemaType, jsonSchemaValidator } from "@modelcontextprotocol/client";
+import type {
+  JsonSchemaType,
+  jsonSchemaValidator,
+} from "@modelcontextprotocol/client";
 
 /**
  * Validate a delivered tool result's `structuredContent` against the tool's