A wrapper around a write call documented that write as a merge. Called directly, with a partial payload, the raw endpoint underneath it did not merge anything: it replaced the stack’s entire stored set. Before trusting a partial write to land safely on top of existing data, the endpoint actually receiving that write needs to be checked directly.
What was measured
In one measured case, a wrapper layer’s own language described a write operation as a merge: a partial payload was expected to combine with what already existed. The raw endpoint underneath that wrapper was also reachable directly, and calling it that way with a partial payload didn’t merge anything. Reading the underlying function’s own source afterward showed why: it deletes the entire existing set of values first, then inserts only what the request body contains. A single variable sent this way replaced the stack’s entire stored set.
Why the wrapper’s word wasn’t evidence
Calling the raw endpoint directly bypasses the wrapper entirely, and inherits whatever the raw endpoint itself does with a partial payload. Checked that way, it did not merge: it deleted the stack’s existing set and inserted exactly what the request body contained. What was documented at one layer had to be checked again at the layer where the call actually landed.
What this doesn’t establish
This was one endpoint, in one tool, called once, with one kind of partial payload. Nothing here says whether other endpoints in the same tool behave the same way, or whether a full-replace write is particular to this one call. The record that this is drawn from doesn’t say, so neither claim is made here.
Checking before trusting a partial write
The check that generalizes from this one case: before relying on a partial write reaching a system safely, read what the endpoint actually receiving that write does with a payload that doesn’t include every field. Where that isn’t documented, a small test against disposable data is one way to check.
The night this came from, told as it happened, is Act 76: The partial write that wasn’t.