diff --git a/tests/test_is_error_persistence.py b/tests/test_is_error_persistence.py
new file mode 100644
index 00000000..fc9528b4
--- /dev/null
+++ b/tests/test_is_error_persistence.py
@@ -0,0 +1,60 @@
+"""is_error persistence (canonical-trajectory storage cut #5, sub-commit 1).
+
+Tool-result error state used to be an in-memory-only message key; it is now a
+persisted `conversations.is_error` column so a reload preserves it.  These exercise
+the round-trip on an ephemeral backend (`_schema` create_all → save → SELECT →
+reconstruct); the actual `upgrade()` path is covered by test_migration_060.py.
+"""
+
+from __future__ import annotations
+
+import json
+from typing import Any
+
+_TC = json.dumps([{"id": "c1", "type": "function", "function": {"name": "x", "arguments": "{}"}}])
+
+
+def test_tool_is_error_persists(backend: Any) -> None:
+    ws = "ws-iserr-1"
+    backend.save_message(ws, "user", "do it")
+    backend.save_message(ws, "assistant", "", tool_calls=_TC)
+    backend.save_message(ws, "tool", "boom", tool_call_id="c1", is_error=True)
+    tool = next(m for m in backend.load_messages(ws, repair=False) if m["role"] == "tool")
+    assert tool.get("is_error") is True
+
+
+def test_tool_without_error_has_no_flag(backend: Any) -> None:
+    ws = "ws-iserr-2"
+    backend.save_message(ws, "tool", "ok", tool_call_id="c1")
+    tool = next(m for m in backend.load_messages(ws, repair=False) if m["role"] == "tool")
+    # Only set when True (matches the in-memory convention; consumers use .get()).
+    assert "is_error" not in tool
+
+
+def test_non_tool_rows_never_carry_is_error(backend: Any) -> None:
+    ws = "ws-iserr-4"
+    backend.save_message(ws, "user", "hi")
+    backend.save_message(ws, "assistant", "hello")
+    msgs = backend.load_messages(ws, repair=False)
+    assert all("is_error" not in m for m in msgs)
+
+
+def test_bulk_preserves_is_error(backend: Any) -> None:
+    ws = "ws-iserr-3"
+    backend.save_messages_bulk(
+        [
+            {
+                "ws_id": ws,
+                "role": "tool",
+                "content": "boom",
+                "tool_call_id": "c1",
+                "is_error": True,
+            },
+            {"ws_id": ws, "role": "tool", "content": "ok", "tool_call_id": "c2"},
+        ]
+    )
+    by_id = {
+        m["tool_call_id"]: m for m in backend.load_messages(ws, repair=False) if m["role"] == "tool"
+    }
+    assert by_id["c1"].get("is_error") is True
+    assert "is_error" not in by_id["c2"]
diff --git a/turnstone/core/memory.py b/turnstone/core/memory.py
index 04515e73..8859481b 100644
--- a/turnstone/core/memory.py
+++ b/turnstone/core/memory.py
@@ -43,6 +43,7 @@ def save_message(
     tool_calls: str | None = None,
     source: str | None = None,
     event_id: int | None = None,
+    is_error: bool = False,
 ) -> int:
     """Log a message to the conversations table.
 
@@ -69,6 +70,7 @@ def save_message(
             tool_calls=tool_calls,
             source=source,
             event_id=event_id,
+            is_error=is_error,
         )
     except Exception:
         log.warning("Failed to save message for ws=%s role=%s", ws_id, role, exc_info=True)
diff --git a/turnstone/core/session.py b/turnstone/core/session.py
index 2cef9184..7e995dd0 100644
--- a/turnstone/core/session.py
+++ b/turnstone/core/session.py
@@ -2590,6 +2590,7 @@ class ChatSession:
                         "tool_calls": tc_json,
                         "provider_data": pd_str,
                         "source": src if isinstance(src, str) and src else None,
+                        "is_error": bool(msg.get("is_error", False)),
                     }
                 )
             save_messages_bulk(bulk_rows)
@@ -4097,7 +4098,8 @@ class ChatSession:
                         "tool_call_id": tc_id,
                         "content": output,
                     }
-                    if self._tool_error_flags.pop(tc_id, False):
+                    tool_is_error = self._tool_error_flags.pop(tc_id, False)
+                    if tool_is_error:
                         tool_msg["is_error"] = True
                     self.messages.append(tool_msg)
 
