diff --git a/strix/tools/reporting/tool.py b/strix/tools/reporting/tool.py
index c2a6abf7..164dd3af 100644
--- a/strix/tools/reporting/tool.py
+++ b/strix/tools/reporting/tool.py
@@ -2539,6 +2539,54 @@ def _sandbox_session(ctx: RunContextWrapper) -> Any:
     return inner.get("sandbox_session")
 
 
+def _entry_kind(entry: Any) -> str:
+    kind = getattr(entry, "kind", None)
+    if kind is None:
+        return "file"
+    value = getattr(kind, "value", kind)
+    return str(value).lower()
+
+
+def _entry_matches_path(entry: Any, path: str) -> bool:
+    entry_path = str(getattr(entry, "path", "") or "")
+    if not entry_path:
+        return False
+    wanted = PurePosixPath(path)
+    listed = PurePosixPath(entry_path)
+    return entry_path in {path, wanted.name} or listed.name == wanted.name
+
+
+async def _inspect_workspace_file(session: Any, path: str) -> str | None:
+    """Reject symlinks and oversized files before the sandbox read follows them."""
+    ls = getattr(session, "ls", None)
+    if not callable(ls):
+        return None
+    parent = PurePosixPath(path).parent.as_posix()
+    try:
+        entries = await ls(Path(parent))
+    except Exception as exc:
+        logger.exception("export_markdown_report ls failed")
+        return f"Failed to inspect '{path}' in the sandbox: {exc!s}"
+    entry = next((item for item in entries or [] if _entry_matches_path(item, path)), None)
+    if entry is None:
+        return f"Markdown file not found: {path}"
+    return _reject_workspace_entry(path, entry)
+
+
+def _reject_workspace_entry(path: str, entry: Any) -> str | None:
+    kind = _entry_kind(entry)
+    if kind == "symlink":
+        return f"'{path}' is a symlink; export a regular markdown file inside /workspace"
+    if kind != "file":
+        return f"'{path}' is not a regular markdown file"
+    size = getattr(entry, "size", None)
+    if isinstance(size, int) and size <= 0:
+        return f"Markdown file is empty: {path}"
+    if isinstance(size, int) and size > _MAX_EXPORTED_REPORT_BYTES:
+        return f"Markdown file exceeds {_MAX_EXPORTED_REPORT_BYTES} bytes ({size} bytes)"
+    return None
+
+
 def _export_destination(
     ctx: RunContextWrapper, path: str
 ) -> tuple[Any, Path, str, str] | dict[str, Any]:
@@ -2563,7 +2611,33 @@ def _export_destination(
     return session, report_state.get_run_dir(), workspace_path, name
 
 
+def _read_limited_bytes(stream: Any) -> tuple[bytes | None, str | None]:
+    """Copy at most one extra byte past the export limit, then close ``stream``."""
+    limit = _MAX_EXPORTED_REPORT_BYTES + 1
+    try:
+        chunks: list[bytes] = []
+        remaining = limit
+        while remaining > 0:
+            chunk = stream.read(remaining)
+            if not chunk:
+                break
+            if isinstance(chunk, str):
+                chunk = chunk.encode("utf-8")
+            if not isinstance(chunk, bytes | bytearray):
+                return None, "sandbox read did not return file bytes"
+            chunks.append(bytes(chunk))
+            remaining -= len(chunk)
+        return b"".join(chunks), None
+    finally:
+        close = getattr(stream, "close", None)
+        if callable(close):
+            close()
+
+
 async def _read_workspace_markdown(session: Any, path: str) -> tuple[bytes | None, str | None]:
+    inspect_error = await _inspect_workspace_file(session, path)
+    if inspect_error is not None:
+        return None, inspect_error
     try:
         stream = await session.read(Path(path))
     except FileNotFoundError:
@@ -2571,17 +2645,14 @@ async def _read_workspace_markdown(session: Any, path: str) -> tuple[bytes | Non
     except Exception as exc:
         logger.exception("export_markdown_report read failed")
         return None, f"Failed to read '{path}' from the sandbox: {exc!s}"
-    try:
-        data = stream.read()
-    finally:
-        close = getattr(stream, "close", None)
-        if callable(close):
-            close()
-    if isinstance(data, str):
-        return data.encode("utf-8"), None
-    if isinstance(data, bytes | bytearray):
-        return bytes(data), None
-    return None, "sandbox read did not return file bytes"
+    data, read_error = _read_limited_bytes(stream)
+    if data is None:
+        return None, read_error
+    if len(data) > _MAX_EXPORTED_REPORT_BYTES:
+        return None, (
+            f"Markdown file exceeds {_MAX_EXPORTED_REPORT_BYTES} bytes ({len(data)} bytes)"
+        )
+    return data, None
 
