refactor(javascript): MessageProcessor abstraction added and implemented in catcher event processing pipeline

- MessageProcessor interface and MessageHint type
- BrowserMessageProcessor, BreadcrumbsMessageProcessor, ConsoleCatcherMessageProcessor, DebugMessageProcessor
- replaced inline addon logic with sequential MessageProcessor pipeline

Author: Reversean

packages/core/src/index.ts

@@ -13,3 +13,5 @@ export { buildElementSelector } from './utils/selector';
 export { EventRejectedError } from './errors';
 export { isErrorProcessed, markErrorAsProcessed } from './utils/event';
 export type { BreadcrumbStore, BreadcrumbsAPI, BreadcrumbHint, BreadcrumbInput } from './breadcrumbs/breadcrumb-store';
+export type { MessageHint, MessageProcessor, ProcessingPayload } from './messages/message-processor';
+export { BreadcrumbsMessageProcessor } from './messages/breadcrumbs-message-processor';;

packages/core/src/messages/breadcrumbs-message-processor.ts

@@ -0,0 +1,24 @@
+import type { MessageHint, MessageProcessor, ProcessingPayload } from './message-processor';
+
+/**
+ * Attaches breadcrumbs snapshot from {@link hint} to payload.
+ */
+export class BreadcrumbsMessageProcessor implements MessageProcessor<'errors/javascript'> {
+  /**
+   * Sets `payload.breadcrumbs` from hint snapshot if non-empty; skips otherwise.
+   *
+   * @param payload - event message payload to enrich
+   * @param hint - hint carrying breadcrumbs snapshot captured at error time
+   * @returns modified payload with breadcrumbs set, or original payload unchanged
+   */
+  public apply(
+    payload: ProcessingPayload<'errors/javascript'>,
+    hint?: MessageHint
+  ): ProcessingPayload<'errors/javascript'> | null {
+    if (hint?.breadcrumbs && hint.breadcrumbs.length > 0) {
+      payload.breadcrumbs = hint.breadcrumbs;
+    }
+
+    return payload;
+  }
+}

packages/core/src/messages/message-processor.ts

@@ -0,0 +1,57 @@
+import type { Breadcrumb, CatcherMessagePayload, CatcherMessageType } from '@hawk.so/types';
+
+/**
+ * Extracted addons type from catcher message payload.
+ *
+ * @typeParam T - catcher message type
+ */
+type ExtractAddons<T extends CatcherMessageType> =
+  CatcherMessagePayload<T> extends { addons?: infer A } ? A : never;
+
+/**
+ * Payload type used during message processing pipeline.
+ *
+ * Same as {@link CatcherMessagePayload} but with `addons` always defined and partially filled —
+ * processors may contribute individual addon fields independently of each other.
+ *
+ * @typeParam T - catcher message type this payload belongs to
+ */
+export type ProcessingPayload<T extends CatcherMessageType> =
+  Omit<CatcherMessagePayload<T>, 'addons'> & {
+    addons: Partial<ExtractAddons<T>>;
+  };
+
+/**
+ * Snapshot of event context captured synchronously at error time,
+ * before any processing.
+ */
+export interface MessageHint {
+  /**
+   * Original caught error.
+   */
+  error?: Error | string;
+
+  /**
+   * Breadcrumbs captured at error time.
+   */
+  breadcrumbs?: Breadcrumb[];
+}
+
+/**
+ * Single step in message processing pipeline before message is sent.
+ *
+ * @typeParam T - catcher message type this processor handles
+ */
+export interface MessageProcessor<T extends CatcherMessageType = CatcherMessageType> {
+  /**
+   * Handles input message. May mutate or replace it.
+   *
+   * @param payload - processed event message payload with partially-built addons
+   * @param hint - additional context about original error
+   * @returns modified payload, or `null` to drop event
+   */
+  apply(
+    payload: ProcessingPayload<T>,
+    hint?: MessageHint,
+  ): ProcessingPayload<T> | null
+}

packages/core/src/modules/sanitizer.ts

@@ -154,7 +154,6 @@ export class Sanitizer {
     depth: number,
     seen: WeakSet<object>
   ): Record<string, any> | '<deep object>' | '<big object>' {
-
     // If the maximum depth is reached, return a placeholder
     if (depth > Sanitizer.maxDepth) {
       return '<deep object>';