fix(read): truncate long lines at 500 chars as documented

src/fastcontext/agent/tool/read.py

@@ -6,7 +6,7 @@
 from .tool import Tool
 
 MAX_LINE = 2000
-MAX_LINE_LENGTH = 2000
+MAX_LINE_LENGTH = 500
 
 
 class ReadTool(Tool):

tests/test_read_truncation.py

@@ -0,0 +1,32 @@
+import asyncio
+import json
+import tempfile
+from pathlib import Path
+
+from fastcontext.agent.tool.read import ReadTool
+
+
+def test_read_truncates_long_lines_at_500():
+    """read.md promises lines longer than 500 chars are truncated to 500 with
+    '...'. Verify the runtime honors that length."""
+    read = ReadTool()
+    with tempfile.TemporaryDirectory() as cwd:
+        p = Path(cwd) / "long.txt"
+        p.write_text("a" * 600 + "\n" + "short\n", encoding="utf-8")
+
+        out = asyncio.run(read.call(json.dumps({"path": str(p)}), cwd=cwd))
+
+        # Exactly 500 chars of the long line survive, with a "..." marker.
+        assert "a" * 500 in out
+        assert "a" * 501 not in out
+        assert "..." in out
+        # Short lines are passed through untouched.
+        assert "short" in out
+
+
+def test_read_doc_matches_truncation_length():
+    """The documented truncation length must match the implementation."""
+    from fastcontext.agent.tool.read import MAX_LINE_LENGTH
+
+    assert MAX_LINE_LENGTH == 500
+    assert "500 characters" in ReadTool().description