[feat](trx-frontend-http): add interleave time for overlapping TimeSpan entries

When multiple time-span entries are active simultaneously, the scheduler
now cycles through them by slot: slot = floor(utc_min / interleave_min) % count.
The interleave_min field is optional (null disables, first match wins).

UI: "Interleave time (min)" number input in the TimeSpan section with a
hint explaining the behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -716,6 +716,12 @@
         <!-- Time Span section -->
         <div id="scheduler-timespan-section" class="sch-section" style="display:none;">
           <div class="sch-section-title">Time Span Entries (UTC)</div>
+          <div class="sch-row" style="margin-bottom:0.75rem;">
+            <label class="sch-label">Interleave time (min)
+              <input type="number" id="scheduler-ts-interleave" class="status-input" min="1" max="60" placeholder="off" style="width:7rem;" />
+            </label>
+            <small style="color:var(--text-muted);align-self:flex-end;padding-bottom:0.35rem;">When multiple entries overlap, spend this many minutes at each before cycling. Leave blank to disable.</small>
+          </div>
           <table class="sch-ts-table">
             <thead>
               <tr><th>Start</th><th>End</th><th>Bookmark</th><th>Label</th><th></th></tr>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/scheduler.js

@@ -195,6 +195,13 @@
       renderBookmarkSelect("scheduler-gl-night", null);
     }
 
+    // Interleave input
+    const ilEl = document.getElementById("scheduler-ts-interleave");
+    if (ilEl) {
+      const il = currentConfig && currentConfig.interleave_min;
+      ilEl.value = il ? il : "";
+    }
+
     // TimeSpan entries
     renderTimespanEntries();
 
@@ -374,6 +381,8 @@
     } else if (mode === "time_span") {
       config.entries =
         currentConfig && currentConfig.entries ? currentConfig.entries : [];
+      const ilVal = parseInt(document.getElementById("scheduler-ts-interleave").value, 10);
+      config.interleave_min = isNaN(ilVal) || ilVal <= 0 ? null : ilVal;
     }
 
     const btn = document.getElementById("scheduler-save-btn");

src/trx-client/trx-frontend/trx-frontend-http/src/scheduler.rs

@@ -78,6 +78,11 @@ pub struct SchedulerConfig {
     pub grayline: Option<GraylineConfig>,
     #[serde(default)]
     pub entries: Vec<ScheduleEntry>,
+    /// When multiple entries are active simultaneously, cycle through them,
+    /// spending this many minutes at each before advancing to the next.
+    /// `None` (or 0) disables interleaving — the first matching entry wins.
+    #[serde(default)]
+    pub interleave_min: Option<u32>,
 }
 
 // ============================================================================
@@ -265,21 +270,41 @@ fn grayline_bookmark_id(gl: &GraylineConfig, now_min: f64) -> Option<String> {
     }
 }
 
-fn timespan_bookmark_id(entries: &[ScheduleEntry], now_min: f64) -> Option<String> {
-    for entry in entries {
+fn entry_is_active(entry: &ScheduleEntry, now_min: f64) -> bool {
     let start = entry.start_min as f64;
     let end = entry.end_min as f64;
-        let in_window = if start <= end {
+    if start <= end {
         now_min >= start && now_min < end
     } else {
         // Spans midnight.
         now_min >= start || now_min < end
-        };
-        if in_window {
-            return Some(entry.bookmark_id.clone());
     }
 }
-    None
+
+fn timespan_bookmark_id(
+    entries: &[ScheduleEntry],
+    now_min: f64,
+    interleave_min: Option<u32>,
+) -> Option<String> {
+    let active: Vec<&ScheduleEntry> = entries
+        .iter()
+        .filter(|e| entry_is_active(e, now_min))
+        .collect();
+
+    if active.is_empty() {
+        return None;
+    }
+
+    // With interleaving and more than one active entry, pick by time slot.
+    if active.len() > 1 {
+        if let Some(step) = interleave_min.filter(|&s| s > 0) {
+            let slot = (now_min as u64 / step as u64) as usize % active.len();
+            return Some(active[slot].bookmark_id.clone());
+        }
+    }
+
+    // Default: first matching entry wins.
+    Some(active[0].bookmark_id.clone())
 }
 
 /// Current UTC time as minutes since midnight.
@@ -346,7 +371,7 @@ pub fn spawn_scheduler_task(
                         .as_ref()
                         .and_then(|gl| grayline_bookmark_id(gl, now_min)),
                     SchedulerMode::TimeSpan => {
-                        timespan_bookmark_id(&config.entries, now_min)
+                        timespan_bookmark_id(&config.entries, now_min, config.interleave_min)
                     }
                 };
 
@@ -459,6 +484,7 @@ pub async fn get_scheduler(
         mode: SchedulerMode::Disabled,
         grayline: None,
         entries: vec![],
+        interleave_min: None,
     });
     HttpResponse::Ok().json(config)
 }