session groups: list each pane once, save each group once

a pane in several sessions (a session group, `new-session -t`, or a
linked window) was listed once per session: every agent of a group showed
twice in the menu, panel, search, `dingger status`, and the counts. and
snapshots saved each session of a group with its own copy of the windows,
so restore would have rebuilt them twice and resumed each agent twice on
one session file.

- a pane keeps its first listing (tmux lists sessions by name) and is
  attended if the user looks at it through any session of the group.
- snapshots keep the first session of each group; the others are not
  restored.

e2e step 19 covers both; the previous binaries fail it. two checks (step
11's and this one) waited for idle after a turn that started from idle,
which passed before the turn was even processed: they now wait for
working first, and the negative control for group attendance fails as it
should. step 18 now waits for the snapshot it later restores from.

1 files changed, 10 insertions, 1 deletions

diff --git a/crates/dinggerd/src/snapshot.rs b/crates/dinggerd/src/snapshot.rs
index d4ee321..715bf37 100644
--- a/crates/dinggerd/src/snapshot.rs
+++ b/crates/dinggerd/src/snapshot.rs
@@ -197,13 +197,22 @@ pub fn capture(now_ms: u64) -> Option<Snapshot> {
         "#{@agent_session}",
         "#{@dingger_cmd}",
         "#{pane_dead}",
+        "#{?session_grouped,#{session_group},}",
     ]
     .join("\t");
     let out = tmux::run(&["list-panes", "-a", "-F", &format]).ok()?;
     let lines: Vec<Vec<&str>> = out
         .lines()
         .map(|line| line.split('\t').collect::<Vec<_>>())
-        .filter(|f| f.len() >= 21)
+        .filter(|f| f.len() >= 22)
+        .collect();
+    // One session per group: the others show the same windows, and saving
+    // them would restore every window, and resume every agent, twice. The
+    // first listed (tmux lists sessions by name) stands for its group.
+    let mut group_of_kept: std::collections::HashMap<&str, &str> = std::collections::HashMap::new();
+    let lines: Vec<Vec<&str>> = lines
+        .into_iter()
+        .filter(|f| f[21].is_empty() || *group_of_kept.entry(f[21]).or_insert(f[0]) == f[0])
         .collect();
     // What runs in the foreground of each pane's terminal.
     let pane_pids: Vec<u32> = lines