session-memory: error-body mining into digest (WP-0006 T01)

build_digest now extracts normalized error fingerprints + samples from failed
events (error kind + failing tool_result bodies) into a durable error_snippets
list — paths/numbers/uuids/addrs stripped so the same error collapses to one
fingerprint with a count; Python traceback header skipped in favour of the real
exception line. Durable in Tier 2 (survives Tier 1 eviction). SCHEMA_VERSION ->
2 (re-ingest needed to populate). 7 new tests; suite 95/95 green.

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

tests/test_digest_errors.py

@@ -0,0 +1,74 @@
+"""Error-body mining into the digest (WP-0006 T01)."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from session_memory.core.digest import (  # noqa: E402
+    _error_fingerprint,
+    _error_snippets,
+    build_digest,
+)
+from session_memory.core.schema import SCHEMA_VERSION, Session, SessionEvent  # noqa: E402
+
+
+def _ev(seq, kind, **kw):
+    return SessionEvent(session_uid="claude:s", seq=seq, kind=kind, **kw)
+
+
+def test_fingerprint_normalizes_paths_numbers_ids():
+    a = _error_fingerprint("ModuleNotFoundError: No module named 'foo' at /home/x/a.py:42")
+    b = _error_fingerprint("ModuleNotFoundError: No module named 'foo' at /srv/y/b.py:9991")
+    assert a == b  # paths + line numbers stripped -> same fingerprint
+    assert "<path>" in a and "<n>" in a
+
+
+def test_fingerprint_uuid_and_addr():
+    fp = _error_fingerprint("connection 0xDEADBEEF to 1972d1d9-fc35-4912-8126-1fe64cc51425 failed")
+    assert "<addr>" in fp and "<uuid>" in fp
+
+
+def test_snippets_dedup_and_count():
+    blobs = {"b1": "Traceback...\nValueError: bad thing at /p/x.py:10",
+             "b2": "Traceback...\nValueError: bad thing at /q/y.py:99",
+             "b3": "KeyError: 'id'"}
+    events = [
+        _ev(0, "error", payload_ref="b1"),
+        _ev(1, "error", payload_ref="b2"),       # same fingerprint as b1
+        _ev(2, "error", payload_ref="b3"),
+    ]
+    snips = _error_snippets(events, blobs)
+    assert len(snips) == 2
+    top = snips[0]
+    assert top["count"] == 2  # the ValueError collapsed
+    assert "ValueError" in top["sample"]
+
+
+def test_failed_tool_result_mined():
+    blobs = {"b1": "npm ERR! something failed with non-zero exit"}
+    events = [_ev(0, "tool_result", tool="Bash", payload_ref="b1")]
+    snips = _error_snippets(events, blobs)
+    assert len(snips) == 1
+    assert snips[0]["tool"] == "Bash"
+
+
+def test_clean_tool_result_not_mined():
+    blobs = {"b1": "6 passed in 0.4s"}
+    events = [_ev(0, "tool_result", tool="Bash", payload_ref="b1")]
+    assert _error_snippets(events, blobs) == []
+
+
+def test_build_digest_includes_error_snippets_and_v2():
+    s = Session(session_uid="claude:s", flavor="claude", native_session_id="s", repo="r")
+    events = [_ev(0, "user_msg"), _ev(1, "error", payload_ref="b1"), _ev(2, "assistant_msg")]
+    d = build_digest(s, events, {"b1": "RuntimeError: kaboom at /a/b.py:3"})
+    assert d["schema_version"] == SCHEMA_VERSION == 2
+    assert d["error_snippets"][0]["count"] == 1
+    assert "RuntimeError" in d["error_snippets"][0]["sample"]
+
+
+def test_no_errors_empty_list():
+    s = Session(session_uid="claude:s", flavor="claude", native_session_id="s", repo="r")
+    d = build_digest(s, [_ev(0, "user_msg"), _ev(1, "assistant_msg")])
+    assert d["error_snippets"] == []