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>

docs/ROADMAP.md

@@ -555,6 +555,22 @@ Design/decision records and a running log of shipped work (items marked
   `%26`, `%3F`, `%23`, `caf%C3%A9`. **Unverified on purpose:** whether each
   vendor's page fills the box or auto-submits — testing that means posting into
   Bernardo's own accounts.
+- ✓ **The #107 compat shim is pinned (#133, 2026-07-16):** `mkFlake` prefers
+  `state.json` and still accepts the legacy `theme-state.json`, because a
+  machine only migrates on its next menu write — but nothing evaluated a
+  checkout carrying **only** the legacy name, so the shim could rot with every
+  check green, breaking rebuilds for exactly the users who have not touched the
+  menu since #107 (i.e. the least likely to notice). `checks.state-legacy-name`
+  now evaluates two fixtures: legacy-only must resolve, and **no state at all
+  must still throw** — the fail-closed gate is half the shim's contract 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` — which is why the fixture is
+  one file and the check costs no measurable time. 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. Both assertions were proven by breaking
+  `lib.nix` — deleting the fallback, then defeating the gate — and watching each
+  fail by name. Delete it with the shim and the `nomarchy-theme-sync` alias.
 - ✓ **The VM's verdict on menu geometry is worthless — and so is measuring
   (#132, 2026-07-16):** the guest draws the picker with icons at ~¼ of
   `ui.iconSize` and rows short enough to clip a 6-row root, so screenshots are