fix: inject longTermBackground into memory prompt (#1734)

The format_memory_for_injection function only processed recentMonths and
earlierContext from the history section, silently dropping longTermBackground.

The LLM writes longTermBackground correctly and it persists to memory.json,
but it was never injected into the system prompt — making the user's
long-term background invisible to the AI.

Add the missing field handling and a regression test.

Co-authored-by: ppyt <14163465+ppyt@users.noreply.github.com>

backend/packages/harness/deerflow/agents/memory/prompt.py

@@ -246,6 +246,10 @@ def format_memory_for_injection(memory_data: dict[str, Any], max_tokens: int = 2
         if earlier.get("summary"):
             history_sections.append(f"Earlier: {earlier['summary']}")
 
+        background = history_data.get("longTermBackground", {})
+        if background.get("summary"):
+            history_sections.append(f"Background: {background['summary']}")
+
         if history_sections:
             sections.append("History:\n" + "\n".join(f"- {s}" for s in history_sections))
 

backend/tests/test_memory_prompt_injection.py

@@ -154,3 +154,22 @@ def test_format_memory_renders_correction_without_source_error_normally() -> Non
 
     assert "Use make dev for local development." in result
     assert "avoid:" not in result
+
+
+def test_format_memory_includes_long_term_background() -> None:
+    """longTermBackground in history must be injected into the prompt."""
+    memory_data = {
+        "user": {},
+        "history": {
+            "recentMonths": {"summary": "Recent activity summary"},
+            "earlierContext": {"summary": "Earlier context summary"},
+            "longTermBackground": {"summary": "Core expertise in distributed systems"},
+        },
+        "facts": [],
+    }
+
+    result = format_memory_for_injection(memory_data, max_tokens=2000)
+
+    assert "Background: Core expertise in distributed systems" in result
+    assert "Recent: Recent activity summary" in result
+    assert "Earlier: Earlier context summary" in result