fix(frontend): skip reserved ids when auto-assigning flow module ids (#10651)

* fix(frontend): skip reserved ids when auto-assigning flow module ids

* test: state the reserved-id invariant only beside the implementation

frontend/src/lib/components/flows/flowModuleNextId.test.ts

@@ -50,4 +50,9 @@ describe('nextId', () => {
 		const state = stateWith([...ids, 'process', 'my_step', 'failure'])
 		expect(nextId(state, flowWith(ids))).toBe('c')
 	})
+
+	// "as", the successor of "ar", is the first reserved id the sequence reaches.
+	it('skips a reserved id instead of assigning it', () => {
+		expect(nextId(stateWith(['failure']), flowWith(['ar']))).toBe('at')
+	})
 })

frontend/src/lib/components/flows/flowModuleNextId.ts

@@ -25,13 +25,23 @@ function autoIdNumber(key: string): number | undefined {
 
 // Computes the next available id
 export function nextId(flowState: FlowState, fullFlow: OpenFlow): string {
-	const allIds = dfs(fullFlow.value.modules, (fm) => fm.id)
+	const allKeys = dfs(fullFlow.value.modules, (fm) => fm.id).concat(Object.keys(flowState))
+	const takenIds = new Set(allKeys)
 
-	const max = allIds.concat(Object.keys(flowState)).reduce((acc, key) => {
+	const max = allKeys.reduce((acc, key) => {
 		const num = autoIdNumber(key)
 		return num === undefined ? acc : Math.max(acc, num + 1)
 	}, 0)
-	return numberToChars(max)
+
+	// A reserved id (e.g. "as", after "ar") never raises `max`, so assigning
+	// numberToChars(max) when it is reserved would make every later call return
+	// it again; skip forward to a free, allowed id instead.
+	let candidate = max
+	let id = numberToChars(candidate)
+	while (reservedIds.has(id) || takenIds.has(id)) {
+		id = numberToChars(++candidate)
+	}
+	return id
 }
 
 // Computes a copy id like "a2", "a3", etc. based on the original id