 
 def _markdown_text(path: str, payload: bytes) -> tuple[str | None, str | None]:
@@ -2605,6 +2676,15 @@ async def _export_markdown_report(ctx: RunContextWrapper, path: str) -> dict[str
     if isinstance(ready, dict):
         return ready
     session, run_dir, workspace_path, name = ready
+    destination = run_dir / name
+    if destination.exists():
+        return {
+            "success": False,
+            "error": (
+                f"'{name}' already exists in the host run directory; "
+                "choose another markdown filename"
+            ),
+        }
 
     payload, read_error = await _read_workspace_markdown(session, workspace_path)
     if payload is None:
@@ -2613,7 +2693,6 @@ async def _export_markdown_report(ctx: RunContextWrapper, path: str) -> dict[str
     if text is None:
         return {"success": False, "error": text_error}
 
-    destination = run_dir / name
     try:
         atomic_write_text(destination, text)
     except OSError as exc:
diff --git a/tests/test_export_markdown_report.py b/tests/test_export_markdown_report.py
index ae16cf89..e600caf1 100644
--- a/tests/test_export_markdown_report.py
+++ b/tests/test_export_markdown_report.py
@@ -4,31 +4,83 @@ from __future__ import annotations
 
 import io
 import json
-from collections.abc import Iterator
 from typing import TYPE_CHECKING, Any
 
 import pytest
+from agents.sandbox.files import EntryKind, FileEntry
+from agents.sandbox.types import Permissions
 from agents.tool_context import ToolContext
 
 from strix.report.state import ReportState, set_global_report_state
-from strix.tools.reporting.tool import export_markdown_report
+from strix.tools.reporting.tool import _MAX_EXPORTED_REPORT_BYTES, export_markdown_report
 
 
 if TYPE_CHECKING:
+    from collections.abc import Iterator
     from pathlib import Path
 
 
+def _file_entry(path: str, payload: bytes, *, kind: EntryKind = EntryKind.FILE) -> FileEntry:
+    return FileEntry(
+        path=path,
+        permissions=Permissions.from_mode(0o100644),
+        owner="root",
+        group="root",
+        size=len(payload),
+        kind=kind,
+    )
+
+
+class _SimpleEntry:
+    def __init__(self, path: str, *, kind: str = "file", size: int | None = None) -> None:
+        self.path = path
+        self.kind = kind
+        if size is not None:
+            self.size = size
+
+
 class _Sandbox:
-    def __init__(self, files: dict[str, bytes]) -> None:
+    def __init__(
+        self,
+        files: dict[str, bytes],
+        *,
+        kinds: dict[str, EntryKind] | None = None,
+        listed: dict[str, object] | None = None,
+    ) -> None:
         self.files = files
+        self.kinds = kinds or {}
+        self.listed = listed or {}
         self.reads: list[str] = []
+        self.bytes_read = 0
+
+    async def ls(self, path: Path) -> list[object]:
+        parent = path.as_posix().rstrip("/") or "/"
+        entries: list[object] = []
+        for file_path, payload in self.files.items():
+            if file_path.rsplit("/", 1)[0] == parent:
+                entries.append(
+                    self.listed.get(file_path)
+                    or _file_entry(
+                        file_path, payload, kind=self.kinds.get(file_path, EntryKind.FILE)
+                    )
+                )
+        return entries
 
