fix: reject invalid and duplicate Work writes

agent_platform/runtime/loop.py

@@ -1,6 +1,8 @@
 from __future__ import annotations
 
+import ast
 import asyncio
+import hashlib
 import html
 import json
 import re
@@ -319,6 +321,32 @@ def normalize_tool_arguments(name: str, arguments: dict[str, Any]) -> dict[str,
     return {**arguments, "content": normalized}
 
 
+def write_call_fingerprint(name: str, arguments: dict[str, Any]) -> str | None:
+    if name != "write_file":
+        return None
+    path = arguments.get("path")
+    content = arguments.get("content")
+    if not isinstance(path, str) or not isinstance(content, str):
+        return None
+    digest = hashlib.sha256(content.encode("utf-8")).hexdigest()
+    return f"{PurePosixPath(path)}\0{digest}"
+
+
+def python_source_error(arguments: dict[str, Any]) -> str | None:
+    path = arguments.get("path")
+    content = arguments.get("content")
+    if not isinstance(path, str) or not isinstance(content, str):
+        return None
+    if PurePosixPath(path).suffix.lower() != ".py":
+        return None
+    try:
+        ast.parse(content, filename=path)
+    except SyntaxError as exc:
+        location = f"line {exc.lineno}" if exc.lineno else "unknown line"
+        return f"{exc.msg} ({location})"
+    return None
+
+
 def is_substantive_execution(name: str, arguments: dict[str, Any]) -> bool:
     if name == "start_process":
         return True
@@ -466,6 +494,7 @@ class AgentLoop:
         successful_executions = 0
         unresolved_execution_failure: str | None = None
         failed_execution_revisions: dict[str, int] = {}
+        successful_write_fingerprints: set[str] = set()
         consecutive_checkpoint_rejections = 0
         for iteration in range(max_iterations):
             await recorder.emit(
@@ -544,6 +573,7 @@ class AgentLoop:
             blocked_call_reasons: dict[str, str] = {}
             batch_mutation_epoch = 0
             batch_execution_epochs: dict[str, int] = {}
+            batch_write_fingerprints: set[str] = set()
             for call in tool_calls:
                 function = call.get("function") or {}
                 name = str(function.get("name", ""))
@@ -551,12 +581,22 @@ class AgentLoop:
                     arguments = json.loads(function.get("arguments") or "{}")
                 except json.JSONDecodeError:
                     arguments = {}
+                if isinstance(arguments, dict):
+                    arguments = normalize_tool_arguments(name, arguments)
                 if name in MUTATION_TOOLS:
                     batch_mutation_epoch += 1
+                fingerprint = write_call_fingerprint(name, arguments) if isinstance(arguments, dict) else None
+                call_id = str(call.get("id") or "")
+                if fingerprint and (
+                    fingerprint in successful_write_fingerprints or fingerprint in batch_write_fingerprints
+                ):
+                    blocked_call_reasons[call_id] = "duplicate_write"
+                    continue
+                if fingerprint:
+                    batch_write_fingerprints.add(fingerprint)
                 key = execution_call_key(name, arguments) if isinstance(arguments, dict) else None
                 if not key:
                     continue
-                call_id = str(call.get("id") or "")
                 if failed_execution_revisions.get(key) == mutation_count and batch_mutation_epoch == 0:
                     blocked_call_reasons[call_id] = "failed_retry"
                 elif batch_execution_epochs.get(key) == batch_mutation_epoch:
@@ -580,10 +620,15 @@ class AgentLoop:
                     arguments = json.loads(function.get("arguments") or "{}")
                 except json.JSONDecodeError:
                     arguments = {}
+                if isinstance(arguments, dict):
+                    arguments = normalize_tool_arguments(name, arguments)
                 if result.get("ok", False):
                     successful_tools += 1
                     if name in MUTATION_TOOLS:
                         mutation_count += 1
+                    fingerprint = write_call_fingerprint(name, arguments) if isinstance(arguments, dict) else None
+                    if fingerprint:
+                        successful_write_fingerprints.add(fingerprint)
                     elif name in VERIFICATION_TOOLS and mutation_count:
                         verified_mutation = mutation_count
                     if is_substantive_execution(name, arguments):
@@ -721,6 +766,15 @@ class AgentLoop:
         )
         if "__parse_error__" in arguments:
             result = {"ok": False, "error": arguments["__parse_error__"]}
+        elif blocked_reason == "duplicate_write":
+            result = {
+                "ok": False,
+                "policy_duplicate": True,
+                "error": (
+                    "Execution policy skipped this write because the same path and identical content were "
+                    "already written in this run. Make a real change before writing again."
+                ),
+            }
         elif blocked_reason == "batch_duplicate":
             result = {
                 "ok": False,
@@ -739,6 +793,14 @@ class AgentLoop:
                     "a materially different diagnostic command."
                 ),
             }
+        elif syntax_error := python_source_error(arguments):
+            result = {
+                "ok": False,
+                "error": (
+                    "Refused to write invalid complete Python source. "
+                    f"Fix the content and call write_file again: {syntax_error}"
+                ),
+            }
         elif name not in TOOL_METADATA:
             result = {"ok": False, "error": f"Unknown tool: {name}"}
         elif read_only and name not in READ_ONLY_TOOL_NAMES: