How much character growth crosses the line into breaking the character
(not a duplicate of Character Development - How much is too much? because that one is more about "overreaction" to smaller events.)
TL;DR: How much can a character change without becoming unrecognizable? How can you indicate character growth (causes/effects) efficiently?
I was listening to Worm and "We've Got Worm" (a long web-serial turned into a fan audio project, and a podcast discussing the writing choices in Worm, and I was struck by something.
Often the hosts of the "We've Got Worm" podcast praise a character for "growing so much" either behind the scenes, or especially our main character.
Now the main character's main transition, from mousy pale high school sophomore who is bullied to confident leader who often over-escalates her responses to things is extreme, yet it makes sense given step-by-step what has happened to her. (Gaining Powers, gaining friends, disasters strike but she tries to help, repeat disasters/help a few more times.) She's still "recognizable" the whole time.
Because Worm is a web-serial running over 1.5 million words (and I'm at arc 15, about one-third through, in this re-listen), the author has time to step us through all of these changes.
But in my writing -- I don't have that length! In a novel of a "normal" length (60,000-120,000 words?), how can you indicate character growth without taking an entire 10,000 word interlude about them?
And how do you limit it so each character still acts "in character" even if it's a bolder or shyer version of their prior self, and isn't just acting differently because Plot Demands Someone Do X?