test(state): #133 — pin the #107 legacy-name shim (and its fail-closed gate)

mkFlake prefers state.json and still accepts the legacy theme-state.json,
because a machine only migrates on its next menu write. Nothing evaluated a
checkout carrying ONLY the legacy name, so the shim could rot with every
check green — breaking rebuilds for precisely the users who have not opened
the menu since #107, i.e. the ones least likely to see it coming.

checks.state-legacy-name evaluates two fixtures: legacy-only must resolve,
and no-state-at-all must still throw. The gate is half the shim's contract
(it turns "no state file" into one readable error instead of a readFile
stack from inside the module system) and was equally unpinned.

Cheap by construction: mkFlake wraps its return in `builtins.seq
_themeState`, so forcing the attrset forces the state read and nothing else
— no module system, no home.nix. Hence a one-file fixture and no measurable
cost (flake check still ~35s). That file is a SYMLINK to the shipped
template's state.json: a copy would drift and the check would quietly start
testing a fossil. The fixture also asserts it has no state.json, or it would
pass while testing nothing.

Both assertions proven by breaking lib.nix — deleting the fallback, then
defeating the gate — and watching each fail by name. Delete this check
together with the shim and the nomarchy-theme-sync alias.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -153,18 +153,6 @@ whether Nomarchy holds itself higher — darker label, or a darker accent mix
 for light palettes — and note `tools/check-theme-contrast.py` covers palette
 pairings only, never GTK widget surfaces. `[human]` for the aesthetic call.
 
-### 133. No check pins the #107 legacy-name compat shim
-
-`lib.mkFlake`, doctor and lifecycle all still accept `theme-state.json`, and
-`nomarchy-state-sync` migrates it on write — but nothing in `checks.*`
-evaluates a checkout that has *only* the legacy name, so the shim can rot
-silently while every check stays green. It is load-bearing until every
-existing machine has taken one menu write. Add a cheap eval check: a fixture
-dir with `theme-state.json` only → `mkFlake` resolves it; plus the write-side
-migration (state.json created + git-staged, legacy `git rm`'d). Proven by
-hand 2026-07-15 (drvPaths identical across the rename) — this just keeps it
-proven. Delete together with the shim + the `nomarchy-theme-sync` alias.
-
 ### 143. Rofi keeps the selected *row number* when the search changes, so the highlight lands on an unrelated entry
 
 Bernardo 2026-07-16, and his repro is exact: open the app menu, type `ca`, move