fix: improve filterFields heuristic and maxLines nullish check (DIS-145)

- filterFields now checks if any requested field matches a top-level key.
  If yes, picks from top level (handles Collection with array props like
  contracts, editors). If no match, treats as wrapper and filters array
  items (handles {nfts: [...], next: ...} responses).
- Changed maxLines guard from truthiness to != null so --max-lines 0 works.
- Added tests for objects with array properties and maxLines 0.

Co-Authored-By: Chris K <ckorhonen@gmail.com>

Author: devin-ai-integration[bot]

src/output.ts

@@ -27,7 +27,7 @@ export function formatOutput(data: unknown, format: OutputFormat): string {
     result = JSON.stringify(processed, null, 2)
   }
 
-  if (_outputOptions.maxLines) {
+  if (_outputOptions.maxLines != null) {
     result = truncateOutput(result, _outputOptions.maxLines)
   }
 
@@ -99,21 +99,23 @@ function filterFields(data: unknown, fields: string[]): unknown {
   }
   if (data && typeof data === "object") {
     const obj = data as Record<string, unknown>
-    const arrayKeys = Object.keys(obj).filter(k => Array.isArray(obj[k]))
-    if (arrayKeys.length > 0) {
-      const result: Record<string, unknown> = {}
-      for (const [key, value] of Object.entries(obj)) {
-        result[key] = Array.isArray(value)
-          ? value.map(item =>
-              item && typeof item === "object"
-                ? pickFields(item as Record<string, unknown>, fields)
-                : item,
-            )
-          : value
-      }
-      return result
+    const keys = Object.keys(obj)
+    const hasMatchingKey = fields.some(f => f in obj)
+    if (hasMatchingKey) {
+      return pickFields(obj, fields)
     }
-    return pickFields(obj, fields)
+    const result: Record<string, unknown> = {}
+    for (const key of keys) {
+      const value = obj[key]
+      result[key] = Array.isArray(value)
+        ? value.map(item =>
+            item && typeof item === "object"
+              ? pickFields(item as Record<string, unknown>, fields)
+              : item,
+          )
+        : value
+    }
+    return result
   }
   return data
 }

test/output.test.ts

@@ -132,6 +132,23 @@ describe("formatOutput", () => {
       expect(result).toEqual({ name: "test" })
     })
 
+    it("filters top-level fields on objects with array properties", () => {
+      setOutputOptions({ fields: ["name", "collection"] })
+      const data = {
+        name: "Cool Cats",
+        collection: "cool-cats",
+        description: "A cool collection",
+        contracts: [{ address: "0x1", chain: "ethereum" }],
+        editors: ["alice"],
+        fees: [{ fee: 250, recipient: "0x2", required: true }],
+      }
+      const result = JSON.parse(formatOutput(data, "json"))
+      expect(result).toEqual({
+        name: "Cool Cats",
+        collection: "cool-cats",
+      })
+    })
+
     it("returns primitives unchanged", () => {
       setOutputOptions({ fields: ["name"] })
       expect(formatOutput("hello", "json")).toBe('"hello"')
@@ -183,6 +200,13 @@ describe("formatOutput", () => {
       expect(lines).toHaveLength(3)
       expect(lines[2]).toMatch(/\.\.\. \(\d+ more lines?\)/)
     })
+
+    it("handles max-lines 0 by truncating all lines", () => {
+      setOutputOptions({ maxLines: 0 })
+      const data = { a: 1 }
+      const result = formatOutput(data, "json")
+      expect(result).toContain("... (3 more lines)")
+    })
   })
 
   describe("--fields and --max-lines combined", () => {