session-memory: Phase 4 Measure — baseline, effectiveness, trend (WP-0009)

Closes the loop. metrics.py: fleet metrics (infra-overhead share, error rate,
schema-thrash, token percentiles, success) + persisted baseline trend. effect.py:
before/after per-pattern effectiveness with an improved verdict per metric.
measure entrypoint with trend + --since effectiveness + JSON. Recorded pre-fix
baseline: 27 sessions, overhead median 11.7%, error rate 0.96, schema-thrash 8.
13 new tests; suite 139/139. Capture->Detect->Curate->Distribute->Measure complete.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_measure_entrypoint.py

@@ -0,0 +1,79 @@
+"""Measure entrypoint tests (WP-0009 T03)."""
+
+import json
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from session_memory.core.store import Store  # noqa: E402
+from session_memory.measure.__main__ import main, real_digests  # noqa: E402
+from session_memory.measure.metrics import load_baselines  # noqa: E402
+
+
+def _digest(uid, ts, tools=None):
+    return {
+        "session_uid": uid, "flavor": "claude", "repo": "agentic-resources",
+        "outcome": "success", "started_at": ts,
+        "cost": {"input_tokens": 100, "output_tokens": 10},
+        "event_count": 40, "first_prompt": "Implement the measure entrypoint cleanly",
+        "tool_histogram": tools or {"Bash": 20, "Edit": 12, "Read": 8},
+        "error_snippets": [],
+    }
+
+
+def _write_config(tmp_path) -> str:
+    store = tmp_path / ".store"
+    toml = tmp_path / "config.toml"
+    toml.write_text(
+        f'[store]\ndb_path = "{store / "m.db"}"\nblob_dir = "{store / "blobs"}"\n'
+        f'cursor = "{store / "c.json"}"\n'
+        f'[measure]\nbaselines = "{tmp_path / "baselines.jsonl"}"\n')
+    return str(toml), str(store)
+
+
+def _seed(store_dir):
+    st = Store(os.path.join(store_dir, "m.db"), os.path.join(store_dir, "blobs"))
+    st.write_digest("claude:a", _digest("claude:a", "2026-06-01"))
+    st.write_digest("claude:b", _digest("claude:b", "2026-06-10",
+                                        tools={"mcp__state-hub__x": 18, "Bash": 8, "Edit": 4}))
+    st.close()
+
+
+def test_real_digests_filters_and_loads(tmp_path):
+    cfg_path, store_dir = _write_config(tmp_path)
+    _seed(store_dir)
+    from session_memory.ingest import load_config
+    digs = real_digests(load_config(cfg_path))
+    assert len(digs) == 2
+
+
+def test_main_writes_baseline_and_reports(tmp_path, capsys):
+    cfg_path, store_dir = _write_config(tmp_path)
+    _seed(store_dir)
+    rc = main(["--config", cfg_path, "--label", "first"])
+    assert rc == 0
+    out = capsys.readouterr().out
+    assert "Fleet metrics" in out
+    rows = load_baselines(str(tmp_path / "baselines.jsonl"))
+    assert len(rows) == 1 and rows[0]["label"] == "first"
+
+
+def test_main_no_save_and_json(tmp_path, capsys):
+    cfg_path, store_dir = _write_config(tmp_path)
+    _seed(store_dir)
+    rc = main(["--config", cfg_path, "--no-save", "--json"])
+    assert rc == 0
+    data = json.loads(capsys.readouterr().out)
+    assert data["current"]["n_sessions"] == 2
+    assert not os.path.exists(str(tmp_path / "baselines.jsonl"))
+
+
+def test_main_effectiveness_since(tmp_path, capsys):
+    cfg_path, store_dir = _write_config(tmp_path)
+    _seed(store_dir)
+    rc = main(["--config", cfg_path, "--no-save", "--since", "2026-06-05", "--json"])
+    assert rc == 0
+    data = json.loads(capsys.readouterr().out)
+    assert data["effectiveness"]["n_before"] == 1
+    assert data["effectiveness"]["n_after"] == 1