In reply to:

longest charlinkade FORESTALL: FOREST, ALL; FORE, REST, TALL (9)

notice the "link" part of charlinkade. the words listed in the two groups *link the characters of forestall. the word ore is also contained therein, but doesn't work.

In the word 'therein' there nests a veritable forest of linguistic creatures. And 'therein' itself nests in 'thereinbefore', an even more fertile progenitor of nested words.

As for agglutinative or pyramid or curtailed words, the longest string I've seen started with about 13 letters, but my favourite (only because I thought it up myself), at 11, is:

austringers
astringers
stringers
stringer
stinger
stinge
singe
sing
sin
in
I

An austringer, as I'm sure you all know, is a variant spelling (in OED) of the word for 'a keeper of goshawks'.