diff --git a/agent/agent_runtime_helpers.py b/agent/agent_runtime_helpers.py
index 062549ed7f..4a1e969e92 100644
--- a/agent/agent_runtime_helpers.py
+++ b/agent/agent_runtime_helpers.py
@@ -33,6 +33,7 @@ from pathlib import Path
 from typing import Any, Dict, List, Optional, Tuple
 
 from hermes_cli.timeouts import get_provider_request_timeout
+from agent.message_sanitization import _FULL_ARGS_LOG_BOUND
 from agent.prompt_builder import format_steer_marker
 from agent.tool_dispatch_helpers import _trajectory_normalize_msg, make_tool_result_message
 from agent.trajectory import convert_scratchpad_to_think
@@ -385,10 +386,19 @@ def sanitize_tool_call_arguments(
                 # itself becomes an orphan (#58168).
                 tool_call_id = _ra().AIAgent._get_tool_call_id_static(tool_call) or None
                 function_name = function.get("name", "?")
-                preview = arguments[:80]
+                # Log the FULL original argument string (bounded), not an
+                # 80-char preview: this branch is about to overwrite the
+                # only copy of these bytes in the transcript with "{}", and
+                # for a truncated write_file/patch call the destroyed
+                # arguments contain real user content (#80498 — streamed
+                # file content survived only as a log preview). A corrupted
+                # call is rare, so the oversized WARNING is a fair price for
+                # making the data recoverable from agent.log.
+                preview = arguments[:_FULL_ARGS_LOG_BOUND]
                 log.warning(
                     "Corrupted tool_call arguments repaired before request "
-                    "(session=%s, message_index=%s, tool_call_id=%s, function=%s, preview=%r)",
+                    "(session=%s, message_index=%s, tool_call_id=%s, function=%s, "
+                    "original_arguments=%r)",
                     session_id or "-",
                     message_index,
                     tool_call_id or "-",
diff --git a/agent/message_sanitization.py b/agent/message_sanitization.py
index dc4df3dd27..0fa7d95fff 100644
--- a/agent/message_sanitization.py
+++ b/agent/message_sanitization.py
@@ -183,6 +183,15 @@ def _escape_invalid_chars_in_json_strings(raw: str) -> str:
     return "".join(out)
 
 
+# When a repair is about to destroy the only copy of a tool call's original
+# argument bytes (rewriting them to "{}"), the WARNING log is the last
+# surviving copy of content that can hold real user data (#80498). Bound the
+# logged string at this size instead of a short preview so it stays
+# recoverable from agent.log without letting a pathological payload flood
+# the log.
+_FULL_ARGS_LOG_BOUND = 100_000
+
+
 def _repair_tool_call_arguments(raw_args: str, tool_name: str = "?") -> str:
     """Attempt to repair malformed tool_call argument JSON.
 
@@ -271,11 +280,15 @@ def _repair_tool_call_arguments(raw_args: str, tool_name: str = "?") -> str:
         pass
 
     # Last resort: replace with empty object so the API request doesn't
-    # crash the entire session.
+    # crash the entire session. Log the FULL original string (bounded) —
+    # for callers that discard the original (e.g. the pre-send transcript
+    # sanitizer), this WARNING is the last surviving copy of bytes that can
+    # contain real user content (#80498: a truncated write_file call's
+    # streamed file content).
     logger.warning(
         "Unrepairable tool_call arguments for %s — "
         "replaced with empty object (was: %s)",
-        tool_name, raw_stripped[:80],
+        tool_name, raw_stripped[:_FULL_ARGS_LOG_BOUND],
     )
     return "{}"