diff --git a/lib/providers/anthropic.mjs b/lib/providers/anthropic.mjs
index 715e3a6..23feee6 100644
--- a/lib/providers/anthropic.mjs
+++ b/lib/providers/anthropic.mjs
@@ -1107,7 +1107,21 @@ async function* _spawnAndStream(irRequest, authContext, spawnImpl) {
   // Process close — safety net if no `result` event was emitted
   // (e.g. version drift where stream-json is not supported without -p).
   // Only throw on non-zero exit; zero exit with no result → emit synthetic stop.
-  if (exitCode !== 0 && !spawnTimedOut) {
+  //
+  // 2026-05-28 PR-B fold-in: when the spawn is sandbox-wrapped via /bin/sh -c
+  // '<bwrap-args> ... claude ...', the wrapping shell can exit with code
+  // `null` (signal-cleanup) even though the model completed and emitted the
+  // `result` event. resultEventSeen=true is the authoritative signal that
+  // the model finished successfully; an abnormal exit *after* that is just
+  // sandbox bookkeeping noise, not a real failure. Without this guard, the
+  // HTTP layer would receive a thrown ProviderError despite chunks having
+  // been yielded, and the response would come back with content:null.
+  //
+  // Live PI231 evidence (2026-05-28 commit 2864275 deploy):
+  //   stream NDJSON: delta(DIRECT_PROOF) → stop → close(null)
+  //   without this guard: ProviderError 'claude exit null' → empty response
+  //   with this guard:    chunks propagate normally, content arrives
+  if (exitCode !== 0 && !spawnTimedOut && !resultEventSeen) {
     const errMsg = accumulatedStderr.slice(0, 300) || `claude exit ${exitCode}`;
     throw new ProviderError(errMsg, 'SPAWN_FAILED');
   }