@@ -4137,6 +4139,7 @@ class ChatSession:
                         _tname,
                         tool_call_id=tc_id,
                         event_id=self._ui_event_id(),
+                        is_error=tool_is_error,
                     )
 
                     # Accumulate this result's operator context (guard
@@ -4305,6 +4308,7 @@ class ChatSession:
                     func_name,
                     tool_call_id=tc_id,
                     event_id=self._ui_event_id(),
+                    is_error=True,
                 )
                 # Emit synthetic tool_result so live SSE listeners can
                 # complete the in-DOM tool batch — without this the
diff --git a/turnstone/core/storage/_postgresql.py b/turnstone/core/storage/_postgresql.py
index a9ec8f72..13c3932b 100644
--- a/turnstone/core/storage/_postgresql.py
+++ b/turnstone/core/storage/_postgresql.py
@@ -291,6 +291,7 @@ class PostgreSQLBackend:
         tool_calls: str | None = None,
         source: str | None = None,
         event_id: int | None = None,
+        is_error: bool = False,
     ) -> int:
         now = datetime.now(UTC).strftime("%Y-%m-%dT%H:%M:%S")
         content = sanitize_text(content)
@@ -310,6 +311,7 @@ class PostgreSQLBackend:
                     tool_calls=tool_calls,
                     _source=source,
                     event_id=event_id,
+                    is_error=is_error,
                 )
                 .returning(conversations.c.id)
             )
@@ -342,6 +344,7 @@ class PostgreSQLBackend:
                     ),
                     "tool_calls": row.get("tool_calls"),
                     "_source": sanitize_text(row.get("source")),
+                    "is_error": bool(row.get("is_error", False)),
                 }
             )
         with self._conn() as conn:
@@ -368,6 +371,7 @@ class PostgreSQLBackend:
                         conversations.c.tool_calls,
                         conversations.c._source,
                         conversations.c.event_id,
+                        conversations.c.is_error,
                     )
                     .where(conversations.c.ws_id == ws_id)
                     .order_by(conversations.c.id.desc())
@@ -386,6 +390,7 @@ class PostgreSQLBackend:
                         conversations.c.tool_calls,
                         conversations.c._source,
                         conversations.c.event_id,
+                        conversations.c.is_error,
                     )
                     .where(conversations.c.ws_id == ws_id)
                     .order_by(conversations.c.id)
diff --git a/turnstone/core/storage/_protocol.py b/turnstone/core/storage/_protocol.py
index c6685f0a..5893105f 100644
--- a/turnstone/core/storage/_protocol.py
+++ b/turnstone/core/storage/_protocol.py
@@ -159,6 +159,7 @@ class StorageBackend(Protocol):
         tool_calls: str | None = None,
         source: str | None = None,
         event_id: int | None = None,
+        is_error: bool = False,
     ) -> int:
         """Log a message to the conversations table.
 
diff --git a/turnstone/core/storage/_schema.py b/turnstone/core/storage/_schema.py
index ebec15d6..9e2d31ba 100644
--- a/turnstone/core/storage/_schema.py
+++ b/turnstone/core/storage/_schema.py
@@ -56,6 +56,11 @@ conversations = sa.Table(
     # stay NULL → cursor logic falls back to the snapshot floor.  See
     # migration 059.
     sa.Column("event_id", sa.BigInteger),
+    # Tool-result error flag (persisted; migration 060).  Set on ``tool`` rows
+    # whose tool raised or was cancelled, so a reload preserves the error state
+    # (history rendering + the Anthropic ``is_error`` result block) instead of
+    # re-deriving it from a text heuristic.  Non-tool rows are always False.
+    sa.Column("is_error", sa.Boolean, nullable=False, server_default=sa.false()),
 )
 
