fix(journal): unify $var lookup and error

EvalContext.lookup now receives the full $var name, matching getCombined,
setBase, and getMods, and parseFactor throws "Unknown variable" when the
lookup returns undefined. /set and /roll use the new resolveVariable() so a
typo errors instead of silently evaluating to 0.

Declarations and tag modifiers stay lenient (unknown -> 0): the documented
$hp = $con*5+$mod_hp pattern depends on external/undeclared variables
defaulting to 0.

src/components/journal/command-dispatcher.ts

@@ -11,7 +11,7 @@ import { parseInput } from "./command-parser";
 import { resolveRollPayload } from "./types/roll";
 import { resolveSparkPayload } from "./types/spark";
 import { evaluateExpression, exprValueToString } from "./variable-expression";
-import { computeCascade, getCombined, setBase } from "./var-reactivity";
+import { computeCascade, getCombined, resolveVariable, setBase } from "./var-reactivity";
 import { ensureReactivity } from "./completions";
 
 // Tagmap pattern: "#warrior:1;#druid:2". Also accepts bare "#tag" as shorthand.
@@ -131,7 +131,8 @@ export async function dispatchCommand(
     if (arg.includes("$")) {
       try {
         const ev = evaluateExpression(arg, {
-          lookup: (name: string) => getCombined("$" + name, ctx.variables),
+          // Strict: referencing an undefined variable is an error, not 0.
+          lookup: (name) => resolveVariable(name, ctx.variables),
         });
         if (ev.value.kind !== "number") {
           return finish({ ok: false, error: "Roll expression must evaluate to a number" });
@@ -204,11 +205,8 @@ function dispatchSet(
     } else if (p.expr) {
       // Evaluate expression — handles both numeric and tagmap values
       const result = evaluateExpression(p.expr, {
-        lookup: (name: string) => {
-          const k = "$" + name;
-          // Use getCombined with stream fallback for accurate values
-          return k === key ? undefined : getCombined(k, ctx.variables);
-        },
+        // Strict: referencing an undefined variable is an error, not 0.
+        lookup: (name) => resolveVariable(name, ctx.variables),
       });
       newValue = exprValueToString(result.value);
     } else {