refactor: unified record_turn_memory API with you_present kwarg (T84)

Extends record_turn_memory_for_present with a you_present: bool = True
kwarg so a single entry-point covers both you-scenes (witness_you=1)
and meanwhile scenes (witness_you=0). Validates that meanwhile callers
provide a guest_bot_id.

record_meanwhile_memory becomes a thin backward-compat wrapper that
delegates with you_present=False, preserving the call site in
chat/web/meanwhile.py without churn.

tests/test_memory_write.py

@@ -444,3 +444,91 @@ def test_record_for_present_dict_keys_match(tmp_path):
             narrative_text="Both bots witness this.",
         )
         assert set(result_with_guest.keys()) == {"bot_a", "bot_b"}
+
+
+# ---------------------------------------------------------------------------
+# T84: unified record_turn_memory_for_present API with you_present kwarg.
+# ---------------------------------------------------------------------------
+
+
+def test_record_turn_memory_you_present_false_writes_meanwhile_witness_mask(tmp_path):
+    """When ``you_present=False`` the witness mask should be
+    ``[you=0, host=1, guest=1]`` for both bots — the meanwhile shape."""
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    _seed_two_bots(db)
+    with open_db(db) as conn:
+        result = record_turn_memory_for_present(
+            conn,
+            chat_id="chat_ab",
+            host_bot_id="bot_a",
+            guest_bot_id="bot_b",
+            narrative_text="BotA and BotB confer privately.",
+            scene_id=None,
+            chat_clock_at="2026-04-26T20:00:00+00:00",
+            you_present=False,
+        )
+
+        assert set(result.keys()) == {"bot_a", "bot_b"}
+
+        rows = conn.execute(
+            "SELECT owner_id, witness_you, witness_host, witness_guest "
+            "FROM memories ORDER BY owner_id"
+        ).fetchall()
+        assert len(rows) == 2
+        for _owner, w_you, w_host, w_guest in rows:
+            assert w_you == 0
+            assert w_host == 1
+            assert w_guest == 1
+
+        # Two memory_written events were appended.
+        cur = conn.execute(
+            "SELECT COUNT(*) FROM event_log WHERE kind = 'memory_written'"
+        )
+        assert cur.fetchone()[0] == 2
+
+
+def test_record_turn_memory_you_present_true_default_writes_normal_witness_mask(tmp_path):
+    """Default ``you_present=True`` preserves Phase 2 behaviour:
+    ``witness_you=1`` for the host POV row."""
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    _seed_minimal(db)
+    with open_db(db) as conn:
+        # No explicit you_present arg — should default to True.
+        result = record_turn_memory_for_present(
+            conn,
+            chat_id="chat_bot_a",
+            host_bot_id="bot_a",
+            guest_bot_id=None,
+            narrative_text="BotA hums to herself.",
+        )
+        assert set(result.keys()) == {"bot_a"}
+
+        row = conn.execute(
+            "SELECT witness_you, witness_host, witness_guest "
+            "FROM memories WHERE owner_id = 'bot_a'"
+        ).fetchone()
+        assert row is not None
+        w_you, w_host, w_guest = row
+        assert w_you == 1
+        assert w_host == 1
+        assert w_guest == 0
+
+
+def test_record_turn_memory_you_present_false_requires_guest(tmp_path):
+    """Calling with ``you_present=False`` and no ``guest_bot_id`` is a
+    programming error — meanwhile scenes always have both bots."""
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    _seed_minimal(db)
+    with open_db(db) as conn:
+        with pytest.raises(ValueError, match="you_present=False requires guest_bot_id"):
+            record_turn_memory_for_present(
+                conn,
+                chat_id="chat_bot_a",
+                host_bot_id="bot_a",
+                guest_bot_id=None,
+                narrative_text="invalid",
+                you_present=False,
+            )