 sa.Index("idx_conversations_timestamp", conversations.c.timestamp)
diff --git a/turnstone/core/storage/_sqlite.py b/turnstone/core/storage/_sqlite.py
index 2352edbc..19b3e4eb 100644
--- a/turnstone/core/storage/_sqlite.py
+++ b/turnstone/core/storage/_sqlite.py
@@ -325,6 +325,7 @@ class SQLiteBackend:
         tool_calls: str | None = None,
         source: str | None = None,
         event_id: int | None = None,
+        is_error: bool = False,
     ) -> int:
         now = datetime.now(UTC).strftime("%Y-%m-%dT%H:%M:%S")
         content = sanitize_text(content)
@@ -344,6 +345,7 @@ class SQLiteBackend:
                     "tool_calls": tool_calls,
                     "_source": source,
                     "event_id": event_id,
+                    "is_error": is_error,
                 },
             )
             if result.lastrowid is None:
@@ -390,6 +392,7 @@ class SQLiteBackend:
                     ),
                     "tool_calls": row.get("tool_calls"),
                     "_source": sanitize_text(row.get("source")),
+                    "is_error": bool(row.get("is_error", False)),
                 }
             )
         with self._conn() as conn:
@@ -429,6 +432,7 @@ class SQLiteBackend:
                         conversations.c.tool_calls,
                         conversations.c._source,
                         conversations.c.event_id,
+                        conversations.c.is_error,
                     )
                     .where(conversations.c.ws_id == ws_id)
                     .order_by(conversations.c.id.desc())
@@ -447,6 +451,7 @@ class SQLiteBackend:
                         conversations.c.tool_calls,
                         conversations.c._source,
                         conversations.c.event_id,
+                        conversations.c.is_error,
                     )
                     .where(conversations.c.ws_id == ws_id)
                     .order_by(conversations.c.id)
diff --git a/turnstone/core/storage/_utils.py b/turnstone/core/storage/_utils.py
index e254e631..a67d864b 100644
--- a/turnstone/core/storage/_utils.py
+++ b/turnstone/core/storage/_utils.py
@@ -451,6 +451,9 @@ def reconstruct_messages(
         # compute the resume cursor + locate the in-flight-turn boundary.
         # Defensive length check keeps pre-event_id 8-tuple fixtures valid.
         event_id = row[8] if len(row) > 8 else None
+        # ``is_error`` (10th column, migration 060) rides last so the tuple
+        # positions above stay stable; legacy fixtures (≤9-tuples) default False.
+        is_error = bool(row[9]) if len(row) > 9 else False
 
         if role == "user":
             parts: list[dict[str, Any]] = []
@@ -502,6 +505,8 @@ def reconstruct_messages(
                 "tool_call_id": tc_id or "",
                 "content": content or "",
             }
+            if is_error:
+                tmsg["is_error"] = True
             if event_id is not None:
                 tmsg["_event_id"] = int(event_id)
             messages.append(tmsg)
diff --git a/turnstone/core/storage/migrations/versions/060_unwrap_tool_envelopes.py b/turnstone/core/storage/migrations/versions/060_unwrap_tool_envelopes.py
index 4904115c..0173a298 100644
--- a/turnstone/core/storage/migrations/versions/060_unwrap_tool_envelopes.py
+++ b/turnstone/core/storage/migrations/versions/060_unwrap_tool_envelopes.py
@@ -159,6 +159,11 @@ def upgrade() -> None:
     #     PostgreSQL (native ALTER) both work — see migration 027.
     with op.batch_alter_table("conversations") as batch_op:
         batch_op.drop_column("_reminders")
+        # Persist the tool-result error flag (was an in-memory-only message key);
+        # existing rows backfill to False via the server_default.
+        batch_op.add_column(
+            sa.Column("is_error", sa.Boolean, nullable=False, server_default=sa.false())
+        )
 
 
 def downgrade() -> None:
@@ -168,3 +173,4 @@ def downgrade() -> None:
     # re-added column is therefore always NULL.
     with op.batch_alter_table("conversations") as batch_op:
         batch_op.add_column(sa.Column("_reminders", sa.Text, nullable=True))
+        batch_op.drop_column("is_error")