diff --git a/chat/db/migrations/0010_threads.sql b/chat/db/migrations/0010_threads.sql
new file mode 100644
index 0000000..6f61d33
--- /dev/null
+++ b/chat/db/migrations/0010_threads.sql
@@ -0,0 +1,14 @@
+CREATE TABLE threads (
+    id INTEGER PRIMARY KEY,
+    thread_id TEXT NOT NULL UNIQUE,
+    chat_id TEXT NOT NULL,
+    title TEXT NOT NULL,
+    summary TEXT NOT NULL DEFAULT '',
+    status TEXT NOT NULL DEFAULT 'open',
+    opened_at TEXT NOT NULL DEFAULT (datetime('now')),
+    closed_at TEXT,
+    last_referenced_scene_id INTEGER,
+    created_at TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at TEXT NOT NULL DEFAULT (datetime('now'))
+);
+CREATE INDEX threads_chat_status_idx ON threads(chat_id, status);
diff --git a/chat/state/threads.py b/chat/state/threads.py
new file mode 100644
index 0000000..6aa6407
--- /dev/null
+++ b/chat/state/threads.py
@@ -0,0 +1,123 @@
+from __future__ import annotations
+from sqlite3 import Connection
+
+from chat.eventlog.projector import on
+from chat.eventlog.log import Event
+
+
+@on("thread_opened")
+def _apply_thread_opened(conn: Connection, e: Event) -> None:
+    p = e.payload
+    conn.execute(
+        "INSERT OR IGNORE INTO threads "
+        "(thread_id, chat_id, title, summary, status) "
+        "VALUES (?, ?, ?, ?, 'open')",
+        (
+            p["thread_id"],
+            p["chat_id"],
+            p["title"],
+            p.get("summary", ""),
+        ),
+    )
+
+
+@on("thread_updated")
+def _apply_thread_updated(conn: Connection, e: Event) -> None:
+    p = e.payload
+    # Idempotent: closed threads ignore subsequent updates.
+    conn.execute(
+        "UPDATE threads SET summary = ?, last_referenced_scene_id = ?, "
+        "updated_at = datetime('now') "
+        "WHERE thread_id = ? AND status = 'open'",
+        (
+            p.get("summary", ""),
+            p.get("last_referenced_scene_id"),
+            p["thread_id"],
+        ),
+    )
+
+
+@on("thread_closed")
+def _apply_thread_closed(conn: Connection, e: Event) -> None:
+    p = e.payload
+    conn.execute(
+        "UPDATE threads SET status = 'closed', closed_at = ?, "
+        "updated_at = datetime('now') "
+        "WHERE thread_id = ? AND status = 'open'",
+        (p.get("closed_at"), p["thread_id"]),
+    )
+
+
+def get_thread(conn: Connection, thread_id: str) -> dict | None:
+    row = conn.execute(
+        "SELECT thread_id, chat_id, title, summary, status, "
+        "opened_at, closed_at, last_referenced_scene_id, "
+        "created_at, updated_at "
+        "FROM threads WHERE thread_id = ?",
+        (thread_id,),
+    ).fetchone()
+    if not row:
+        return None
+    return {
+        "thread_id": row[0],
+        "chat_id": row[1],
+        "title": row[2],
+        "summary": row[3],
+        "status": row[4],
+        "opened_at": row[5],
+        "closed_at": row[6],
+        "last_referenced_scene_id": row[7],
+        "created_at": row[8],
+        "updated_at": row[9],
+    }
+
+
+def list_open_threads(conn: Connection, chat_id: str) -> list[dict]:
+    rows = conn.execute(
+        "SELECT thread_id, chat_id, title, summary, status, "
+        "opened_at, closed_at, last_referenced_scene_id, "
+        "created_at, updated_at "
+        "FROM threads WHERE chat_id = ? AND status = 'open' "
+        "ORDER BY id ASC",
+        (chat_id,),
+    ).fetchall()
+    return [
+        {
+            "thread_id": r[0], "chat_id": r[1], "title": r[2],
+            "summary": r[3], "status": r[4],
+            "opened_at": r[5], "closed_at": r[6],
+            "last_referenced_scene_id": r[7],
+            "created_at": r[8], "updated_at": r[9],
+        }
+        for r in rows
+    ]
+
+
+def list_threads(conn: Connection, chat_id: str, status: str | None = None) -> list[dict]:
+    if status is None:
+        rows = conn.execute(
+            "SELECT thread_id, chat_id, title, summary, status, "
+            "opened_at, closed_at, last_referenced_scene_id, "
+            "created_at, updated_at "
+            "FROM threads WHERE chat_id = ? ORDER BY id ASC",
+            (chat_id,),
+        ).fetchall()
+    else:
+        rows = conn.execute(
+            "SELECT thread_id, chat_id, title, summary, status, "
+            "opened_at, closed_at, last_referenced_scene_id, "
+            "created_at, updated_at "
+            "FROM threads WHERE chat_id = ? AND status = ? "
+            "ORDER BY id ASC",
+            (chat_id, status),
+        ).fetchall()
+    return [
+        {
+            "thread_id": r[0], "chat_id": r[1], "title": r[2],
+            "summary": r[3], "status": r[4],
+            "opened_at": r[5], "closed_at": r[6],
+            "last_referenced_scene_id": r[7],
+            "created_at": r[8], "updated_at": r[9],
+        }
+        for r in rows
+    ]
diff --git a/tests/test_threads_state.py b/tests/test_threads_state.py
new file mode 100644
index 0000000..6d6482d
--- /dev/null
+++ b/tests/test_threads_state.py
@@ -0,0 +1,181 @@
+from __future__ import annotations
+
+from chat.db.connection import open_db
+from chat.db.migrate import apply_migrations
+from chat.eventlog.log import append_and_apply, append_event
+from chat.eventlog.projector import project
+import chat.state.entities  # registers handlers
+import chat.state.world  # registers handlers
+import chat.state.threads  # registers handlers
+from chat.state.threads import get_thread, list_open_threads
