Based on its most prototypical use (you doing it when you’re in a close call) I think I would call it an interjection. It is certainly not an ideophone, ideophones being subjective evocations of perceived events rather than reactions to events.

Linguists have made different sorts of distinctions within the category of interjections. According to one influential categorization (Ameka 1992) I think this would classify as cognitive and/or emotive, rather than, say, conative or phatic. As Ameka writes:

The emotive ones are those that express the speaker’s state with respect to the emotions and sensations they have at the time. For example, Yuk! ‘I feel disgust’; Wow! ‘I am surprised’; Ouch! ‘I feel pain’; Ugh! ‘I feel disgust’ (see Wierzbicka 1992). Cognitive interjections are those that pertain to the state of knowledge and thoughts at the time of utterance. Examples include: Aha! ‘I now know this’; (Ewe) ehe! ‘I now remember’.
(Ameka p. 113)

Ameka, Felix K. 1992. Interjections: The Universal Yet Neglected Part of Speech. Journal of Pragmatics 18, no. 2-3: 101-118.

Your Japanese examples are interesting. I can think of a couple of similar examples in Siwu — e.g. the expression “ɣààà” for surprise, which always comes with the ‘jaw open, eyebrows raised’ facial expression, is borderline interjection/ideophone and I would have difficulty deciding on a category.

As for the Siwu examples cited in my post, they are supposed to be within the scope of the irony of that paragraph. In fact they would never be used like that; they would rather be used in constructions and contexts like those outlined here.

Your post reminds me of some facts about Japanese mimetics that have not been stressed before.

First, interjections (e.g., E? ‘What?’, Haa ‘Sigh’) often appear in soliloquy, but (interjectional) ideophones are by far less likely to. This difference seems to support the “sound symbolic involvement” hypothesis. We use ideophones for communication.

Second, there are some emotion mimetics of interjectional origin (e.g., hat(-to) ‘startled’ < Ha’ (gasp), hot(-to) ‘relieved’ < Ho’ (sigh of relief)). They instantiate the emotive “semantics” of interjections.

Third, the Siwu ideophones you give in the third section headed “Ideophones are not responses” look a little bit different from Japanese mimetics with similar meanings. We can use some mimetics interjectionally (e.g., Dokaan! ‘Baang!’) but cannot use others (perhaps less iconic ones) so (e.g., *Kuyokuyo! ‘Worrying!’). This seems to suggest the graded nature of “interjectionality” or “ideophonicity”.

How about Siwu ideophones?

Best,

Kimi