silently ignore captures without edit on restart

commands.lua

@@ -451,12 +451,36 @@ function run_command_with_args(cmd_with_args)
 end
 
 -- commands that create columns also need to be recreatable from a title
+-- I'm assuming that special columns have multiple words, and single-word
+-- columns are always filenames. pensieve.love won't ever create filenames
+-- containing spaces.
 function create_column(column_name)
   if file_exists(Directory..column_name) then
     local column = {name=column_name}
     local pane = load_pane(column_name)
     table.insert(column, pane)
     table.insert(Surface, column)
+  elseif not column_name:find(' ') then
+    -- File not found
+    --
+    -- It makes me nervous to silently drop errors, but at this point there's
+    -- really nothing actionable someone can do in response to an error.
+    --
+    -- Deeper issue: no way yet to communicate errors in the UI.
+    --
+    -- Philosophical question: what does crash-only mean if you ever run into
+    -- data loss? There's a hard tension between resilience and silent failures.
+    --
+    -- For now I'm going to rely on all my protections against data loss
+    -- elsewhere. Lines.love has never lost my data in several months of use.
+    --
+    -- While data loss seems unlikely, there _is_ a legitimate way you can end
+    -- up with a filename that doesn't exist: start a capture, then change
+    -- your mind and never type anything into it. It will continue to show as
+    -- a column on the surface, but there's no file backing it. You can still
+    -- edit it later and create a file for it. But if you just quit, the
+    -- column will silently disappear after restart.
+    print('file not found: '..column_name)
   else
     -- delegate to one of various helpers based on the column name
     local column = {name=column_name}