manual tests for the protocol with the driver

I need to get more rigorous about the error handling.

Manual_tests.md

@@ -13,6 +13,65 @@ record those here.
     - where exactly the cursor is drawn to highlight a given character
     - analogously, how a shape precisely looks as you draw it
 
+### Protocol with driver; error-handling
+
+* clone this repo to a new client app, clear its save dir[1], run it, run the
+  driver, add a definition:
+    ```
+    on.draw = function()
+    end
+    ```
+  Hit F4. No error.
+  Quit driver, quit client app. Restart client app. No error.
+
+* clone this repo to a new client app, clear its save dir, run it, run the
+  driver, add a definition that draws to screen:
+    ```
+    on.draw = function()
+      love.graphics.print('hello!', 50,50)
+    end
+    ```
+  Hit F4. Client app shows 'hello!'
+  Quit driver, quit client app. Restart client app. No error. Client app shows 'hello!'
+
+* clone this repo to a new client app, clear its save dir, run it, run the
+  driver, add a definition containing invalid Lua:
+    ```
+    on.draw = function(
+    ```
+  Hit F4. Driver shows an error under the definition.
+
+* clone this repo to a new client app, clear its save dir, run it, run the
+  driver, add a definition containing invalid Lua:
+    ```
+    on.draw = function(
+    ```
+  Hit F4. Driver shows an error under the definition as before.
+  Quit the client app. The invalid code is saved in file 0002-on.draw in the
+  save dir. However, the file 'head' in the save dir contains '1'.
+  Restart the client app. It loads up without error.
+  Switch back to the driver. Fix the definition.
+    ```
+    on.draw = function()
+    end
+    ```
+  Hit F4. The error disappears.
+
+* clone this repo to a new client app, clear its save dir, run it, run the
+  driver, add a definition containing invalid Lua:
+    ```
+    on.draw = function(
+    ```
+  Hit F4. Driver shows an error under the definition as before.
+  Quit the client app. The invalid code is saved in file 0002-on.draw in the
+  save dir. However, the file 'head' in the save dir contains '1'.
+  [Don't restart the client app.]
+  Switch back to the driver. Hit F4. The driver hangs and needs to be
+  force-quit. [This is not ideal, but how things are today.]
+
+[1] We never clear the app from the driver's config. driver.love needs to be
+robust to apps changing out from under it.
+
 ### Other compromises
 
 Lua is dynamically typed. Tests can't patch over lack of type-checking.