Bug#306290: ITP: ttf-mph-2b-damase -- font with ranges from the latest version of unicode
I was interested to see that you had taken the trouble to make a Kharosthi font. It is exciting to see that people have noticed that Kharosthi is now part of Unicode, and a complement to our efforts to have it included in the first place, Thank you!
As for the font, as Stefan has pointed out, and you are aware, Kharosthi is a complex font, and not surprisingly, you haven't made OpenType tables (yet). I made the font which is used in the Unicode tables - and have expermimented with various GSUB AND GPOS tables, but no software currently supports these tables, so the fact that the tables are lacking in your font is rather mute for the time being.
In answer to your question,
Is there an actual vowel-killer symbol in Kharosthi?
No, there is no explicit symbol in Kharosthi for halant, hence the control symbol. In the very few cases in where a halant-form of a sign is attested in the literature, it is formed by writing it as a subscript. When I create the OT tables for this character, I will map to a duplicate set of the base glyphs which are approximately 50% of full size and set lower on the writing line.
For further information about Kharosthi, please check the Unicode proposal, and my MA thesis.
I am currently working on a revised version of my Gandhari Unicode font, once work on this is complete, I will finish adding OpenType tables to the Kharosthi font I have prepared. If you are interested, I will let you know when work on this is complete.
Best wishes and congratulations for producing the first Kharosthi Unicode font available on the internet.