feat(plugins): add theme contributions

Adds plugin-contributed light and dark app themes, including persistence, host-aware coalescing, fallback behavior, documentation, examples, and browser/iOS QA.

packages/protocol/src/messages.plugins.test.ts

@@ -115,6 +115,28 @@ describe("plugin protocol compatibility", () => {
     expect(current.payload.features?.pluginLogs).toBe(true);
   });
 
+  it("keeps the plugin themes capability optional for older server info", () => {
+    const older = StatusMessageSchema.parse({
+      type: "status",
+      payload: {
+        status: "server_info",
+        serverId: "older-host",
+        features: { plugins: true },
+      },
+    });
+    const current = StatusMessageSchema.parse({
+      type: "status",
+      payload: {
+        status: "server_info",
+        serverId: "current-host",
+        features: { plugins: true, pluginThemes: true },
+      },
+    });
+
+    expect(older.payload.features?.pluginThemes).toBeUndefined();
+    expect(current.payload.features?.pluginThemes).toBe(true);
+  });
+
   it("keeps the catalog change notification safe for older clients", () => {
     expect(
       StatusMessageSchema.parse({

packages/protocol/src/messages.ts

@@ -3324,6 +3324,10 @@ export const ServerInfoStatusPayloadSchema = z
         pluginManagement: z.boolean().optional(),
         // COMPAT(pluginLogs): added in v0.4.0, remove gate after 2027-08-16.
         pluginLogs: z.boolean().optional(),
+        // COMPAT(pluginThemes): added in v0.5.0, remove gate after 2027-08-20.
+        // A daemon that predates this flag keeps `addTheme` in the server bundle it compiles,
+        // so a theme plugin cannot start there at all.
+        pluginThemes: z.boolean().optional(),
         // COMPAT(skillManagement): added in v0.4.0, remove gate after 2027-08-16.
         skillManagement: z.boolean().optional(),
         // COMPAT(terminalRestoreModes): added in v0.1.81, remove gate after 2026-11-23.