test: cover post-merge gaps in utils, services, and hooks

Adds specs for the files added or modified in the recent merge that
weren't yet covered: oauthReturnPath, withATProtoImages, link,
displayLanguage, and the useGitHubContent / useImageUpload /
useNoteFreshness hooks. Locks in the new pullLatest contract
({raw, failureStatus}) and the fetchLatestSha branch semantics
(ok/unauthorized/offline).

src/utils/displayLanguage.spec.ts

@@ -0,0 +1,38 @@
+import { afterEach, describe, expect, it, vi } from "vitest"
+
+import { displayLanguage } from "./displayLanguage"
+
+describe("displayLanguage", () => {
+  afterEach(() => {
+    vi.restoreAllMocks()
+  })
+
+  it("returns null when no language code is given", () => {
+    expect(displayLanguage()).toBeNull()
+    expect(displayLanguage("")).toBeNull()
+  })
+
+  it("returns a human-readable name for a known language code", () => {
+    expect(displayLanguage("en")).toMatch(/^English/i)
+  })
+
+  it("works for French", () => {
+    expect(displayLanguage("fr")).toBeTruthy()
+  })
+
+  it("returns null and logs a warning when Intl.DisplayNames throws", () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {})
+    const original = Intl.DisplayNames
+    // Force the constructor to throw
+    ;(Intl as unknown as { DisplayNames: unknown }).DisplayNames = function () {
+      throw new Error("boom")
+    }
+
+    try {
+      expect(displayLanguage("en")).toBeNull()
+      expect(warn).toHaveBeenCalled()
+    } finally {
+      ;(Intl as unknown as { DisplayNames: unknown }).DisplayNames = original
+    }
+  })
+})

src/utils/link.spec.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest"
+
+import { isExternalLink } from "./link"
+
+describe("isExternalLink", () => {
+  const ORIGIN = window.location.origin
+
+  it("returns false for same-origin absolute URLs", () => {
+    expect(isExternalLink(`${ORIGIN}/alice/notes`)).toBe(false)
+  })
+
+  it("returns true for an https URL on a different origin", () => {
+    expect(isExternalLink("https://github.com/anywhere")).toBe(true)
+  })
+
+  it("returns true for an http URL on a different origin", () => {
+    expect(isExternalLink("http://example.com")).toBe(true)
+  })
+
+  it("returns false for relative paths (no http/https prefix)", () => {
+    expect(isExternalLink("/alice/notes")).toBe(false)
+    expect(isExternalLink("./neighbor.md")).toBe(false)
+  })
+
+  it("returns false for mailto and other non-http schemes", () => {
+    expect(isExternalLink("mailto:user@example.com")).toBe(false)
+    expect(isExternalLink("ftp://files.example.com")).toBe(false)
+  })
+
+  it("returns false for an https URL that happens to start with the origin", () => {
+    expect(isExternalLink(`${ORIGIN}/deep/path`)).toBe(false)
+  })
+})