docs: describe read-line edit guard in tool playbook

src/plyngent/agent/directive_checkpoint.py

@@ -19,7 +19,8 @@ DEFAULT_DIRECTIVE_REMINDER_TEXT = """\
 Tool playbook still applies (see system). Hard constraints:
 - Prefer file tools over shell; several `run_command` calls may run in parallel; \
 use `run_command_batch` for ordered pipelines.
-- `edit_replace`: fix match / `max_replaces`; `read_file` with_lineno before `edit_lineno`.
+- `edit_replace`: fix match / `max_replaces`; `edit_lineno` edits only lines read via \
+`read_file(with_lineno=true)`, and line numbers reset after any file write.
 - Prefer `fetch` for HTTP(S); private/LAN hosts need human policy allow (not YOLO).
 - PTY secrets only via `ask_into_pty`; denylists and confirms still apply.
 - Todo stack: open items mean unfinished work.

src/plyngent/config/models.py

@@ -21,7 +21,9 @@ DEFAULT_TOOL_DIRECTIVES = """\
 fix `old_string` or `max_replaces`; shell workarounds rarely help.
 - `edit_replace` defaults to the first match; if remaining matches are reported, \
 raise `max_replaces` or narrow `old_string`.
-- Before `edit_lineno`, `read_file` with `with_lineno=true`.
+- `edit_lineno` edits only lines you read via `read_file(path, with_lineno=true)`; \
+re-read with line numbers after any `edit_*` / `write_file` / copy/move/delete, \
+since line numbers go stale.
 
 ### Commands
 - Prefer `run_command` / `run_command_batch` (argv, no shell) over `bash -c` or similar.

src/plyngent/tools/file/read.py

@@ -29,7 +29,8 @@ async def read_file(
 
     ``offset`` is 0-based line start; ``limit`` is max lines (None = rest of file).
     When ``with_lineno`` is true, each line is prefixed with its 1-based file line
-    number (``     N|…``), matching ``edit_lineno`` numbering.
+    number (``     N|…``), matching ``edit_lineno`` numbering, and those lines are
+    marked readable for ``edit_lineno`` this turn.
     """
     target = resolve_path(path)
     if not target.is_file():