feat: Node Slack SDK major version release candidate (#2603)

Co-authored-by: Claude <svc-devxp-claude@slack-corp.com>
Co-authored-by: Eden Zimbelman <eden.zimbelman@salesforce.com>
Co-authored-by: Ale Mercado <104795114+srtaalej@users.noreply.github.com>
Co-authored-by: Luke Russell <31357343+lukegalbraithrussell@users.noreply.github.com>

Author: 5 people

.changeset/drop-node18-cli-hooks.md

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+---
+"@slack/cli-hooks": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/drop-node18-cli-test.md

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+---
+"@slack/cli-test": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/drop-node18-logger.md

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+---
+"@slack/logger": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/drop-node18-oauth.md

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+---
+"@slack/oauth": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/drop-node18-socket-mode.md

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+---
+"@slack/socket-mode": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/drop-node18-types.md

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+---
+"@slack/types": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/drop-node18-web-api.md

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+---
+"@slack/web-api": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/drop-node18-webhook.md

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+---
+"@slack/webhook": major
+---
+
+Drop Node.js 18 support. The minimum supported Node.js version is now 20.

.changeset/manifest-agent-view.md

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+---
+"@slack/web-api": minor
+---
+
+feat: expand app manifest types — add `agent_view` and `assistant_view` features, recent agent events (`app_context_changed`, `assistant_thread_started`, `assistant_thread_context_changed`), optional OAuth scopes (`bot_optional`/`user_optional`), and event `metadata_subscriptions`

.changeset/oauth-error-classes.md

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+---
+"@slack/oauth": major
+---
+
+Error classes now extend a new `SlackOAuthError` abstract base class (which extends `Error`), bringing `@slack/oauth` in line with the error handling in `@slack/web-api` and `@slack/webhook`. You can catch any error thrown by this package with `if (error instanceof SlackOAuthError)`, in addition to the existing per-class `instanceof` checks (`AuthorizationError`, `InstallerInitializationError`, etc.).
+
+`AuthorizationError` now populates the standard [`Error.cause`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause) property with the underlying error when one is available (for example, the failure that caused `authorize()` to reject). The existing `original` property is still present and carries the same value.
+
+```javascript
+import { AuthorizationError } from '@slack/oauth';
+
+try {
+  await installer.authorize({ teamId, enterpriseId });
+} catch (error) {
+  if (error instanceof AuthorizationError) {
+    console.log(error.cause);    // the underlying error
+    console.log(error.original); // same value — kept for backward compat
+  }
+}
+```
+
+The `error.code` property and `ErrorCode` enum values are unchanged, so existing `error.code` checks continue to work. The `CodedError` interface is retained (it is part of the public `CallbackOptions#failure` callback signature), but for new code we recommend `instanceof` checks against `SlackOAuthError` or a specific subclass.
+
+Note: `error.name` now reflects the specific class name (e.g. `'AuthorizationError'`) instead of the generic `'Error'`. If you branch on `error.name`, update those checks accordingly.