Filter snapshot lines through --grep like change records

Snapshot indicator lines printed unconditionally under --grep, suggesting
the snapshot matched. Now the snapshot's full state is flattened into the
same (path, value) entries change records are matched against, and the
snapshot line is suppressed unless every pattern matches. Snapshots
explicitly selected with -r s<N> still print unconditionally.

tests/test_grep.py

@@ -11,6 +11,7 @@ from kanta.grep import (
     _match_value,
     evaluate,
     mark_spans,
+    matches_snapshot,
 )
 from kanta.logging import _USER_PATH
 from kanta.serialization import JsonSerializer
@@ -227,6 +228,29 @@ def test_highlighter_meta_marks_action_and_user():
     assert hl.meta("extra", "other") == "extra"
 
 
+def test_matches_snapshot_uses_change_record_matching():
+    state = {"users": {"alice": {"email": "alice@example.com", "age": 30}}}
+    assert matches_snapshot(state, _patterns("users.alice"))
+    assert matches_snapshot(state, _patterns("alice@example"))
+    assert matches_snapshot(state, _patterns("age=30"))
+    assert matches_snapshot(state, _patterns("users.alice", "=30"))
+    assert not matches_snapshot(state, _patterns("bob"))
+    assert not matches_snapshot(state, _patterns("3"))  # not a full number match
+    assert not matches_snapshot(state, _patterns("alice", "missing"))
+    assert not matches_snapshot({}, _patterns("alice"))
+
+
+def test_matches_snapshot_supports_logfmt_prettified_values():
+    state = {"when": 1767225600}
+
+    def logfmt(value, path):
+        return "2026-01-01" if value == 1767225600 else None
+
+    assert matches_snapshot(state, _patterns("2026"), logfmt=logfmt)
+    assert matches_snapshot(state, _patterns("1767225600"), logfmt=logfmt)
+    assert not matches_snapshot(state, _patterns("2026"))
+
+
 def test_entry_dataclass_holds_anchor_for_deletes():
     entry = _Entry(["a", "b"], 1, "1", anchor=["a"])
     assert entry.anchor == ["a"]
@@ -269,7 +293,7 @@ def _sample_changes():
     ]
 
 
-def _run_cli(tmp_path, capsys, monkeypatch, changes, *args, color=False):
+def _run_cli(tmp_path, capsys, monkeypatch, changes, *args, color=False, state=None):
     if color:
         monkeypatch.setenv("FORCE_COLOR", "1")
         monkeypatch.delenv("NO_COLOR", raising=False)
@@ -277,7 +301,7 @@ def _run_cli(tmp_path, capsys, monkeypatch, changes, *args, color=False):
         monkeypatch.setenv("NO_COLOR", "1")
         monkeypatch.delenv("FORCE_COLOR", raising=False)
     path = tmp_path / "test.kantadb"
-    _write_db(path, changes)
+    _write_db(path, changes, state=state)
     code = main([str(path), *args])
     assert code == 0
     return capsys.readouterr().err
@@ -335,13 +359,68 @@ def test_cli_grep_repeated_patterns_must_all_match(tmp_path, capsys, monkeypatch
 
 
 def test_cli_grep_no_match_exits_zero(tmp_path, capsys, monkeypatch):
-    """No matching records is not an error; snapshot lines still print."""
+    """No matching records is not an error; non-matching snapshots are hidden."""
     err = _run_cli(tmp_path, capsys, monkeypatch, _sample_changes(), "--grep", "nobody")
-    assert "snapshot s0" in err
+    assert "snapshot s0" not in err
     assert "create_alice" not in err
     assert "create_bob" not in err
 
 
+def test_cli_grep_snapshot_prints_only_when_state_matches(
+    tmp_path, capsys, monkeypatch
+):
+    """Snapshots are matched against their full state like change records."""
+    state = {"users": {"alice": {"email": "alice@example.com", "age": 30}}}
+
+    err = _run_cli(
+        tmp_path,
+        capsys,
+        monkeypatch,
+        _sample_changes(),
+        "--grep",
+        "alice",
+        state=state,
+    )
+    assert "snapshot s0" in err
+
+    err = _run_cli(
+        tmp_path,
+        capsys,
+        monkeypatch,
+        _sample_changes(),
+        "--grep",
+        "users.alice.age=30",
+        state=state,
+    )
+    assert "snapshot s0" in err
+
+    # A pattern matching nothing in the state suppresses the snapshot.
+    err = _run_cli(
+        tmp_path,
+        capsys,
+        monkeypatch,
+        _sample_changes(),
+        "--grep",
+        "bob",
+        state=state,
+    )
+    assert "snapshot s0" not in err
+
+    # Repeated patterns are ANDed within the snapshot state too.
+    err = _run_cli(
+        tmp_path,
+        capsys,
+        monkeypatch,
+        _sample_changes(),
+        "--grep",
+        "alice",
+        "--grep",
+        "missing",
+        state=state,
+    )
+    assert "snapshot s0" not in err
+
+
 def test_cli_grep_path_value_forms(tmp_path, capsys, monkeypatch):
     """The 'path=value', 'path=' and '=value' forms restrict the match side."""
     err = _run_cli(