Add ISAC mechanic gap handoff actions

src/lib/components/isac/MechanicProgramEditor.svelte

@@ -55,7 +55,7 @@
 		disabled?: boolean;
 	} = $props();
 
-	let recipeKey = $state<TriggerActionKey>('same_target_hits_within_window');
+	let recipeKey = $state<TriggerActionKey | ''>('');
 	let recipeCount = $state(9);
 	let recipeWindow = $state(3);
 	let recipeDistance = $state(10);
@@ -118,13 +118,15 @@
 	}
 
 	function applyRecipe(replace = false) {
-		const result = createMechanicRecipe(recipeKey, recipeParams() as never);
+		if (!recipeKey) return;
+		const selectedRecipeKey = recipeKey;
+		const result = createMechanicRecipe(selectedRecipeKey, recipeParams() as never);
 		if (result.status !== 'supported') return;
 		const clauses = result.seed.clauses.map((seed, index): ConditionalMechanicClauseDraft => ({
-			key: `${slug(recipeKey)}-${rule.clauses.length + index + 1}`,
-			label: seed.label ?? TRIGGER_ACTION_REGISTRY[recipeKey].label,
+			key: `${slug(selectedRecipeKey)}-${rule.clauses.length + index + 1}`,
+			label: seed.label ?? TRIGGER_ACTION_REGISTRY[selectedRecipeKey].label,
 			event: seed.when,
-			recipeKey,
+			recipeKey: selectedRecipeKey,
 			if: seed.if ?? { kind: 'true' },
 			reducer: seed.reducer,
 			cooldownSeconds: seed.cooldownSeconds,
@@ -519,6 +521,7 @@
 				mode="single"
 				compact
 				subjectLabel="RECIPE"
+				emptySelectionLabel="NO RECIPE SELECTED"
 				bind:value={recipeKey}
 			/>
 			{#if ['same_target_hits_within_window', 'distinct_enemies_within_window', 'consecutive_same_target_hits'].includes(recipeKey)}
@@ -530,8 +533,8 @@
 			{#if ['target_hit_within_distance', 'within_distance'].includes(recipeKey)}
 				<label class="field">METERS<input type="number" min="0" step="any" bind:value={recipeDistance}/></label>
 			{/if}
-			<button type="button" class="secondary" onclick={() => applyRecipe(false)}>ADD RECIPE BRANCH ＋</button>
-			{#if rule.clauses.length}
+			<button type="button" class="secondary" disabled={!recipeKey} onclick={() => applyRecipe(false)}>ADD RECIPE BRANCH ＋</button>
+			{#if rule.clauses.length && recipeKey}
 				<button type="button" class="danger-quiet" onclick={() => replaceConfirmation = true}>REPLACE PROGRAM</button>
 			{/if}
 		</div>