diff --git a/desktop/src/lib/handlePreviewLink.test.ts b/desktop/src/lib/handlePreviewLink.test.ts
new file mode 100644
index 00000000..a1ed84a6
--- /dev/null
+++ b/desktop/src/lib/handlePreviewLink.test.ts
@@ -0,0 +1,66 @@
+import { describe, expect, it, vi } from 'vitest'
+import { handlePreviewLink, type PreviewLinkDeps } from './handlePreviewLink'
+
+function makeDeps(overrides?: Partial<PreviewLinkDeps>): PreviewLinkDeps {
+  return {
+    sessionId: 's1',
+    serverBaseUrl: 'http://127.0.0.1:8787',
+    openBrowser: vi.fn(),
+    openFilePreview: vi.fn(),
+    openExternal: vi.fn(),
+    ...overrides,
+  }
+}
+
+describe('handlePreviewLink', () => {
+  it('routes loopback urls to openBrowser with the url', () => {
+    const deps = makeDeps()
+    const handled = handlePreviewLink('http://localhost:5173/', deps)
+    expect(handled).toBe(true)
+    expect(deps.openBrowser).toHaveBeenCalledWith('s1', 'http://localhost:5173/')
+    expect(deps.openFilePreview).not.toHaveBeenCalled()
+    expect(deps.openExternal).not.toHaveBeenCalled()
+  })
+
+  it('routes absolute html file paths to openBrowser with the preview-fs url', () => {
+    const deps = makeDeps()
+    const handled = handlePreviewLink('/Users/x/index.html', deps)
+    expect(handled).toBe(true)
+    // previewFsUrl preserves the leading slash, yielding an intentional `//`
+    // between <sessionId> and the absolute path so the server resolves it as
+    // an absolute-within-workspace path.
+    expect(deps.openBrowser).toHaveBeenCalledWith(
+      's1',
+      'http://127.0.0.1:8787/preview-fs/s1//Users/x/index.html',
+    )
+    expect(deps.openFilePreview).not.toHaveBeenCalled()
+    expect(deps.openExternal).not.toHaveBeenCalled()
+  })
+
+  it('routes relative previewable docs to openFilePreview with the relative path', () => {
+    const deps = makeDeps()
+    const handled = handlePreviewLink('docs/report.md', deps)
+    expect(handled).toBe(true)
+    expect(deps.openFilePreview).toHaveBeenCalledWith('s1', 'docs/report.md')
+    expect(deps.openBrowser).not.toHaveBeenCalled()
+    expect(deps.openExternal).not.toHaveBeenCalled()
+  })
+
+  it('routes remote http(s) to openExternal with the url', () => {
+    const deps = makeDeps()
+    const handled = handlePreviewLink('https://example.com/', deps)
+    expect(handled).toBe(true)
+    expect(deps.openExternal).toHaveBeenCalledWith('https://example.com/')
+    expect(deps.openBrowser).not.toHaveBeenCalled()
+    expect(deps.openFilePreview).not.toHaveBeenCalled()
+  })
+
+  it('returns false for ignored links and calls no deps', () => {
+    const deps = makeDeps()
+    const handled = handlePreviewLink('#x', deps)
+    expect(handled).toBe(false)
+    expect(deps.openBrowser).not.toHaveBeenCalled()
+    expect(deps.openFilePreview).not.toHaveBeenCalled()
+    expect(deps.openExternal).not.toHaveBeenCalled()
+  })
+})
diff --git a/desktop/src/lib/handlePreviewLink.ts b/desktop/src/lib/handlePreviewLink.ts
new file mode 100644
index 00000000..57e5d164
--- /dev/null
+++ b/desktop/src/lib/handlePreviewLink.ts
@@ -0,0 +1,43 @@
+import { classifyPreviewLink } from './previewLinkRouter'
+
+export type PreviewLinkDeps = {
+  sessionId: string
+  serverBaseUrl: string
+  openBrowser: (sessionId: string, url: string) => void
+  openFilePreview: (sessionId: string, path: string) => void
+  openExternal: (url: string) => void
+}
+
+/**
+ * Build a `/preview-fs/<sessionId>/<path>` URL for the local server.
+ *
+ * Absolute file paths (leading slash) are preserved as-is, so the resulting URL
+ * carries a `//` between `<sessionId>` and the path. That double slash is
+ * intentional: the server slices everything after the `<sessionId>` segment and
+ * runs `path.resolve(workDir, relPath)`, so an absolute path is resolved as an
+ * absolute-within-workspace path and sandbox-checked against the work dir root.
+ */
+function previewFsUrl(base: string, sessionId: string, filePath: string): string {
+  return `${base.replace(/\/$/, '')}/preview-fs/${encodeURIComponent(sessionId)}/${filePath.replace(/^\/+/, '/')}`
+}
+
+/** Returns true if handled (caller should preventDefault). */
+export function handlePreviewLink(href: string, deps: PreviewLinkDeps): boolean {
+  const cls = classifyPreviewLink(href)
+  switch (cls.kind) {
+    case 'browser-localhost':
+      deps.openBrowser(deps.sessionId, cls.url!)
+      return true
+    case 'browser-file':
+      deps.openBrowser(deps.sessionId, previewFsUrl(deps.serverBaseUrl, deps.sessionId, cls.path!))
+      return true
+    case 'file-preview':
+      deps.openFilePreview(deps.sessionId, cls.path!)
+      return true
+    case 'remote':
+      deps.openExternal(cls.url!)
+      return true
+    default:
+      return false
+  }
+}