diff --git a/CHANGELOG.md b/CHANGELOG.md
index bb2ec56..7547442 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,13 @@ All notable changes to vouch are documented here. Format follows
 - console Dashboard view: 12-month activity calendar, last-30-days bars,
   hour-of-week heatmap, top actors and event mix, driven by `kb.activity`.
 
+### Fixed
+- the JSONL / HTTP `/rpc` envelope misreported lifecycle guard failures
+  (e.g. `kb.supersede` of a claim onto itself) as `internal_error` and
+  logged a full server-side traceback for what is a bad request —
+  `LifecycleError` now maps to `invalid_request` like `ProposalError`,
+  matching how the CLI already surfaces it.
+
 ## [1.2.2] — 2026-07-07
 
 ### Packaging
diff --git a/src/vouch/jsonl_server.py b/src/vouch/jsonl_server.py
index 43a1472..633e250 100644
--- a/src/vouch/jsonl_server.py
+++ b/src/vouch/jsonl_server.py
@@ -39,6 +39,7 @@
 from . import verify as verify_mod
 from .capabilities import capabilities as build_caps
 from .context import build_context_pack
+from .lifecycle import LifecycleError
 from .logging_config import configure_logging
 from .models import ProposalStatus
 from .page_filters import filter_pages
@@ -891,7 +892,12 @@ def handle_request(envelope: dict) -> dict:
             "id": req_id, "ok": False,
             "error": {"code": "missing_param", "message": str(e)},
         }
-    except (ValueError, ProposalError, ArtifactNotFoundError) as e:
+    except (ValueError, ProposalError, LifecycleError, ArtifactNotFoundError) as e:
+        # Caller-visible domain errors. LifecycleError belongs here like
+        # ProposalError does (both are RuntimeError subclasses the generic
+        # branch would otherwise misreport as internal_error): a lifecycle
+        # guard such as "a claim cannot supersede itself" is a bad request,
+        # not a server fault. The CLI already maps it via _cli_errors.
         return {
             "id": req_id, "ok": False,
             "error": {"code": "invalid_request", "message": str(e)},
diff --git a/tests/test_jsonl_server.py b/tests/test_jsonl_server.py
index dc1aa0a..a8e0652 100644
--- a/tests/test_jsonl_server.py
+++ b/tests/test_jsonl_server.py
@@ -248,3 +248,27 @@ def _boom(_params: dict) -> dict:
     assert resp["ok"] is False
     assert resp["error"]["code"] == "internal_error"
     assert "traceback" not in resp["error"]
+
+
+def test_jsonl_lifecycle_guard_maps_to_invalid_request(
+    store: KBStore, monkeypatch,
+) -> None:
+    """Lifecycle guards are caller conditions, not server faults.
+
+    `kb.supersede` of a claim onto itself raises LifecycleError, which the
+    envelope used to misreport as internal_error (and log a full server-side
+    traceback for what is a bad request). It must map to invalid_request,
+    exactly as the CLI already surfaces it via _cli_errors."""
+    monkeypatch.chdir(store.root)
+    src = store.put_source(b"e")
+    store.put_claim(Claim(id="c1", text="a durable claim", evidence=[src.id]))
+    resp = handle_request({
+        "id": "r1", "method": "kb.supersede",
+        "params": {"old_claim_id": "c1", "new_claim_id": "c1"},
+    })
+    assert resp["ok"] is False
+    assert resp["error"]["code"] == "invalid_request"
+    assert "cannot supersede itself" in resp["error"]["message"]
+    # the guard fired before any write — the claim is untouched
+    assert store.get_claim("c1").status.value == "working"
+    assert store.get_claim("c1").superseded_by is None