📝 Note the gate in changelog and backlog

Close the broad-universe type-hole task and cancel the widened-literal
test task, since arbitrary strings no longer fall through to a fallback.

backlog.tasks

@@ -37,12 +37,12 @@ Testing:
     ✔ Rewrite `src/util/__tests__/lsp-completion.ts` onto `createMessageConnection` and typed requests @done
     ✔ Update `development/testing.md § Autocomplete` for the new client @done
     ✔ Run `npm run verify` and check the task off @done
-☐ Test a literal union widened with `(string & {})` — `"red" | "green" | "yellow" | (string & {})` @medium
-    → autocomplete should still offer the literals; arbitrary strings stay assignable and fall through to the fallback
-☐ Type hole when using broad types like string as a universe @high
-    ☐ handlers cannot be exhaustive, yet it is possible to not have a fallback
-    ☐ one test even exploits this, I think for a negative test
-    ☐ does the same type hole exist for tagged-union matchers or primitive-union matchers only?
+✘ Test a literal union widened with `(string & {})` — `"red" | "green" | "yellow" | (string & {})` @medium @cancelled
+    → broad universes are rejected; the rejection is covered by the broad-universe gate tests
+✔ Type hole when using broad types like string as a universe @high @done
+    → decided: broad universes are rejected at the factory, so the exhaustive overload can always be proven
+    → value/stringification collisions (`true | "true"`, `1 | "1"`) are rejected too; handler params are typed by `Member<T, K>`
+    → see development/library.md § Supported universes
 
 Matcher:
 ✔ Clean up: adopt the 3-overload matcher (`src/prototype-ac2.ts`) and delete the prototypes @high @done