feat(app): improve desktop multi-server support (#30678)

Co-authored-by: Brendan Allan <git@brendonovich.dev>

packages/app/src/utils/server-scope.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, test } from "bun:test"
+import { ScopedKey, ServerScope, SessionRouteKey, SessionStateKey, migrateLegacySessionStateKeys } from "./server-scope"
+
+describe("ServerScope", () => {
+  test("uses a stable local scope for the canonical sidecar", () => {
+    expect(String(ServerScope.fromServerKey("sidecar" as Parameters<typeof ServerScope.fromServerKey>[0]))).toBe("local")
+  })
+
+  test("keeps configured loopback servers distinct from the canonical sidecar", () => {
+    expect(String(ServerScope.fromServerKey("http://localhost:4096" as Parameters<typeof ServerScope.fromServerKey>[0]))).toBe(
+      "http://localhost:4096",
+    )
+  })
+
+  test("uses a stable local scope for an explicit canonical web server", () => {
+    const key = "http://localhost:4096" as Parameters<typeof ServerScope.fromServerKey>[0]
+    expect(String(ServerScope.fromServerKey(key, key))).toBe("local")
+  })
+})
+
+describe("SessionStateKey", () => {
+  test("combines local and remote scope with route identity", () => {
+    const route = SessionRouteKey.fromRoute("cmVwbw", "session-1")
+    expect(String(SessionStateKey.from(ServerScope.local, route))).toBe("local\0cmVwbw/session-1")
+    expect(String(SessionStateKey.from("https://windows.example" as ServerScope, route))).toBe(
+      "https://windows.example\0cmVwbw/session-1",
+    )
+    expect(SessionStateKey.from("https://debian.example" as ServerScope, route)).not.toBe(
+      SessionStateKey.from("https://windows.example" as ServerScope, route),
+    )
+  })
+
+  test("extracts route keys from scoped and legacy state keys", () => {
+    expect(String(SessionStateKey.route("cmVwbw/session-1"))).toBe("cmVwbw/session-1")
+    expect(String(SessionStateKey.route("local\0cmVwbw/session-1"))).toBe("cmVwbw/session-1")
+    expect(String(SessionStateKey.route("https://debian.example\0cmVwbw/session-1"))).toBe("cmVwbw/session-1")
+  })
+})
+
+describe("migrateLegacySessionStateKeys", () => {
+  test("copies legacy route keys into local scope without overwriting scoped state", () => {
+    expect(
+      migrateLegacySessionStateKeys({
+        "cmVwbw/session-1": { active: "legacy" },
+        "local\0cmVwbw/session-1": { active: "scoped" },
+        "https://debian.example\0cmVwbw/session-1": { active: "remote" },
+      }),
+    ).toEqual({
+      "local\0cmVwbw/session-1": { active: "scoped" },
+      "https://debian.example\0cmVwbw/session-1": { active: "remote" },
+    })
+  })
+
+  test("rejects invalid identity fragments", () => {
+    expect(() => ScopedKey.from(ServerScope.local, "bad\0directory")).toThrow("Scoped key part cannot contain null bytes")
+  })
+})