chore(agent-context): drop the dead single_agent memory-file prefix

Author: lfnothias

sources/utils/agent_context.py

@@ -9,7 +9,9 @@
 import json
 from pathlib import Path
 
-_AGENT_FILE_PREFIXES = ("task_", "single_agent")
+# Both factories save agent memory as ``task_{agent_name}.json``; the
+# single-agent run saves itself as ``task_single_agent.json``.
+_AGENT_FILE_PREFIX = "task_"
 
 
 def _final_input_tokens(steps: list) -> int:
@@ -54,7 +56,7 @@ def read_agent_context_lengths(memory_dir: str, workflow_uuid: str) -> list[int]
 
     lengths = []
     for path in sorted(run_memory.glob("*.json")):
-        if not path.name.startswith(_AGENT_FILE_PREFIXES):
+        if not path.name.startswith(_AGENT_FILE_PREFIX):
             continue
         try:
             steps = json.loads(path.read_text())

tests/context_dispersity_test.py

@@ -203,6 +203,17 @@ def test_reader_skips_unreadable_and_untokened_agents():
         assert read_agent_context_lengths(root, "uuid-1") == [10]
 
 
+def test_reader_includes_the_single_agent_memory_file():
+    """A single-agent run saves its memory as task_single_agent.json."""
+    with tempfile.TemporaryDirectory() as root:
+        uuid = "single_agent_20260101_abc123"
+        run = Path(root) / uuid
+        run.mkdir()
+        _write_agent(run, "task_single_agent.json", [{"token_usage": {"input_tokens": 77}}])
+
+        assert read_agent_context_lengths(root, uuid) == [77]
+
+
 def test_reader_returns_empty_for_missing_run():
     with tempfile.TemporaryDirectory() as root:
         assert read_agent_context_lengths(root, "absent") == []