fix(copilot): prefer a conditioned variant over an unconditioned catch-all

An unconditioned same-id variant matches every set of values, so it would
shadow a genuinely selected variant purely by being declared first. Prefer
a variant that actually asserted something about the current values.

No block in the registry currently declares a catch-all ahead of a
conditioned variant on a field where it would change validation, so this
is a guard against the pattern rather than a fix for a live case.

Author: mzxchandra

apps/sim/lib/copilot/tools/server/workflow/edit-workflow/validation.test.ts

@@ -257,6 +257,22 @@ const multiVariantBlockConfig = {
       ],
       condition: { field: 'provider', value: 'beta' },
     },
+    // Catch-all declared first: it matches everything, so it must not shadow
+    // the conditioned variant below purely by declaration order.
+    {
+      id: 'mode',
+      type: 'dropdown',
+      options: [{ label: 'default', id: 'default' }],
+    },
+    {
+      id: 'mode',
+      type: 'dropdown',
+      options: [
+        { label: 'fast', id: 'fast' },
+        { label: 'slow', id: 'slow' },
+      ],
+      condition: { field: 'provider', value: 'beta' },
+    },
   ],
   tools: { access: ['multi_variant_tool'], config: { tool: () => 'multi_variant_tool' } },
 }
@@ -403,6 +419,18 @@ describe('validateInputsForBlock', () => {
       expect(result.errors[0].field).toBe('model')
     })
 
+    it('prefers a conditioned variant over an unconditioned catch-all', () => {
+      // `mode` declares the catch-all first; it must not shadow the beta variant.
+      const result = validateInputsForBlock(
+        'multi_variant_block',
+        { provider: 'beta', mode: 'fast' },
+        'mv-7'
+      )
+
+      expect(result.errors).toHaveLength(0)
+      expect(result.validInputs.mode).toBe('fast')
+    })
+
     it('falls back to the union when no variant condition matches', () => {
       // Without a provider nothing resolves, so widen rather than guess.
       const result = validateInputsForBlock('multi_variant_block', { model: 'b1' }, 'mv-6')

apps/sim/lib/copilot/tools/server/workflow/edit-workflow/validation.ts

@@ -326,7 +326,13 @@ function resolveActiveSubBlock(
   const active = candidates.filter((candidate) =>
     evaluateSubBlockCondition(candidate.condition, effectiveValues)
   )
-  return active.length > 0 ? active[0] : null
+  if (active.length === 0) return null
+  /**
+   * An unconditioned variant matches everything, so it would shadow a genuinely
+   * selected one purely by being declared earlier. Prefer a variant that
+   * actually asserted something about the current values.
+   */
+  return active.find((candidate) => candidate.condition) ?? active[0]
 }
 
 /**