test(web,contracts): cover ChatFontSize schema + timeline CSS var wiring

Two focused additions guarding the chat font-size feature:

- `packages/contracts/src/settings.test.ts` — new file, 11 tests.
  Covers `ChatFontSize` schema bounds (min 12 / max 24, rejects below,
  above, non-integer, non-numeric), `ClientSettingsSchema` decoding
  default behaviour for `chatFontSize`, and confirms both
  `DEFAULT_CLIENT_SETTINGS` and `DEFAULT_UNIFIED_SETTINGS` carry the
  default value 14.
- `apps/web/src/components/chat/MessagesTimeline.test.tsx` — one new
  SSR-render test asserting that a `chatFontSize={20}` prop surfaces as
  `--chat-font-size:20px` on the list wrapper, pinning the contract
  between the prop and the CSS variable that drives every `text-chat-*`
  tier plus `.chat-markdown` scaling.

Author: akarabach

apps/web/src/components/chat/MessagesTimeline.test.tsx

@@ -161,6 +161,32 @@ describe("MessagesTimeline", () => {
     expect(markup).toContain("Work log");
   });
 
+  it("propagates chatFontSize as the --chat-font-size CSS variable on the list wrapper", async () => {
+    const { MessagesTimeline } = await import("./MessagesTimeline");
+    const markup = renderToStaticMarkup(
+      <MessagesTimeline
+        {...buildProps()}
+        chatFontSize={20}
+        timelineEntries={[
+          {
+            id: "entry-1",
+            kind: "message",
+            createdAt: "2026-03-17T19:12:28.000Z",
+            message: {
+              id: MessageId.make("message-1"),
+              role: "user",
+              text: "hi",
+              createdAt: "2026-03-17T19:12:28.000Z",
+              streaming: false,
+            },
+          },
+        ]}
+      />,
+    );
+
+    expect(markup).toContain("--chat-font-size:20px");
+  });
+
   it("formats changed file paths from the workspace root", async () => {
     const { MessagesTimeline } = await import("./MessagesTimeline");
     const markup = renderToStaticMarkup(

packages/contracts/src/settings.test.ts

@@ -0,0 +1,72 @@
+import { describe, expect, it } from "vitest";
+import { Schema } from "effect";
+
+import {
+  ChatFontSize,
+  CHAT_FONT_SIZE_MAX,
+  CHAT_FONT_SIZE_MIN,
+  ClientSettingsSchema,
+  DEFAULT_CHAT_FONT_SIZE,
+  DEFAULT_CLIENT_SETTINGS,
+  DEFAULT_UNIFIED_SETTINGS,
+} from "./settings.ts";
+
+const decodeChatFontSize = Schema.decodeUnknownSync(ChatFontSize);
+const decodeClientSettings = Schema.decodeUnknownSync(ClientSettingsSchema);
+
+describe("ChatFontSize schema", () => {
+  it("exposes the expected bounds and default", () => {
+    expect(CHAT_FONT_SIZE_MIN).toBe(12);
+    expect(CHAT_FONT_SIZE_MAX).toBe(24);
+    expect(DEFAULT_CHAT_FONT_SIZE).toBe(14);
+  });
+
+  it("accepts the default, min and max values", () => {
+    expect(decodeChatFontSize(DEFAULT_CHAT_FONT_SIZE)).toBe(DEFAULT_CHAT_FONT_SIZE);
+    expect(decodeChatFontSize(CHAT_FONT_SIZE_MIN)).toBe(CHAT_FONT_SIZE_MIN);
+    expect(decodeChatFontSize(CHAT_FONT_SIZE_MAX)).toBe(CHAT_FONT_SIZE_MAX);
+  });
+
+  it("rejects values below the minimum", () => {
+    expect(() => decodeChatFontSize(CHAT_FONT_SIZE_MIN - 1)).toThrow();
+  });
+
+  it("rejects values above the maximum", () => {
+    expect(() => decodeChatFontSize(CHAT_FONT_SIZE_MAX + 1)).toThrow();
+  });
+
+  it("rejects non-integer values", () => {
+    expect(() => decodeChatFontSize(14.5)).toThrow();
+  });
+
+  it("rejects non-numeric values", () => {
+    expect(() => decodeChatFontSize("14")).toThrow();
+    expect(() => decodeChatFontSize(null)).toThrow();
+  });
+});
+
+describe("ClientSettingsSchema chatFontSize decoding default", () => {
+  it("fills in the default when chatFontSize is omitted from the input", () => {
+    const parsed = decodeClientSettings({});
+    expect(parsed.chatFontSize).toBe(DEFAULT_CHAT_FONT_SIZE);
+  });
+
+  it("preserves a provided chatFontSize inside the valid range", () => {
+    const parsed = decodeClientSettings({ chatFontSize: 20 });
+    expect(parsed.chatFontSize).toBe(20);
+  });
+
+  it("rejects a chatFontSize outside the valid range", () => {
+    expect(() => decodeClientSettings({ chatFontSize: 100 })).toThrow();
+  });
+});
+
+describe("Default settings objects expose chatFontSize", () => {
+  it("DEFAULT_CLIENT_SETTINGS carries the default chat font size", () => {
+    expect(DEFAULT_CLIENT_SETTINGS.chatFontSize).toBe(DEFAULT_CHAT_FONT_SIZE);
+  });
+
+  it("DEFAULT_UNIFIED_SETTINGS carries the default chat font size", () => {
+    expect(DEFAULT_UNIFIED_SETTINGS.chatFontSize).toBe(DEFAULT_CHAT_FONT_SIZE);
+  });
+});