fix: strip opening code fence not on first line and discard preceding lines

Author: evanmcneely

lua/enlighten/ai/anthropic.lua

@@ -147,15 +147,25 @@ function M.create_text_filter(feature)
       pending = pending .. text
 
       if not first_line_checked then
-        local newline_pos = pending:find("\n")
-        if not newline_pos then
-          return "" -- Still accumulating first line
+        -- Skip blank/whitespace-only lines to find the first line with content
+        while true do
+          local newline_pos = pending:find("\n")
+          if not newline_pos then
+            return "" -- Still accumulating a line
+          end
+          local line = pending:sub(1, newline_pos - 1)
+          if line:match("^%s*$") then
+            -- Blank line, discard and keep looking
+            pending = pending:sub(newline_pos + 1)
+          else
+            -- First line with content: check for code fence
+            if line:match("^```") then
+              pending = pending:sub(newline_pos + 1)
+            end
+            first_line_checked = true
+            break
+          end
         end
-        local first_line = pending:sub(1, newline_pos - 1)
-        if first_line:match("^```") then
-          pending = pending:sub(newline_pos + 1)
-        end
-        first_line_checked = true
       end
 
       -- Find the last newline - hold back everything after it (potential closing fence)

tests/unit/anthropic_provider_spec.lua

@@ -217,5 +217,33 @@ describe("provider anthropic", function()
       collected = collected .. filter.flush()
       equals("print('hi')\n", collected)
     end)
+
+    it("should strip opening fence preceded by blank lines", function()
+      local filter = anthropic.create_text_filter("edit")
+      local collected = ""
+      collected = collected .. filter.process("\n\n```go\nfunc main() {\n")
+      collected = collected .. filter.process("}\n")
+      collected = collected .. filter.flush()
+      equals("func main() {\n}\n", collected)
+    end)
+
+    it("should strip opening fence preceded by blank lines across chunks", function()
+      local filter = anthropic.create_text_filter("edit")
+      local collected = ""
+      -- First chunk is just blank lines, no content line yet
+      collected = collected .. filter.process("\n\n")
+      -- Second chunk has the fence and code
+      collected = collected .. filter.process("```go\nfunc main() {\n}\n")
+      collected = collected .. filter.flush()
+      equals("func main() {\n}\n", collected)
+    end)
+
+    it("should strip opening fence preceded by whitespace-only lines", function()
+      local filter = anthropic.create_text_filter("edit")
+      local collected = ""
+      collected = collected .. filter.process("  \n\t\n```lua\nlocal x = 1\n")
+      collected = collected .. filter.flush()
+      equals("local x = 1\n", collected)
+    end)
   end)
 end)