fix(codecompanion): improve error handling for empty stderr output

- Enhanced flatten_table_to_string to filter out empty error messages
- Added logic to distinguish actual errors from empty stderr output
- Prevents false error reporting when VectorCode operations succeed but have no stderr
- Provides meaningful fallback error message for truly empty error conditions
- Fixes issue where successful operations with empty stderr were reported as { "" } errors

Resolves the confusing empty error message issue in CodeCompanion integration.

Author: ruslanfialkovskii

lua/vectorcode/integrations/codecompanion/common.lua

@@ -16,7 +16,18 @@ return {
     if type(t) == "string" then
       return t
     end
-    return table.concat(vim.iter(t):flatten(math.huge):totable(), "\n")
+    
+    -- Handle empty tables or tables with empty strings
+    local flattened = vim.iter(t):flatten(math.huge):totable()
+    local non_empty = vim.iter(flattened):filter(function(item)
+      return type(item) == "string" and vim.trim(item) ~= ""
+    end):totable()
+    
+    if #non_empty == 0 then
+      return "Unknown error occurred"
+    end
+    
+    return table.concat(non_empty, "\n")
   end,
 
   ---@param use_lsp boolean

lua/vectorcode/integrations/codecompanion/query_tool.lua

@@ -462,7 +462,21 @@ return check_cli_wrap(function(opts)
           args
         )
 
-        job_runner.run_async(args, function(result, error)
+        job_runner.run_async(args, function(result, error, code)
+          -- Check if this is actually an error or just empty stderr
+          local is_actual_error = code ~= nil and code ~= 0
+          local has_meaningful_error = false
+          
+          if type(error) == "table" then
+            -- Check if the error table contains any non-empty strings
+            local flattened = vim.iter(error):flatten(math.huge):totable()
+            has_meaningful_error = vim.iter(flattened):any(function(item)
+              return type(item) == "string" and vim.trim(item) ~= ""
+            end)
+          elseif type(error) == "string" and vim.trim(error) ~= "" then
+            has_meaningful_error = true
+          end
+          
           if vim.islist(result) and #result > 0 and result[1].path ~= nil then ---@cast result VectorCode.QueryResult[]
             local summary_opts = vim.deepcopy(opts.summarise) or {}
             if type(summary_opts.enabled) == "function" then
@@ -496,13 +510,22 @@ return check_cli_wrap(function(opts)
               })
             end)
           else
-            if type(error) == "table" then
-              error = cc_common.flatten_table_to_string(error)
+            -- Only report as error if we have a meaningful error or non-zero exit code
+            if is_actual_error or has_meaningful_error then
+              if type(error) == "table" then
+                error = cc_common.flatten_table_to_string(error)
+              end
+              cb({
+                status = "error",
+                data = error or "VectorCode command failed",
+              })
+            else
+              -- Successful operation but no results found
+              cb({
+                status = "success",
+                data = { raw_results = {}, count = 0, summary = "" },
+              })
             end
-            cb({
-              status = "error",
-              data = error,
-            })
           end
         end, tools.chat.bufnr)
       end,