fix: hopefully fixed the background task progress situation

specs/generation.allium

@@ -44,6 +44,10 @@ surface GenerationRuntimeSurface {
         -- "Generated" for a full render and "Rewrote" for a validation apply —
         -- and advances the bar by the number of URLs written.
         --
+        -- Before section work begins, generation counts its planned URLs. The
+        -- task reports 0/total immediately and advances once per rendered URL,
+        -- matching bDS2's route-based generation progress.
+        --
         -- Full generation and validation apply share the same structuring: a
         -- task group containing one task per section (Render Site Core, Render
         -- Single Posts, Render Category Archives, Render Tag Archives, Render

specs/layout.allium

@@ -263,7 +263,8 @@ invariant PanelTabFallback {
 }
 
 -- Tasks tab: last 10 tasks, newest first, with progress/cancel.
---   Tasks with shared group_id are collapsible groups showing aggregate progress.
+--   Tasks with shared group_id are collapsible groups showing bDS2-style
+--   average child progress; pending children contribute zero.
 -- Output tab: log entries with copy-all button.
 --   The panel opens on Output automatically when a blogmark transform fails
 --   or a transform script writes output.

specs/task.allium

@@ -116,6 +116,11 @@ invariant ProgressThrottled {
     -- At most one progress event per 250ms per task
 }
 
+invariant GroupProgressAggregatesChildren {
+    -- Matches bDS2: group progress averages every child task contribution.
+    -- Pending tasks contribute 0 and completed tasks contribute 1.
+}
+
 invariant FinishedTaskRetention {
     -- The status snapshot surfaces only the most recent finished tasks:
     -- completed/failed/cancelled tasks beyond config.recent_finished_limit