core/tools: add per-turn guard requiring lineno read before edit_lineno

src/plyngent/agent/__init__.py

@@ -1,4 +1,8 @@
 from .chat import ChatAgent as ChatAgent
+from .chat import get_lineno_read_files as get_lineno_read_files
+from .chat import mark_lineno_read as mark_lineno_read
+from .chat import reset_lineno_tracker as reset_lineno_tracker
+from .chat import was_lineno_read as was_lineno_read
 from .compact import build_compacted_seed_messages as build_compacted_seed_messages
 from .compact import summarize_messages as summarize_messages
 from .events import AgentEvent as AgentEvent

src/plyngent/agent/chat.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from contextvars import ContextVar, Token
 from typing import TYPE_CHECKING
 
 from msgspec import UNSET
@@ -46,6 +47,44 @@ if TYPE_CHECKING:
     type LimitContinueHook = Callable[[str], bool | Awaitable[bool]]
 
 
+# Per-conversation tracking of files read with ``with_lineno=True``.
+# Set to a fresh ``set`` at the start of each user turn via
+# :func:`reset_lineno_tracker`; cleared after the assistant finishes.
+# Tool handlers read/write via :func:`get_lineno_read_files`.
+_lineno_read_files: ContextVar[set[str] | None] = ContextVar("_lineno_read_files", default=None)
+
+
+def reset_lineno_tracker() -> Token[set[str] | None]:
+    """Replace the tracker with a fresh empty set; return the previous token.
+
+    Call at the start of a new user turn. Restore with
+    ``_lineno_read_files.reset(token)`` when the turn completes.
+    """
+    return _lineno_read_files.set(set())
+
+
+def get_lineno_read_files() -> set[str]:
+    """Return the current turn's set of line-numbered file paths.
+
+    Returns an empty set when no turn is active (tools will reject edits).
+    """
+    val = _lineno_read_files.get()
+    return val if val is not None else set()
+
+
+def mark_lineno_read(path: str) -> None:
+    """Record that *path* was read with line numbers this turn."""
+    val = _lineno_read_files.get()
+    if val is not None:
+        val.add(path)
+
+
+def was_lineno_read(path: str) -> bool:
+    """Return True if *path* was read with line numbers this turn."""
+    val = _lineno_read_files.get()
+    return val is not None and path in val
+
+
 def incomplete_turn_user_text(messages: Sequence[AnyChatMessage]) -> str | None:
     """User text for an incomplete turn, if history can be retried.
 
@@ -484,6 +523,7 @@ class ChatAgent:
 
     async def run(self, user_text: str) -> AsyncIterator[AgentEvent]:
         """Append a user message (persist immediately), run the tool loop, yield events."""
+        _ = reset_lineno_tracker()
         self._ensure_system_prompt()
         user_msg = UserChatMessage(content=user_text)
         self.messages.append(user_msg)

src/plyngent/tools/file/edit_lineno.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from typing import TYPE_CHECKING
 
-from plyngent.agent import ToolTag, tool
+from plyngent.agent import ToolTag, tool, was_lineno_read
 from plyngent.tools.workspace import resolve_path
 
 if TYPE_CHECKING:
@@ -85,6 +85,11 @@ async def edit_lineno(path: str, start_line: int, end_line: int, new_content: st
     target = resolve_path(path)
     if not target.is_file():
         return f"error: not a file: {path}"
+    if not was_lineno_read(str(target)):
+        return (
+            f"error: read {path!r} first with read_file(path, with_lineno=true) "
+            "to get correct line numbers"
+        )
 
     text = target.read_text(encoding="utf-8", errors="replace")
     lines = text.splitlines(keepends=True)

src/plyngent/tools/file/read.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from plyngent.agent import ToolTag, tool
+from plyngent.agent import ToolTag, mark_lineno_read, tool
 from plyngent.tools.workspace import resolve_path
 
 _LINENO_WIDTH = 6
@@ -44,5 +44,6 @@ async def read_file(
         return ""
     slice_lines = lines[start:end]
     if with_lineno:
+        mark_lineno_read(str(target))
         return _format_with_lineno(slice_lines, start_lineno=start + 1)
     return "".join(slice_lines)