fix(liveshare-protocol): forward only real route segments

The carrier matched forwarded routes by substring, so /api/present.hostile and /x/open-in-app/apps-foo were posted to the owner as if they were the read routes. Match only where the route starts a path segment and ends at the pathname or a following slash, keeping the Relay base path prefix working; add hit, subpath, prefix-neighbour and query cases.

packages/experimental/liveshare-protocol/src/viewer-carrier.ts

@@ -135,17 +135,36 @@ export function installViewerCarrier(options: ViewerCarrierOptions): void {
    */
   const forwardedRoutes = ['/open-in-app/apps', '/api/present.host']
   /**
-   * Owner path one page request forwards, matched by suffix because the page URL carries the Relay's own
-   * base path in front of it.
+   * Offset at which `route` starts a path segment run, ignoring a Relay base path in front of it.
    * @param pathname - Resolved request pathname.
+   * @param route - Owner route to find.
+   * @returns The offset, or undefined when the route appears only inside a longer segment.
+   */
+  const segmentOffset = (pathname: string, route: string): number | undefined => {
+    let from = 0
+    for (;;) {
+      const at = pathname.indexOf(route, from)
+      if (at === -1) return undefined
+      // The route starts with '/', so its own slash is the segment boundary; only the tail decides
+      // whether a longer segment (e.g. `/api/present.hostile`) merely shares the prefix.
+      const next = pathname[at + route.length]
+      if (next === undefined || next === '/') return at
+      from = at + 1
+    }
+  }
+  /**
+   * Owner path one page request forwards, matched at path-segment boundaries because the page URL carries
+   * the Relay's own base path in front of it. Prefix-neighbouring paths such as `/api/present.hostile` or
+   * `/x/open-in-app/apps-foo` are not this route.
+   * @param pathname - Resolved request pathname (query and hash already excluded).
    * @param method - Request method, already upper-cased.
    * @returns The owner path to post, or undefined when this request is not one of the forwarded routes.
    */
   const forwardedRoute = (pathname: string, method: string): string | undefined => {
     if (method !== 'GET') return undefined
     for (const route of forwardedRoutes) {
-      const at = pathname.lastIndexOf(route)
-      if (at !== -1) return pathname.slice(at)
+      const at = segmentOffset(pathname, route)
+      if (at !== undefined) return pathname.slice(at)
     }
     return undefined
   }

packages/experimental/liveshare-protocol/tests/viewer-carrier.client.spec.ts

@@ -541,6 +541,29 @@ describe('viewer carrier forwarded page routes', () => {
     expect(posted[0]).toMatchObject({ op: 'call', path: '/open-in-app/apps' })
   })
 
+  it('forwards a route only when it starts a path segment', async () => {
+    const below = carrier(() => json({ apps: ['finder'] }))
+    expect(await (await globalThis.fetch('/relay/s/abc/open-in-app/apps/foo')).json()).toEqual({ apps: ['finder'] })
+    expect(below.posted[0]).toMatchObject({ op: 'call', path: '/open-in-app/apps/foo' })
+    const exact = carrier(() => json({ name: 'owner-host' }))
+    expect(await (await globalThis.fetch('/relay/s/abc/api/present.host')).json()).toEqual({ name: 'owner-host' })
+    expect(exact.posted[0]).toMatchObject({ op: 'call', path: '/api/present.host' })
+  })
+
+  it('does not forward a prefix neighbour of a forwarded route', async () => {
+    const direct = directFetch()
+    expect(await (await globalThis.fetch('/api/present.hostile')).text()).toBe('direct:/api/present.hostile')
+    expect(await (await globalThis.fetch('/x/open-in-app/apps-foo')).text()).toBe('direct:/x/open-in-app/apps-foo')
+    expect(await (await globalThis.fetch('/api/present.hostile?x=1')).text()).toBe('direct:/api/present.hostile?x=1')
+    expect(direct).toHaveBeenCalledTimes(3)
+  })
+
+  it('forwards a hit whose page URL carries a query without passing it to the owner', async () => {
+    const { posted } = carrier(() => json({ name: 'owner-host', available: true, fileManager: 'finder' }))
+    expect(await (await globalThis.fetch('/relay/s/abc/api/present.host?x=1#frag')).json()).toMatchObject({ name: 'owner-host' })
+    expect(posted[0]).toMatchObject({ op: 'call', path: '/api/present.host' })
+  })
+
   it('leaves every other request to the page\u2019s own fetch', async () => {
     const direct = directFetch()
     expect(await (await globalThis.fetch('health')).text()).toBe('direct:health')