paskening tzaraas al tnai

If you're still a reader here you know in the past few weeks we've been doing some of R' Shteinman's torah on the parsha.  It's shabbos ha'gadol and everyone is into inyanei Pesach, but at this point I feel bad skipping a week.  

R' Shteinman raises the question of whether a kohen can be metaheir a metzora al tnai.  Tos (Kesubos 74) holds that you can only make a tnai in a matter that lends itself to shlichus (see this post).  The ability to appoint a shliach to take care of something indicates that you have control over the outcome, and that is the key ingredient necessary in order to be able to make a tnai that will effect the outcome.  In the case of tzaraas, the kohen has to personally declare whether something in tamei or tahor -- he cannot appoint a shliach to do so on his behalf.  It would seem, therefore, that he cannot make a tnai either.

There seem to be exceptions to the above rule, e.g. you can make a tnai in nezirus (see Tos Nazir 11), or in nedarim.  R Akiva Eiger writes that someone who is afraid that they will miss zman krias shema should read shema before davening al tnai that if they make the zman during birchos krias shema, they want to be yotzei only with the later recitation with the brachos. You can't have a shliach read k"s for you, so this sounds like yet another exception to the rule.  A number of Achronim hold that Tos rule is limited to cases where an action is being done.  However, when it comes to dibur -- the case of neder, nezirus, etc. -- a tnai can be made to undo dibur even if a case where a shliach cannot be appointed.  This would seem to cover the declaration of the kohen as well.

The reason R' Shteinman has this on his radar is because Rashi at the beginning of the parsha quotes a din ביום טהרתו – מלמד שאין מטהרין אותו בלילה.  What would happen if the kohen saw the nega during the day, and declared it tamei or tahor al tnai that the psak goes into effect after dark?  Is it the maaseh of psak at night which is barred, or is it the chalos of the psak?  Would such a tnai even work?  (This is reminiscent of R' Akiva Eiger's safeik with regards to the issur of mekach u'memkar on shabbos -- is it the act of buying/selling which is prohibited, or is it the chalos of the sale?  What if you made a sale on Friday which is chal on Shabbos?)  

Later on in the parsha (14:36) by nigei batim there is a din  וְצִוָּ֨ה הַכֹּהֵ֜ן וּפִנּ֣וּ אֶת־הַבַּ֗יִת בְּטֶ֨רֶם יָבֹ֤א הַכֹּהֵן֙ לִרְא֣וֹת אֶת־הַנֶּ֔גַע to clear out the house before the kohen comes to pasken on the nega afflicting it so that the kelim inside do not become tamei.  If it is possible to pasken on a nega al tnai, why couldn't the kohen give his psak al tnai that it does not take effect for another hour or however long so that the house can be cleared?  It seems from here that tnai does not work.

R' Shteinman rejects this proof.  Forget about tnai; one can ask more fundamentally why the house needs to be cleared before the kohen gets there -- let the kohen just hold off on paskening until the kelim are removed?  It must be (as Ohr haChaim spells out) that the kohen is obligated to pasken as soon as he sees the nega and put the house in a state of hesger, if required.  By that same token, tnai cannot work either because of that same obligation to enforce hesger as soon as the nega is seen.

2) Rashi comments that nigei batim is a gift from Hashem.   וְנָתַתִּי֙ נֶ֣גַע צָרַ֔עַת בְּבֵ֖ית אֶ֥רֶץ אֲחֻזַּתְכֶֽם Rashi writes 

בשורה היא להם שהנגעים באים עליהם, לפי שהטמינו אמוריים מטמוניות של זהב בקירות בתיהם כל ארבעים שנה שהיו ישראל במדבר, ועל ידי הנגע נותץ הבית ומוצאן.

R' Shteinman points out that the gemara implies that negaim come as punishment for sin.  How then can Rashi tell us that Hashem did this in order to give a person a rewrd and allow them to find buried treasure?

He answers that there is no contradiction.  A person might need to receive a punishment, but at the same time, Hashem can bless them with a buried treasure.  Had they not sinned, they might have gotten that treasure without having to destroy their house, but given the circumstances, this is how it had to work out.