In my research of Torah inerrancy, and following my other question "why-there's-no-deoraytah-prohibition-of-altering-torah-scroll", I notice that the Mishnah does not mention any Halachot of writing a Kosher Torah scroll. If I understand correctly, the first systematized approach to writing Torah is Masechet Sofrim, dated to Geonim time (8th century CE and on).
It seems absolutely fundamental to me that one of the primary concerns of the Jewish Halachah should be the importance of letter-exact copying of our Torah scrolls, as the Gemmorah in Eruvin 13:
בְּנִי, הֱוֵי זָהִיר בִּמְלַאכְתֶּךָ, שֶׁמְּלַאכְתְּךָ מְלֶאכֶת שָׁמַיִם הִיא, שֶׁמָּא אַתָּה מְחַסֵּר אוֹת אַחַת אוֹ מְיַיתֵּר אוֹת אַחַת — נִמְצֵאתָ מַחֲרִיב אֶת כָּל הָעוֹלָם כּוּלּוֹ.
He said to me: My son, be careful in your vocation, as your vocation is heavenly service, and care must be taken lest you omit a single letter or add a single letter out of place, and you will end up destroying the whole world in its entirety. [Addition or omission of a single letter can change the meaning from truth [emet] to death [met].
See also Maharal in Tiferet Israel.
Given the importance of the subject, why didn't Rebbi mention any Halachot of writing a Kosher Torah scroll in the Mishnah?