feat: pluggable reply/forward quote header #295

lib/plugin-types.ts

@@ -645,6 +645,52 @@ export interface ReplyContext {
   mode: 'reply' | 'reply-all' | 'forward';
 }
 
+/**
+ * Second argument to onBuildQuoteHeader transform handlers. Describes the
+ * original message and how the host plans to render the quote header so
+ * plugins can produce a replacement block (e.g. an Outlook-style
+ * From/Sent/To/Cc/Subject section).
+ */
+export interface QuoteHeaderContext {
+  mode: 'reply' | 'replyAll' | 'forward';
+  /** Recipients of the new outgoing message (already resolved by the host). */
+  newTo: string[];
+  newCc: string[];
+  /** Original message metadata. */
+  from: { name?: string; email: string } | null;
+  to: { name?: string; email: string }[];
+  cc: { name?: string; email: string }[];
+  subject: string;
+  /** Pre-formatted date string the host already produced (locale-aware). */
+  date: string;
+  /** Raw ISO datetime, in case the plugin wants to reformat. */
+  receivedAt?: string;
+  /** Active UI locale (BCP-47), useful for Intl.DateTimeFormat in plugins. */
+  locale: string;
+}
+
+/**
+ * Initial value for the onBuildQuoteHeader transform hook. Plugins return a
+ * replacement; returning undefined falls through to the next handler or the
+ * default. The composer splices `html` into HTML drafts and `text` into
+ * plain-text drafts.
+ *
+ * For HTML, returning a header that includes its own surrounding wrapper
+ * (`<div>...</div>`) is fine; the composer does not add extra wrappers.
+ * For text, the host appends the quoted body after the header.
+ */
+export interface QuoteHeader {
+  html: string;
+  text: string;
+  /**
+   * When false, the composer skips its default blockquote wrapping around the
+   * quoted body (HTML mode only). Use this for the Outlook style where the
+   * quoted message is intended to follow the header without indentation.
+   * Defaults to true (preserve the existing blockquote wrapping).
+   */
+  wrapInBlockquote?: boolean;
+}
+
 /**
  * Describes an attachment crossing an attachment hook (upload, download, preview).
  */