-yu is Officially Productive on Si-verbs

Original question text:

> The -yu suffix is known to be productive with verbs, to make the "one who <verb>s" form- **taronyu**, **karyu**, **saylahe**. We also have examples of si-verbs made into this form: **tsamsiyu**, **srungsiyu**, and **stiwisiyu** for example. However, in looking through the archives, we cannot find confirmation that -yu is definitively productive with si-verbs. (we did find conflicting statements for and against productivity, but none had sources so we dismissed them.) Are you able to clarify this, once and for all, at this time?
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Original correspondence text:

> I see no reason that -yu with si-verbs should be any less productive than with single-word verbs.
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> Notice, though, that I've stated that carefully: in other words, *-yu is productive with si-verbs to the same extent it's productive with "regular" verbs*. But that leaves open the question, just how productive is -yu with verbs in general?
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> It's very similar to the question of how productive agentive -er is in Engish. You can pretty much add -er to any verb to get an agent, a "one who" person: talk/talker, write/writer, interpret/interpreter, etc. (An exception would be a verb like "seem": I don't think we can say \*seemer.) But although we can do this technically, would all such -er nouns be useful and normal-sounding? What about "wanter," meaning one who wants? (I notice that Spell Check is putting squiggly red lines under both "seemer" and "wanter," even though my online dictionary lists "wanter" as a legitimate word.) What about "putter," not in the sense of the golf club but rather as "one who puts (say, a glass on a table)?
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> What about "closer"? Would you ever say, "Who was the closer of the door?" rather than simply "Who closed the door?"
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> That last example is instructive, I think--because "closer" is in fact a legit word with a specialized meaning: in sales, one who "closes the deal" and gets the customer to sign on the bottom line.
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> This illustrates that the -er suffix, although considered productive, is mainly used to indicate a person who regularly engages in some recognized activity or plays some acknowledged role in society: teacher, interpreter, street cleaner, pitcher, catcher, hunter, etc. (In English, unlike -yu in Na'vi, -er can also indicate a tool used for the activity: washer, dryer, etc.)
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> On the other hand, we do have uses of -er that don't indicate societal roles. "Hearer" doesn't refer to any kind of recognized occupation or occupation, but we can say things like "The speaker sends the message and the hearer interprets it."
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> So that's pretty much how -yu works in Na'vi: By and large, it's used to indicate someone who engages in some activity on a regular basis and often plays a particular role in society: as you said, **karyu**, **taronyu**, **tsamsiyu**, **srungsiyu**,  . . .  However, it can sometimes be used simply to indicate the person doing the verb, as in: "**Stawmyul 'upxaret ralpeng**." For that reason, we have to consider -yu productive, even though there are many potential -yu forms that will never be used.
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> Hmm. That was more convoluted than I had originally thought!
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Original question text:

> Thank you for the insights. Does this mean that **tsam si** could be inferred to be a word by the existence of **tsam** and **tsamsiyu**?
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Original correspondence text:

> Yes, there should be a si-verb **tsam si**! That was an omission. I'll have to think about whether it means "make war," i.e. initiate a war, or "engage in warfare." But it should be in the dictionary.
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*Originally received on October 30th, 2020*