what does MID: TID:$c8 mean? (EVAP code accompanied by P0446)

The monitor tests are described in the "1NZ-FXE ENGINE CONTROL SYSTEM — SFI SYSTEM" section of the Repair Manual (more info), under CHECKING MONITOR STATUS. The tests with Monitor ID $3D are all for the EVAP system. Oddly, the 2006 copy that I am looking at does not have a description for Test ID $C8, though it has C9, CA, CB, CD, CE, CF, D0, D1, D4, D5, and D7.

As your profile says 2007, maybe $C8 is a test that was added, or maybe it just was left out of this 2006 manual edition. Sometimes @Elektroingenieur is able to spot what happened there.

Your scan tool is showing enough to see that the test was trying to pull a vacuum of at least −0.294 kPa (about 2.2 mm of mercury) and the value didn't get vacuumy enough (by half).

If you look up the detection conditions and monitor description for P0446, a test for "Pressure switching valve is stuck OFF" is described, where it is considered stuck if pressure doesn't drop by "2 mmHg or more" during the test. So that seems to correspond well with what test $C8 is showing.

There are about 14 pages of troubleshooting workup in that P0446 section, and I can't really think of a useful "TL;DR" version. It might be necessary to just buckle down and follow the steps.

I do notice (again in this 2006 copy I'm looking at) that the "typical malfunction thresholds" table is a little garbled; it says "Either of following condition 1 or 2 is met", and then nothing is labeled as condition 2. That might also be something Elektroingenieur could find a less-garbled version of.