     async def read(self, path: Path) -> io.BytesIO:
         self.reads.append(path.as_posix())
         payload = self.files.get(path.as_posix())
         if payload is None:
             raise FileNotFoundError(path.as_posix())
-        return io.BytesIO(payload)
+
+        sandbox = self
+
+        class _CountedBytes(io.BytesIO):
+            def read(self, size: int | None = -1) -> bytes:
+                chunk = super().read(-1 if size is None else size)
+                sandbox.bytes_read += len(chunk)
+                return chunk
+
+        return _CountedBytes(payload)
 
 
 @pytest.fixture
@@ -97,3 +149,66 @@ async def test_rejects_paths_outside_a_named_workspace_markdown_file(
     assert sandbox.reads == []
     assert not (report_state.get_run_dir() / "report.md").exists()
     assert not (report_state.get_run_dir() / "penetration_test_report.md").exists()
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    ("payload", "kind", "match"),
+    [
+        (b"", EntryKind.FILE, "empty"),
+        (b"# Findings\n\x00hidden\n", EntryKind.FILE, "markdown text file"),
+        (b"\xff\xfe# Findings\n", EntryKind.FILE, "UTF-8"),
+        (b"x" * (_MAX_EXPORTED_REPORT_BYTES + 1), EntryKind.FILE, "exceeds"),
+        (b"# Findings\n", EntryKind.SYMLINK, "symlink"),
+    ],
+)
+async def test_rejects_empty_invalid_oversized_and_symlink_reports(
+    report_state: ReportState,
+    payload: bytes,
+    kind: EntryKind,
+    match: str,
+) -> None:
+    sandbox = _Sandbox({"/workspace/report.md": payload}, kinds={"/workspace/report.md": kind})
+
+    result = await _export({"sandbox_session": sandbox}, "/workspace/report.md")
+
+    assert result["success"] is False
+    assert match in result["error"]
+    assert not (report_state.get_run_dir() / "report.md").exists()
+    if kind is EntryKind.SYMLINK or match in {"empty", "exceeds"}:
+        assert sandbox.reads == []
+    if match == "exceeds":
+        assert sandbox.bytes_read == 0
+
+
+@pytest.mark.asyncio
+async def test_size_limit_stops_the_sandbox_read_after_one_extra_byte(
+    report_state: ReportState,
+) -> None:
+    oversized = b"x" * (_MAX_EXPORTED_REPORT_BYTES + 64)
+    sandbox = _Sandbox(
+        {"/workspace/report.md": oversized},
+        listed={"/workspace/report.md": _SimpleEntry("/workspace/report.md")},
+    )
+
+    result = await _export({"sandbox_session": sandbox}, "/workspace/report.md")
+
+    assert result["success"] is False
+    assert "exceeds" in result["error"]
+    assert sandbox.bytes_read == _MAX_EXPORTED_REPORT_BYTES + 1
+    assert not (report_state.get_run_dir() / "report.md").exists()
+
+
+@pytest.mark.asyncio
+async def test_same_named_exports_do_not_overwrite_an_existing_report(
+    report_state: ReportState,
+) -> None:
+    run_dir = report_state.get_run_dir()
+    (run_dir / "report.md").write_text("# first\n", encoding="utf-8")
+    sandbox = _Sandbox({"/workspace/notes/report.md": b"# second\n"})
+
+    result = await _export({"sandbox_session": sandbox}, "/workspace/notes/report.md")
+
+    assert result["success"] is False
+    assert "already exists" in result["error"]
+    assert (run_dir / "report.md").read_text(encoding="utf-8") == "# first\n"