diff --git a/agent/prompt_builder.py b/agent/prompt_builder.py
index 2569302882..6c975b0a6b 100644
--- a/agent/prompt_builder.py
+++ b/agent/prompt_builder.py
@@ -1576,14 +1576,32 @@ def _truncate_content(
         warnings.append(msg)
     head_chars = int(max_chars * CONTEXT_TRUNCATE_HEAD_RATIO)
     tail_chars = int(max_chars * CONTEXT_TRUNCATE_TAIL_RATIO)
+    omitted = _omitted_headings(content, head_chars, len(content) - tail_chars)
+    sections = f" Omitted sections: {'; '.join(omitted)}." if omitted else ""
     marker = (
         f"\n\n[...truncated {filename}: kept {head_chars}+{tail_chars} of {len(content)} chars. The middle is "
-        f"omitted — if you need the full instructions, read the complete file with the read_file tool: "
-        f"{read_path or filename}]\n\n"
+        f"omitted.{sections} If you need the full instructions, read the complete file with the read_file "
+        f"tool: {read_path or filename}]\n\n"
     )
     return content[:head_chars] + marker + content[-tail_chars:]
 
 
+def _omitted_headings(content: str, start: int, end: int, limit: int = 15) -> list:
+    """Markdown headings whose line starts inside ``content[start:end]``, so a truncation marker tells
+    the agent what it lost; ``#`` lines inside fenced code blocks are comments, not headings."""
+    import re
+
+    headings, offset, fenced = [], 0, False
+    for line in content.splitlines(keepends=True):
+        stripped = line.strip()
+        if stripped.startswith(("```", "~~~")):
+            fenced = not fenced
+        elif not fenced and start <= offset < end and re.match(r"#{1,6} \S", stripped):
+            headings.append(stripped.lstrip("#").strip())
+        offset += len(line)
+    return headings[:limit] + (["..."] if len(headings) > limit else [])
+
+
 def load_soul_md(context_length: Optional[int] = None, home_override: "Path | None" = None) -> Optional[str]:
     """SOUL.md from HERMES_HOME (identity slot #1), or None.
 
diff --git a/tests/agent/test_context_file_sources.py b/tests/agent/test_context_file_sources.py
index ef51e7cb97..24c4b4a22e 100644
--- a/tests/agent/test_context_file_sources.py
+++ b/tests/agent/test_context_file_sources.py
@@ -99,3 +99,17 @@ def test_truncated_and_suppressed_statuses_follow_the_builder(project, monkeypat
     assert "evil identity text" in prompt and "[BLOCKED: SOUL.md" not in prompt and "[BLOCKED: AGENTS.md" in prompt
     assert any("SOUL.md" in line and "review the file" in line
                for line in render_context_file_lines(list(entries.values())))
+
+
+def test_truncation_marker_names_the_omitted_sections_only():
+    from agent.prompt_builder import _truncate_content
+
+    pad = "word " * 400
+    content = (
+        f"# Kept head\n{pad}\n## Lost section\n{pad}\n```bash\n# a shell comment\n```\n"
+        f"### Lost subsection\n{pad}\n{pad}\n## Kept tail\nshort\n"
+    )
+    out = _truncate_content(content, "AGENTS.md", max_chars=2500, queue_warning=False)
+    marker = out[out.index("[...truncated"):out.index("]", out.index("[...truncated"))]
+    assert "Lost section; Lost subsection" in marker
+    assert "Kept head" not in marker and "Kept tail" not in marker and "shell comment" not in marker