fix(variables): parse stringified VARIABLE_ALIAS for FLOAT vars (go #22 last edge)

coerceToResolvedType only rescued stringified objects on the COLOR branch
(JSON.parse), so a FLOAT variable aliased to another FLOAT — when the client
stringified the alias object in transit — hit Number()→NaN and was rejected.
That is the exact asymmetry behind figma-mcp-go #22 (color aliases survived,
float aliases got stripped).

Lift the stringified-object rescue ahead of the per-type scalar coercion so it
applies to every resolvedType, deduping the COLOR JSON.parse in the process.
Pure widening: bare-string FLOAT ("abc") still rejects, COLOR bare string still
errors with the same message, native-object aliases unchanged.

Author: awdr74100

packages/plugin/src/handlers/set-variable-value.ts

@@ -12,18 +12,26 @@ import { toFigmaVariableValue } from './convert.js';
  */
 const coerceToResolvedType = (raw: unknown, resolvedType: VariableResolvedDataType): unknown => {
   if (typeof raw !== 'string') return raw; // native type survived transit — nothing to fix
+  // A stringified object is an alias ({ type: 'VARIABLE_ALIAS', id }) or RGBA color. Parse it back
+  // before any per-type scalar coercion so it survives for *every* resolvedType — notably a FLOAT
+  // variable aliased to another FLOAT, which the Number() branch below would otherwise NaN and strip
+  // (the asymmetry behind figma-mcp-go #22: COLOR aliases survived, float aliases didn't).
+  if (raw.trimStart().startsWith('{')) {
+    try {
+      return JSON.parse(raw) as unknown;
+    } catch {
+      throw new TypeError(`set_variable_value: "${raw}" is not valid JSON`);
+    }
+  }
   if (resolvedType === 'FLOAT') {
     const n = Number(raw);
     if (Number.isNaN(n)) throw new TypeError(`set_variable_value: "${raw}" is not a number`);
     return n;
   }
   if (resolvedType === 'BOOLEAN') return raw === 'true';
   if (resolvedType === 'COLOR') {
-    try {
-      return JSON.parse(raw) as unknown; // an alias / RGBA object that was stringified
-    } catch {
-      throw new TypeError(`set_variable_value: COLOR value "${raw}" is not valid JSON`);
-    }
+    // A COLOR value must arrive as a JSON object (RGBA or alias); a bare string is invalid.
+    throw new TypeError(`set_variable_value: COLOR value "${raw}" is not valid JSON`);
   }
   return raw; // STRING
 };

packages/plugin/test/handlers/set-variable-value.test.ts

@@ -73,6 +73,21 @@ describe('set_variable_value handler', () => {
     expect(setValueForMode).toHaveBeenCalledWith('M:0', { type: 'VARIABLE_ALIAS', id: 'V:9' });
   });
 
+  // The same go#22 alias, but stringified in transit (the client that stringifies COLOR's RGBA does
+  // it to alias objects too). The FLOAT branch must JSON.parse it back rather than Number()→NaN it.
+  it('parses a stringified VARIABLE_ALIAS back for a FLOAT variable', async () => {
+    const setValueForMode = vi.fn<() => void>();
+    const handler = createSetVariableValueHandler(
+      fakeFigma({ id: 'V:0', name: 'radius/md', resolvedType: 'FLOAT', setValueForMode }),
+    );
+    await handler({
+      variableId: 'V:0',
+      modeId: 'M:0',
+      value: '{"type":"VARIABLE_ALIAS","id":"V:9"}',
+    });
+    expect(setValueForMode).toHaveBeenCalledWith('M:0', { type: 'VARIABLE_ALIAS', id: 'V:9' });
+  });
+
   it('rejects a stringified FLOAT that is not a number', async () => {
     const variable = {
       id: 'V:0',