CB-WP-0035: a session that answers nothing

Two reports, one cause: the script's fetch had no .catch. When the server
had exited the promise rejected, the chain never ran, and not even the
status line moved — so a dead server and a click that did nothing were
indistinguishable. play again read as a dead button, and the linger
timeout was invisible.

Now a rejection says the session is gone and seals the page, and a
5-second heartbeat against a new /alive notices it without needing a
click, which is what the timeout case requires. The beat carries the
token, and does not extend the linger: that deadline is absolute.

The harness had the same hole. jsrun's fetch stub had no .catch, so the
branch that notices a dead server would have been unreachable in every
test — the very defect the stub's own comment records from CB-WP-0024.
Teaching it __failing, .catch and a recorded setInterval was the fix;
writing the script defensively would have repeated the trap.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/cb-render-html/src/lib.rs

@@ -52,6 +52,7 @@ pub use doc::{document, text_of, Endpoints};
 /// The endpoint pair every test in this crate posts to.
 #[cfg(test)]
 const TEST_ENDPOINTS: Endpoints<'static> = Endpoints {
+    alive: "/alive?t=x",
     command: "/command?t=x",
     note: "/note?t=x",
 };
@@ -608,6 +609,84 @@ mod gamelog {
         }
     }
 
+    /// CB-WP-0035. A server that has gone must be NOTICED.
+    ///
+    /// The script's `fetch` had no rejection handler, so when the process
+    /// had exited the promise rejected and the chain never ran — not even
+    /// the status line moved. Reported twice: *"play again does not
+    /// report that the session is no longer available"*, and the linger
+    /// timeout going unnoticed.
+    ///
+    /// **Both from one cause**, so both are asserted: the click path and
+    /// the heartbeat that needs no click.
+    #[test]
+    fn a_session_that_answers_nothing_is_reported_and_sealed() {
+        let page = crate::doc::ending(
+            None,
+            "the game ended",
+            "/command?t=x",
+            None,
+            "/alive?t=x",
+            crate::doc::Account::of(&[]),
+            &[],
+        );
+        for (beat, what) in [(false, "pressing a control"), (true, "the heartbeat")] {
+            let (live, status) = crate::jsrun::unanswered(&page, beat).expect("run the page");
+            assert!(
+                status.contains("no longer available"),
+                "{what} said nothing about the session: {status:?}"
+            );
+            assert!(
+                status.contains("[sealed]"),
+                "{what} left the page looking live: {status:?}"
+            );
+            assert!(
+                live.is_empty(),
+                "{what} left {live:?} still droppable on a dead session"
+            );
+        }
+    }
+
+    /// **Both** pages must carry the heartbeat (CB-WP-0035).
+    ///
+    /// The first cut wired it into the ending page only, and the gate
+    /// caught it as an unused variable — which is luck, not a control.
+    /// The timeout matters MOST during play: that is when a player walks
+    /// away, and the table is the thing that must stop looking live.
+    #[test]
+    fn every_page_can_tell_the_session_has_gone() {
+        let playing = document_with_log(
+            &crate::testfix::view(Some(PlayerId(0))),
+            &[],
+            crate::TEST_ENDPOINTS,
+            Some(PlayerId(0)),
+            false,
+            Account::of(&[]),
+            &[],
+        );
+        let ended = crate::doc::ending(
+            None,
+            "m",
+            "/command?t=x",
+            None,
+            "/alive?t=x",
+            crate::doc::Account::of(&[]),
+            &[],
+        );
+        for (name, page) in [("the table", &playing), ("the ending page", &ended)] {
+            assert!(
+                page.contains("CB_ALIVE"),
+                "{name} cannot notice the session ending"
+            );
+            // With the token: an unauthenticated heartbeat is refused,
+            // and a refusal every 5s would seal a LIVE session.
+            assert!(
+                page.contains("/alive?t="),
+                "{name}'s heartbeat carries no token"
+            );
+        }
+    }
+
     /// CB-WP-0034. The move button must name **who**.
     ///
     /// Reported three times across three sessions, two days apart, and it
@@ -1618,6 +1697,7 @@ mod ending_page {
             "the game ended",
             "/command?t=x",
             None,
+            "/alive?t=x",
             crate::doc::Account::of(&[]),
             &[],
         )
@@ -1704,6 +1784,7 @@ mod ending_page {
                 "m",
                 "/command?t=x",
                 None,
+                "/alive?t=x",
                 crate::doc::Account::of(&[]),
                 &[],
             ),
@@ -1762,6 +1843,7 @@ mod ending_page {
                 "m",
                 "/command?t=x",
                 None,
+                "/alive?t=x",
                 crate::doc::Account::of(&[]),
                 &[],
             ))
@@ -1786,6 +1868,7 @@ mod ending_page {
             "P1 ran out of input",
             "/command?t=x",
             None,
+            "/alive?t=x",
             crate::doc::Account::of(&[]),
             &[],
         ));
@@ -1805,6 +1888,7 @@ mod ending_page {
             "m",
             "/command?t=x",
             None,
+            "/alive?t=x",
             crate::doc::Account::of(&[]),
             &[],
         ));
@@ -1835,6 +1919,7 @@ mod ending_page {
             "m",
             "/command?t=x",
             None,
+            "/alive?t=x",
             crate::doc::Account::of(&[]),
             &[],
         ));