quoted

Sure it won't break anything, but it won't work either!  The existing 
message hook runs after the editing session -- I want the hook to 
introduce text that is merely a suggestion that the user can delete, or 
a template that the user needs to customize further.

OMG you're right.  But why didn't you say so in the commit message?  
Something like "This hook complements the commit-msg hook, in that it runs 
_before_ the editor is launched".

I can't believe this. ;-)  At least I'm laughing for something nice now!

You're right, I should have said instead of this:

The prepare-commit-msg hook is run whenever a "fresh" commit message 
(i.e. not one taken from another commit with -c) is shown in the editor. 

... just before a "fresh" commit message is shown in the editor.
          ^^^^^^

quoted

quoted

Also, the change would be non-intrusive, easy-to-review

Please.  That's ludicrous.

My patch is 3 lines of inserted code and 0 modified lines, checking one 
variable that is set once in builtin-commit.c (edit_message).

Actually, after reading the commit message I was in 
"this-is-not-necessary" mode, and therefore the diffstat looked too large 
for me.

Yes, but still the diffstat was all .txt files... ;-)

Actually, reading your patch again I think it also triggers for "-c", as 
well as for "[-C|-F|-m] ... -e".

Not for "-c", that's the point of the "edit_message" check.  You're 
right about "-e" though.

Points taken, and patch will be resubmitted after 1.5.4.

Paolo