fix(frontend): address PR review feedback on flow layout

- Add max recursion depth guard (50) to layoutLevel to prevent stack
  overflow with malformed flow data
- Log swallowed decrossOpt error as console.debug for debuggability
- Initialize maxY to -Infinity for correctness with negative positions
- Fix indentation artifacts in graphBuilder data objects

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/lib/components/graph/compoundLayout.ts

@@ -166,7 +166,8 @@ function runSugiyama(
 				return [w + constants.gapH, h + constants.gapV] as readonly [number, number]
 			})
 		boxSize = layout(dag as any) as any
-	} catch {
+	} catch (e) {
+		console.debug('[compoundLayout] decrossOpt failed, falling back to decrossTwoLayer:', e)
 		const layout = sugiyama()
 			.decross(decrossTwoLayer())
 			.coord(coordCenter())
@@ -229,11 +230,14 @@ function runSugiyama(
  * 5. Run sugiyama on the simplified graph
  * 6. Expand wrapper positions back to absolute positions
  */
+const MAX_RECURSION_DEPTH = 50
+
 function layoutLevel(
 	nodeIds: string[],
 	allNodes: Map<string, LayoutNode>,
 	constants: LayoutConstants,
-	childrenMap: Map<string, string[]>
+	childrenMap: Map<string, string[]>,
+	depth: number = 0
 ): LayoutResult {
 	const positions = new Map<string, { x: number; y: number }>()
 	const nodeIdSet = new Set(nodeIds)
@@ -246,6 +250,19 @@ function layoutLevel(
 		}
 	}
 
+	if (depth >= MAX_RECURSION_DEPTH) {
+		console.warn('[compoundLayout] Max recursion depth reached, falling back to flat layout')
+		const flatNodes = nodeIds.map((id) => {
+			const n = allNodes.get(id)!
+			return { id, parentIds: (n.parentIds ?? []).filter((pid) => nodeIdSet.has(pid)) }
+		})
+		const result = runSugiyama(flatNodes, constants)
+		for (const [id, pos] of result.positions) {
+			positions.set(id, pos)
+		}
+		return { positions, bbox: { width: result.width, height: result.height }, contentMinX: 0 }
+	}
+
 	// Step 1: detect compound groups at this level
 	const groups = detectGroups(nodeIdSet, allNodes, childrenMap)
 
@@ -305,7 +322,7 @@ function layoutLevel(
 			const branchNodeIds = [branch.labelId, ...branch.innerIds]
 
 			// Find sub-groups within this branch
-			const result = layoutLevel(branchNodeIds, allNodes, constants, childrenMap)
+			const result = layoutLevel(branchNodeIds, allNodes, constants, childrenMap, depth + 1)
 
 			branchLayouts.push({
 				labelId: branch.labelId,
@@ -453,7 +470,7 @@ function layoutLevel(
 	let minX = Infinity
 	let maxX = -Infinity
 	let minY = Infinity
-	let maxY = 0
+	let maxY = -Infinity
 	for (const pos of positions.values()) {
 		minX = Math.min(minX, pos.x - constants.nodeWidth / 2)
 		maxX = Math.max(maxX, pos.x + constants.nodeWidth / 2)

frontend/src/lib/components/graph/graphBuilder.svelte.ts

@@ -650,7 +650,7 @@ export function graphBuilder(
 							const startNode: NodeLayout = {
 								id: `${module.id}-branch-0`,
 								data: {
-										id: module.id,
+									id: module.id,
 									branchIndex: -1,
 									eventHandlers: eventHandlers,
 									flowModuleState: extra.flowModuleStates?.[module.id],
@@ -675,7 +675,7 @@ export function graphBuilder(
 								const startNode: NodeLayout = {
 									id: `${module.id}-branch-${branchIndex}`,
 									data: {
-												label: defaultIfEmptyString(branch.summary, `Branch ${branchIndex + 1}`),
+										label: defaultIfEmptyString(branch.summary, `Branch ${branchIndex + 1}`),
 										id: module.id,
 										branchIndex: branchIndex,
 										eventHandlers: eventHandlers,
@@ -878,7 +878,7 @@ export function graphBuilder(
 							const startNode: NodeLayout = {
 								id: `${module.id}-branch-${branchIndex}`,
 								data: {
-										label: defaultIfEmptyString(branch.summary, 'Branch ' + (branchIndex + 1)),
+									label: defaultIfEmptyString(branch.summary, 'Branch ' + (branchIndex + 1)),
 									preLabel: branch.summary ? '' : branch.expr,
 									id: module.id,
 									branchIndex: branchIndex,
@@ -921,7 +921,7 @@ export function graphBuilder(
 							const startNode: NodeLayout = {
 								id: startId,
 								data: {
-										label: `Start of subflow ${idWithoutPrefix}`,
+									label: `Start of subflow ${idWithoutPrefix}`,
 									id: startId,
 									subflowId: module.id,
 									eventHandlers: eventHandlers,
@@ -949,7 +949,7 @@ export function graphBuilder(
 							const endNode: NodeLayout = {
 								id: endId,
 								data: {
-										label: `End of subflow ${idWithoutPrefix}`,
+									label: `End of subflow ${idWithoutPrefix}`,
 									id: endId,
 									subflowId: module.id,
 									eventHandlers: eventHandlers,