fix: avoid overwriting new file targets

Author: Eilen6316

prompts/file_patch_repair.md

@@ -30,9 +30,14 @@ markdown, prose, or shell commands. Use exactly this top-level shape:
 }}
 ```
 
-Do not use `--- /dev/null` for a target file that already exists; generate an
-update diff against the existing file. If the current file snapshot is present
-in the failure context, base the hunk context on that snapshot. If the failure
-mentions `expected=...` and `actual=...`, the previous hunk context is stale:
-use the `actual` line and the current snapshot as the source of truth, then
-return a new diff whose context lines exactly match the current file.
+Do not use `--- /dev/null` for a target file that already exists. If the
+original request asked to create a new file and the chosen filename is already
+taken, inspect the sibling directory with `list_dir` and return a create diff
+for a clear unused filename in that same directory. Do not update, overwrite, or
+rewrite the existing file unless the original request asked to edit/update that
+file. If the current file snapshot is present in the failure context and the
+user asked to update that existing file, base the hunk context on that snapshot.
+If the failure mentions `expected=...` and `actual=...`, the previous hunk
+context is stale: use the `actual` line and the current snapshot as the source
+of truth, then return a new diff whose context lines exactly match the current
+file.

prompts/planner.md

@@ -99,9 +99,11 @@ shown to the user before any file is changed. Return only this JSON object:
 ```
 
 For new files, use `--- /dev/null` and `+++ /absolute/or/relative/path` in the
-unified diff. If read-only tools show the target file already exists, generate
-an update diff with the existing path in both headers; never use `/dev/null` for
-an existing target. Do not apply the patch through shell commands; the graph
-applies FilePatchPlan after human confirmation. If a generated script needs
-executable permissions, use `permission_changes`; do not emit `chmod` as a shell
-command.
+unified diff. When the user asks to create a new file, first inspect the target
+directory; if your preferred filename already exists, choose a clear unused
+filename in the same directory instead of updating or overwriting the existing
+file. Only generate an update diff with the existing path in both headers when
+the user asked to edit/update that existing file. Do not apply the patch through
+shell commands; the graph applies FilePatchPlan after human confirmation. If a
+generated script needs executable permissions, use `permission_changes`; do not
+emit `chmod` as a shell command.

src/linuxagent/graph/file_patch_nodes.py

@@ -359,7 +359,7 @@ def _should_repair_patch_safety_failure(state: AgentState, safety: FilePatchSafe
 def _is_repairable_patch_error(reasons: str) -> bool:
     return (
         "unified diff context does not match target file" in reasons
-        or "target already exists; use an update diff instead of a create diff" in reasons
+        or "target already exists" in reasons
     )
 
 

src/linuxagent/plans/file_patch.py

@@ -282,7 +282,8 @@ def _planned_file_update(patch: _FilePatch) -> _PlannedFileUpdate:
     target = _target_path(patch)
     if patch.old_path == "/dev/null" and target.exists():
         raise FilePatchApplyError(
-            "target already exists; use an update diff instead of a create diff",
+            "target already exists; create requests must choose an unused filename, "
+            "while edit requests must use an update diff",
             path=target,
         )
     old_lines = _read_lines(target)

tests/unit/graph/test_agent_graph.py

@@ -522,6 +522,36 @@ async def test_graph_repairs_failed_file_patch_and_reconfirms(tmp_path) -> None:
     assert "analysis ok" in str(resumed["messages"][-1].content)
 
 
+async def test_graph_repairs_new_file_name_collision_with_unused_name(tmp_path) -> None:
+    existing = tmp_path / "disk_info.sh"
+    alternate = tmp_path / "disk_info_1.sh"
+    existing.write_text("#!/bin/sh\necho existing\n", encoding="utf-8")
+    first_plan = file_patch_plan_json(str(existing), "#!/bin/sh\necho disk\n")
+    repaired_plan = file_patch_plan_json(str(alternate), "#!/bin/sh\necho disk\n")
+    graph, _provider = _graph(tmp_path, [first_plan, repaired_plan, "analysis ok"])
+    config = {"configurable": {"thread_id": "new-file-collision"}}
+
+    await graph.ainvoke(
+        initial_state("create a new disk info shell script in tmp", source=CommandSource.USER),
+        config=config,
+    )
+    snapshot = await graph.aget_state(config)
+    interrupts = snapshot.tasks[0].interrupts
+
+    assert interrupts[0].value["type"] == "confirm_file_patch"
+    assert interrupts[0].value["repair_attempt"] == 1
+    assert str(alternate) in interrupts[0].value["files_changed"]
+    assert str(existing) not in interrupts[0].value["files_changed"]
+
+    resumed = await graph.ainvoke(
+        Command(resume={"decision": "yes", "latency_ms": 1}), config=config
+    )
+
+    assert existing.read_text(encoding="utf-8") == "#!/bin/sh\necho existing\n"
+    assert alternate.read_text(encoding="utf-8") == "#!/bin/sh\necho disk\n"
+    assert "analysis ok" in str(resumed["messages"][-1].content)
+
+
 async def test_graph_blocks_file_patch_outside_allow_roots(tmp_path) -> None:
     target = tmp_path / "blocked" / "demo.sh"
     graph, _provider = _graph(