5b2: make the pipe escape terminate, cap the value a document fault echoes

src/adf/document.test.ts

@@ -19,6 +19,8 @@ test('names the check anything that is not a doc node failed', () => {
   assert.equal(fault(undefined), 'an ADF document is an object: found undefined')
   assert.equal(fault([]), 'an ADF document is an object: found an array')
   assert.equal(fault('doc'), 'an ADF document is an object: found "doc"')
+  assert.equal(fault('x'.repeat(200000)), `an ADF document is an object: found "${'x'.repeat(40)}…"`)
+  assert.equal(fault(function named(first: number, second: number) { return first + second }), 'an ADF document is an object: found a function')
   assert.equal(fault({ fields: { description: { type: 'doc', version: 1 } } }), 'an ADF document holds content, type and version alone: found the key fields')
   assert.equal(fault({ extra: 1, type: 'doc', version: 1 }), 'an ADF document holds content, type and version alone: found the key extra')
   assert.equal(fault({ version: 1 }), 'an ADF document holds type "doc": found no type field')

src/adf/document.ts

@@ -90,7 +90,8 @@ function isRecord(value: unknown): value is Record<string, unknown> {
 }
 
 function describe(value: unknown): string {
-  if (typeof value === 'string') return JSON.stringify(value)
+  if (typeof value === 'string') return JSON.stringify(value.length > 40 ? `${value.slice(0, 40)}…` : value)
+  if (typeof value === 'function') return 'a function'
   if (typeof value === 'object' && value !== null) return Array.isArray(value) ? 'an array' : 'an object'
   return String(value)
 }