Point the unreachable-relay advice at the next session, not this app

app/src/terminal/socket-url.test.ts

@@ -84,6 +84,27 @@ describe("a session on a relay the app cannot reach", () => {
     }
   });
 
+  it("offers the relay setting for the next session, not as a way back into this one", () => {
+    /*
+     * SHELL_ONLINE_SERVER belongs to the CLI that starts a session, not to
+     * this app, which reads VITE_RELAY_URL. Told to "start it" in a sentence
+     * whose subject was the app, people set the variable here and nothing
+     * changed -- and a session that has already finished cannot be reopened
+     * by starting anything. The advice is about the next session.
+     */
+    const result = resolveSessionSocket(
+      `https://shell.online/s/${ID}`,
+      "http://localhost:5173",
+      RELAY,
+    );
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.reason).not.toContain("Start it with");
+      expect(result.reason).not.toContain("to open it here");
+      expect(result.reason).toContain("A session started with");
+    }
+  });
+
   it("explains when no relay is configured at all", () => {
     const result = resolveSessionSocket(
       `https://shell.online/s/${ID}`,

app/src/terminal/socket-url.ts

@@ -76,8 +76,9 @@ export function resolveSessionSocket(
     return {
       ok: false,
       reason:
-        `This session is on ${share.origin}, but this app proxies to ${relay.origin}. ` +
-        `Start it with SHELL_ONLINE_SERVER=${relay.origin} to open it here.`,
+        `This session is on ${share.origin}, but this app reaches ${relay.origin}, ` +
+        `so its screen is only available where it was started. ` +
+        `A session started with SHELL_ONLINE_SERVER=${relay.origin} opens here.`,
     };
   }