alt key combinations not working

alt key combinations, with or without remapping to esc, are not working as expected, as in the "Use Option as Meta key" in Apple Terminal.

I expect:
alt-f/alt-b to move forward and backward over a word
alt-d to delete the word ahead.
... readline/emacs-style actions.

Example misbehavior:
With alt mapped to esc: type alt-f, does nothing, alt-f again prints "f".
With alt set to None: type alt-f prints special-script-function-f.

I think I want alt-f to send: "\x1bf".
For the alacritty terminal app on MacOS, I have a config line like this:
- { key: F, mods: Alt, chars: "\x1bf"}

Hardware:
iPhone 7
bluetooth Apple keyboard (A1314)

iOS 10.2.1
Blink: v5.028.1. Feb 28 2017

Start by reproducing the Alt-key behavior described for the iPhone 7, Apple keyboard, and Blink on iOS. Trace the terminal input path for Alt combined with f, b, and d, using the Apple Terminal and Alacritty escape-sequence examples as references. Done means these combinations produce the expected readline/Emacs-style actions, including the intended escape-prefixed sequence.

Written by the indexing model from the issue text.