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Comments

Your HCONS lists are still broken because you didn't
add no-hcons-lex-item as a supertype of noun-lex, per
the Lab 6 instructions.  Please fix this.

Your semantic representations are broken in examples
with embedded clauses, because embedding-verb-lex
doesn't inherit from any linking type in the matrix.
The lab instructions suggested clausal-second-arg-trans-lex-item,
which should work.

embedding-verb-lex := verb-lex &
  [ SYNSEM.LOCAL [ CAT.VAL.COMPS < [LOCAL [ CAT [ HEAD comp,
						  MC - ],
					    CONT.HOOK.INDEX.SF #sf ] ] >,
		   CONT.HOOK.INDEX.SF #sf ]] .

 I also have a problem where these irules don't appear to be applying
 as mandatory, so zero-marked verbs seem to parse just fine everywhere.
 Thus, I haven't been able to ensure that they are correctly staying
 out of embedded clauses. Below are some examples that should be
 a test case, however.

I suspect it's because you never said [INFLECTED -] on verb-lex.
The phrase structure rules want daughters which are [INFLECTED +],
but your verbs are starting of underspecified for this feature.
 
 In Arabic, this special verb form is the zero-marked stem of the verb,
 so I made an imperative-lex-rule lrule of type
 const-add-only-ltol-rule that added the constraint [ FORM imp ] to the
 verb.

const-add-only-ltol-rule suggests that you might have additional
affixes attaching later, which would seem inconsisten with your
description. I think you want const-ltow-rule.  (That one takes
an [INFLECTED -] daughter and produces an [INFLECTED +] mother.)