crash

Nobody has claimed this yet.

```
[19871:0x261fab0] 9943111 ms: Mark-sweep 1425.6 (1470.6) -> 1425.6 (1470.6) MB, 2519.1 / 7.8 ms last resort

<--- JS stacktrace --->

==== JS stack trace =========================================

Security context: 0x10f09d0266a1
1: notFound [.../.nvm/versions/node/v7.10.0/lib/node_modules/dat/node_modules/append-tree/index.js:674] [pc=0x2ab92e0ec063](this=0x1f1940e08689 ,names=0x259447e76411 )
2: /* anonymous */ [.../.nvm/versions/node/v7.10.0/lib/node_modules/dat/node_modules/append-tree/index.js:110] [pc=0x2ab92e0ebe8b](this=0x1f1940e086...

FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory
1: node::Abort() [dat]
2: 0x12b82ac [dat]
3: v8::Utils::ReportOOMFailure(char const*, bool) [dat]
4: v8::internal::V8::FatalProcessOutOfMemory(char const*, bool) [dat]
5: v8::internal::Factory::NewTransitionArray(int) [dat]
6: v8::internal::TransitionArray::Insert(v8::internal::Handle, v8::internal::Handle, v8::internal::Handle, v8::internal::SimpleTransitionFlag) [dat]
7: v8::internal::Map::ShareDescriptor(v8::internal::Handle, v8::internal::Handle, v8::internal::Descriptor*) [dat] 8: v8::internal::Map::CopyAddDescriptor(v8::internal::Handle, v8::internal::Descriptor*, v8::internal::TransitionFlag) [dat]
9: v8::internal::Map::CopyWithField(v8::internal::Handle, v8::internal::Handle, v8::internal::Handle, v8::internal::PropertyAttributes, v8::internal::Representation, v8::internal::TransitionFlag) [dat]
10: v8::internal::Map::TransitionToDataProperty(v8::internal::Handle, v8::internal::Handle, v8::internal::Handle, v8::internal::PropertyAttributes, v8::internal::Object::StoreFromKeyed) [dat]
11: v8::internal::LookupIterator::PrepareTransitionToDataProperty(v8::internal::Handle, v8::internal::Handle, v8::internal::PropertyAttributes, v8::internal::Object::StoreFromKeyed) [dat]
12: v8::internal::StoreIC::LookupForWrite(v8::internal::LookupIterator*, v8::internal::Handle, v8::internal::Object::StoreFromKeyed) [dat]
13: v8::internal::StoreIC::UpdateCaches(v8::internal::LookupIterator*, v8::internal::Handle, v8::internal::Object::StoreFromKeyed) [dat]
14: v8::internal::StoreIC::Store(v8::internal::Handle, v8::internal::Handle, v8::internal::Handle, v8::internal::Object::StoreFromKeyed) [dat]
15: v8::internal::Runtime_StoreIC_Miss(int, v8::internal::Object**, v8::internal::Isolate*) [dat]
16: 0x2ab92dc043a7
Aborted
```

The report points to node_modules/append-tree/index.js:674, in notFound, with a Node.js heap-out-of-memory crash. Start by tracing that entry point and finding a reproducible input; done means the case no longer exhausts the heap and a regression test covers it.

Written by the indexing model from the issue text.