Things: containers, tools, and hiding places

Containers and supporters, with limits

create the travelling trunk
  aka trunk
  a container with max items 3
  openable
  in the Study

create the mantel
  aka mantelpiece, shelf
  scenery, a supporter with capacity 2
  in the Entrance Hall

in and on placement lines put things inside/atop other things at load; capacities are config on the kind. Note the article in placement and naming lines: the grey overcoat, not a possessive like Verity's overcoat (a leading possessive parses as a trait adjective).

The declarative capability family: headline pattern

This is the family to internalize. Wherever an action needs a specific instrument, you declare the capability with the instrument named on it, with no key tables and no handlers:

create the cellar door
  a door, lockable with the tarnished key

create the nailed crate
  a container
  openable with the crowbar

create the kipper tin
  a container
  openable with the tin opener

create the fuse
  cuttable with the garden shears

create the deed box
  a container
  openable with the silver locket

open the crate with the crowbar, cut the fuse with the shears, unlock the door with the key: all of it works from these single lines, and each refuses legibly without its instrument. If you find yourself wishing for unlockable by the key: you already have it, spelled lockable with the tarnished key.

Fernhill chains the family into its opening puzzle: the crowbar (cellar) opens the crate, the crate holds the tin opener, the opener opens the kipper tin, and the kipper matters in the next chapter.

Concealment and searching

create the tarnished key
  aka key
  concealed
  on the doormat

A concealed item is invisible until the player SEARCHes its holder: the doormat gives up the cellar key, the grey overcoat's pocket gives up the winding key. The study curtains show the companion pattern, a place to hide yourself: hiding-spot with position behind.

Readables, two ways

create the half-burned letter
  readable with text "…arrangements with the county bank, where the deed may rest secure until…"

create the diary page
  readable
  states: folded, read

  on reading it
    change it to read
    phrase diary-text
      "K. says the greenhouse will take the worst of the frost…"
  end on

Short texts fit on the config form; anything that should do something when read gets an on reading it clause: the diary flips its own state (the gated-detail chapter builds on read) and speaks its text. The half-burned letter, incidentally, is a red herring: it points to the bank, and it is wrong.

Wearables

create the grey overcoat
  aka overcoat, coat, verity's overcoat
  wearable, a container

wear the overcoat works; the pocket (it's also a container) carries the concealed winding key.

Scenery discipline

Every noun the prose mentions exists: lime trees, the dry fountain, the copper pans, the wall niche, the scorched dome. Each is two lines and a description:

create the fountain
  aka basin
  scenery
  in the Fountain Court

  A dry stone basin drifted with last summer's leaves.

scenery means fixed in place and quietly present. This is craft, not a feature: a player who examines what you wrote about should never hear "You can't see any such thing."