Say just which entries after the last message a handoff had no room for

CHANGELOG.md

@@ -12,6 +12,11 @@
   `sessions read` showed one entry with its tool output cut at 2,000
   characters, not at 40,000 as with `--count 1`. `read_session` now takes a
   `count` of 0 as 1.
+- **Handoff:** "Where it stopped" says which entries after the agent's
+  last message it had no room for when none of them fit. It said nothing
+  of them. The entries it says it left out for room no longer start or
+  end with a system note, which a handoff always leaves out, so a note
+  alone is no longer said to be left out for room.
 - **`status`, `check_limits` and `doctor`** say why an account can't be
   read in the same words. `check_limits`' verdict on the first account
   says how to fix it, as the others do, not only that its limits can't be

src/sessions/handoff.rs

@@ -466,7 +466,7 @@ fn stopped(entries: &[Entry], stop: usize, quoted: &[usize], share: usize, now:
         ..SAID
     };
     let first = render(stop, last, &opening, now);
-    let (after, _) = fit(
+    let (after, full) = fit(
         stop + 1..entries.len(),
         share.saturating_sub(first.len()),
         |at| {
@@ -483,11 +483,13 @@ fn stopped(entries: &[Entry], stop: usize, quoted: &[usize], share: usize, now:
             })
         },
     );
-    let from = after.first().map_or(entries.len(), |(at, _)| *at);
-    let gap = match from > stop + 1 && from < entries.len() {
-        true => format!("\n\n{}", left_out(stop + 1, from - 1)),
-        false => String::new(),
-    };
+    // A system note is left out wherever it falls, not for room.
+    let gap = full
+        .and_then(|at| {
+            let from = (stop + 1..=at).find(|&next| entries[next].kind != Kind::System)?;
+            Some(format!("\n\n{}", left_out(from, at)))
+        })
+        .unwrap_or_default();
     let what = match (last.kind, entries.len() - stop - 1) {
         (Kind::Assistant, 0) => "Its last message, the session's last entry.".to_owned(),
         (Kind::Assistant, count) => format!(
@@ -995,6 +997,57 @@ mod tests {
         );
     }
 
+    /// Where it stopped says which entries after the last message it had no
+    /// room for: from the first after it that isn't a system note to the one
+    /// that didn't fit.
+    #[test]
+    fn where_it_stopped_says_just_what_it_left_out_for_room() {
+        let failed = "test quoted_commas ... FAILED\n";
+        let tests = |output: &str| {
+            call(
+                "Bash",
+                r#"{"command": "cargo test"}"#,
+                output,
+                true,
+                Role::Work,
+            )
+        };
+        let stop = |after: Vec<Entry>| {
+            let mut entries = vec![
+                said(Kind::User, 0, "Fix the CSV parser."),
+                said(Kind::Assistant, 1, "Running the tests."),
+            ];
+            entries.extend(after);
+            stopped(&entries, 1, &[], 1000, 10 * MINUTE)
+        };
+        // A system note is left out wherever it falls, not for room.
+        let noted = stop(vec![said(Kind::System, 2, "A reminder."), tests(failed)]);
+        assert!(!noted.contains("left out for room"), "{noted}");
+        // Room ran out at #2; the note after it doesn't count with it.
+        let cut = stop(vec![
+            tests(&failed.repeat(60)),
+            said(Kind::System, 3, "A reminder."),
+            tests(failed),
+        ]);
+        assert!(cut.contains("\nEntry #2 is left out for room.\n"), "{cut}");
+        // Nor does the note before it.
+        let noted_first = stop(vec![
+            said(Kind::System, 2, "A reminder."),
+            tests(&failed.repeat(60)),
+            tests(failed),
+        ]);
+        assert!(
+            noted_first.contains("\nEntry #3 is left out for room.\n"),
+            "{noted_first}"
+        );
+        // With room for none of the entries after the last message.
+        let none = stop(vec![tests(&failed.repeat(60))]);
+        assert!(
+            none.contains("\nEntry #2 is left out for room.\n"),
+            "{none}"
+        );
+    }
+
     #[test]
     fn a_request_answered_is_kept_though_the_next_starts_the_same() {
         let first = "Run the tests and fix the failures in the parser crate.";