Oooooh, “flowcharts”! (Said like Homer Simpson thinking of donuts! LOL) Don’t see them often these days, kinda miss em a bit… LOL
So, the answer is yes and no. If you are using PHP and you redirect to another page, there is no need to handle a HTTP browser response code. If the include has a bad error, it will “break” the page more often than not. This will not generate much of an error, but, will just break the page. (As far as I know.)
For error messages and pages, I have used them in this manner. I create a nice error message page that looks like the rest of the site, but, without the “fluff” on it. (No ad’s, not as fancy…) It contains three or four areas that contain Heading, Error-Message, Error-Details and a return link of some sort. I load these into SESSION variables and send the user to that page. They see a page similar to the rest of the site, but, with a nice, YOU-MESSED-UP header, with what the error message is and the “details” on how to fix it and how not to let it happen again. These are all sent from the page that located the error and creates the text for each of these items.
In your flowchart, you mentioned database connection failures. These should be handled in the connection code itself. If the connection fails, that code should contain it’s own error handler for that section. But, since the page can not connect to the DB, it needs to end anyways, so loading up a few SESSION variables and redirecting to the the error-message page is okay. The return links sent to it would be to return to somewhere before the connection was tried. If it was a login page, as an example, the return link would be to the login page.
Of course with the new validation routines, most of these types of errors are just done by a pop-up alert or by a DIV tag which just appears from nowhere with the error message inside it.
I also noticed in your flowchart you mention developer vs. user. So, I am assuming your site does some sort of dual access on pages. One for common user’s and one for developers. This can be confusing. Most sites separate their developers from their users. They have ADMIN control panels for the developers and the users use the rest of the site.
Well, I am one that always gives way too much information, but, like people to think outside the box a bit.
Once you have another question, let us know… Good luck!