feat: Add unified reader settings with local overrides (#2230)

* Add initial impl

* fix some format inconsistencies, add indicator in user settings when local is out of sync

* Fix sliders in user settings, unify constants and formatting

* address CodeRabbit suggestions

* add mobile implementation

* address coderabbit nitpicks

* fix responsiveness of the reader settings popover

* Move more of the web UI strings to i18n

* update translations for more coverage

* remove duplicate logic/definitions

* fix android font family

* add shared reading setting hook between web and mobile

* unify reader settings context for both web and mobile

* remove unused export

* address coderabbit suggestions

* fix tests

2 files changed, 69 insertions, 0 deletions

diff --git a/packages/shared/types/readers.ts b/packages/shared/types/readers.ts
new file mode 100644
index 00000000..117dd51b
--- /dev/null
+++ b/packages/shared/types/readers.ts
@@ -0,0 +1,59 @@
+import { z } from "zod";
+
+import { ZReaderFontFamily, zReaderFontFamilySchema } from "./users";
+
+export const READER_DEFAULTS = {
+  fontSize: 18,
+  lineHeight: 1.6,
+  fontFamily: "serif" as const,
+} as const;
+
+export const READER_FONT_FAMILIES: Record<ZReaderFontFamily, string> = {
+  serif: "ui-serif, Georgia, Cambria, serif",
+  sans: "ui-sans-serif, system-ui, sans-serif",
+  mono: "ui-monospace, Menlo, Monaco, monospace",
+} as const;
+
+// Setting constraints for UI controls
+export const READER_SETTING_CONSTRAINTS = {
+  fontSize: { min: 12, max: 24, step: 1 },
+  lineHeight: { min: 1.2, max: 2.5, step: 0.1 },
+} as const;
+
+// Formatting functions for display
+export function formatFontSize(value: number): string {
+  return `${value}px`;
+}
+
+export function formatLineHeight(value: number): string {
+  return value.toFixed(1);
+}
+
+export function formatFontFamily(
+  value: ZReaderFontFamily,
+  t?: (key: string) => string,
+): string {
+  if (t) {
+    return t(`settings.info.reader_settings.${value}`);
+  }
+  // Fallback labels when no translation function provided
+  switch (value) {
+    case "serif":
+      return "Serif";
+    case "sans":
+      return "Sans Serif";
+    case "mono":
+      return "Monospace";
+  }
+}
+
+export const zReaderSettings = z.object({
+  fontSize: z.number().int().min(12).max(24),
+  lineHeight: z.number().min(1.2).max(2.5),
+  fontFamily: zReaderFontFamilySchema,
+});
+
+export type ReaderSettings = z.infer<typeof zReaderSettings>;
+
+export const zReaderSettingsPartial = zReaderSettings.partial();
+export type ReaderSettingsPartial = z.infer<typeof zReaderSettingsPartial>;
diff --git a/packages/shared/types/users.ts b/packages/shared/types/users.ts
index 9f020d52..73b99885 100644
--- a/packages/shared/types/users.ts
+++ b/packages/shared/types/users.ts
@@ -102,6 +102,9 @@ export const zUserStatsResponseSchema = z.object({
   ),
 });
 
+export const zReaderFontFamilySchema = z.enum(["serif", "sans", "mono"]);
+export type ZReaderFontFamily = z.infer<typeof zReaderFontFamilySchema>;
+
 export const zUserSettingsSchema = z.object({
   bookmarkClickAction: z.enum([
     "open_original_link",
@@ -112,6 +115,10 @@ export const zUserSettingsSchema = z.object({
   backupsEnabled: z.boolean(),
   backupsFrequency: z.enum(["daily", "weekly"]),
   backupsRetentionDays: z.number().int().min(1).max(365),
+  // Reader settings (nullable = opt-in, null means use client default)
+  readerFontSize: z.number().int().min(12).max(24).nullable(),
+  readerLineHeight: z.number().min(1.2).max(2.5).nullable(),
+  readerFontFamily: zReaderFontFamilySchema.nullable(),
 });
 
 export type ZUserSettings = z.infer<typeof zUserSettingsSchema>;
@@ -123,6 +130,9 @@ export const zUpdateUserSettingsSchema = zUserSettingsSchema.partial().pick({
   backupsEnabled: true,
   backupsFrequency: true,
   backupsRetentionDays: true,
+  readerFontSize: true,
+  readerLineHeight: true,
+  readerFontFamily: true,
 });
 
 export const zUpdateBackupSettingsSchema = zUpdateUserSettingsSchema.pick({