Salvages JSON envelopes cut mid-string by upstream size caps: the intact prefix is recovered, compressed via the normal routing path, and re-emitted as valid JSON with a _ctxzip_note telling the model the tail was destroyed upstream (not offloaded — re-run the tool). Ambiguous cuts (outside a string value) still fail open. Found live: a 108KB kubectl -o json envelope was hard-truncated by the runtime before compression, breaking the JSON and defeating the envelope path entirely.