In terms of using context, I wasn't really thinking of very young children just beginning their reading journey, but more for intermediate readers, reading books that don't have such carefully controlled vocabulary.
Perhaps we need to define terms before discussing any point!
This is what I was responding to:
But say I was new to reading, I wouldn't read, once upon a time there were three bears' as 'once upon a time there were three beers' even if I had only been taught 'ear' as the 'eer' sound and hadn't yet covered 'ear 'pronounced 'air'.
I'm not sure what you mean by an 'intermediate reader' but I would class a child who didn't know the alternative sounds for 'ear' as one who was 'new to reading' .
Whilst I am all for people listening to children read and using opportunities for incidental teaching, there will come a time when they will be on their own.
I think that you are overthinking this. Would you be expecting a child to be reading on its own before it has learned the common correspondences? (By 'common correspondences' I mean the 160 -180 ish correspondences most commonly encountered in words). In which case I think that it would be a bit unkind to leave a child reading unsupported, but that's just my opinion. I'm sure that there are loads of people around who think it is just fine to throw their children in at the deep end.
If it were a case of a child insisting on reading a book, which is beyond its known phonic capabilities, on its own then I would suggest that it is reminded that someone is available to help with any words it finds difficult. In the example you gave the text was so ludicrously easy (and the story, told orally, likely to be very familiar to the child) that suppying the word 'bear' would be almost a no brainer. However, if the child encounters a word that not only contains an unknown correspondence but is also not in their oral vocabulary no amount of context is going to help them. I would see this as possibly being the start of losing confidence and switching off from reading.
There are, though, so many variations on this scenario that I can't even begin to second guess what you are going to propose next.