+
+
+def _bot_payload(bot_id: str, name: str) -> dict:
+    return {
+        "id": bot_id,
+        "name": name,
+        "persona": "thoughtful, observant",
+        "voice_samples": [],
+        "traits": [],
+        "backstory": "",
+        "initial_relationship_to_you": "coworker",
+        "kickoff_prose": "",
+    }
+
+
+def _chat_payload(chat_id: str = "chat_bot_a") -> dict:
+    return {
+        "id": chat_id,
+        "host_bot_id": "bot_a",
+        "guest_bot_id": "bot_b",
+        "initial_time": "2026-04-26T20:00:00+00:00",
+        "narrative_anchor": "Day 1 evening",
+        "weather": "clear",
+    }
+
+
+def test_thread_opened_creates_row(tmp_path):
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    with open_db(db) as conn:
+        append_event(conn, kind="bot_authored", payload=_bot_payload("bot_a", "BotA"))
+        append_event(conn, kind="chat_created", payload=_chat_payload())
+        append_event(
+            conn,
+            kind="thread_opened",
+            payload={
+                "thread_id": "thr_abc",
+                "chat_id": "chat_bot_a",
+                "title": "Maya's job hunt",
+                "summary": "Maya is looking for a new job",
+            },
+        )
+        project(conn)
+
+        t = get_thread(conn, "thr_abc")
+        assert t is not None
+        assert t["thread_id"] == "thr_abc"
+        assert t["chat_id"] == "chat_bot_a"
+        assert t["title"] == "Maya's job hunt"
+        assert t["summary"] == "Maya is looking for a new job"
+        assert t["status"] == "open"
+        assert t["closed_at"] is None
+        assert t["last_referenced_scene_id"] is None
+
+
+def test_thread_updated_changes_summary_and_last_referenced(tmp_path):
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    with open_db(db) as conn:
+        append_event(conn, kind="bot_authored", payload=_bot_payload("bot_a", "BotA"))
+        append_event(conn, kind="chat_created", payload=_chat_payload())
+        append_event(
+            conn,
+            kind="thread_opened",
+            payload={
+                "thread_id": "thr_abc",
+                "chat_id": "chat_bot_a",
+                "title": "Maya's job hunt",
+                "summary": "Maya is looking for a new job",
+            },
+        )
+        append_event(
+            conn,
+            kind="thread_updated",
+            payload={
+                "thread_id": "thr_abc",
+                "summary": "Maya landed an interview at a startup",
+                "last_referenced_scene_id": 42,
+            },
+        )
+        project(conn)
+
+        t = get_thread(conn, "thr_abc")
+        assert t is not None
+        assert t["summary"] == "Maya landed an interview at a startup"
+        assert t["last_referenced_scene_id"] == 42
+        assert t["status"] == "open"
+
+
+def test_thread_closed_terminal(tmp_path):
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    with open_db(db) as conn:
+        append_event(conn, kind="bot_authored", payload=_bot_payload("bot_a", "BotA"))
+        append_event(conn, kind="chat_created", payload=_chat_payload())
+        append_event(
+            conn,
+            kind="thread_opened",
+            payload={
+                "thread_id": "thr_abc",
+                "chat_id": "chat_bot_a",
+                "title": "Maya's job hunt",
+                "summary": "Maya is looking for a new job",
+            },
+        )
+        append_event(
+            conn,
+            kind="thread_closed",
+            payload={
+                "thread_id": "thr_abc",
+                "closed_at": "2026-04-26T21:00:00+00:00",
+            },
+        )
+        project(conn)
+
+        t = get_thread(conn, "thr_abc")
+        assert t is not None
+        assert t["status"] == "closed"
+        assert t["closed_at"] == "2026-04-26T21:00:00+00:00"
+
+        # Subsequent updates to a closed thread are no-ops.
+        append_and_apply(
+            conn,
+            kind="thread_updated",
+            payload={
+                "thread_id": "thr_abc",
+                "summary": "should not be applied",
+            },
+        )
+
+        t2 = get_thread(conn, "thr_abc")
+        assert t2 is not None
+        assert t2["summary"] == "Maya is looking for a new job"
+        assert t2["status"] == "closed"
+
+
+def test_list_open_threads_filters_to_open_only(tmp_path):
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    with open_db(db) as conn:
+        append_event(conn, kind="bot_authored", payload=_bot_payload("bot_a", "BotA"))
+        append_event(conn, kind="chat_created", payload=_chat_payload())
+        for tid, title in [
+            ("thr_1", "Arc 1"),
+            ("thr_2", "Arc 2"),
+            ("thr_3", "Arc 3"),
+        ]:
+            append_event(
+                conn,
+                kind="thread_opened",
+                payload={
+                    "thread_id": tid,
+                    "chat_id": "chat_bot_a",
+                    "title": title,
+                    "summary": "",
+                },
+            )
+        append_event(
+            conn,
+            kind="thread_closed",
+            payload={
+                "thread_id": "thr_3",
+                "closed_at": "2026-04-26T21:00:00+00:00",
+            },
+        )
+        project(conn)
+
+        open_threads = list_open_threads(conn, "chat_bot_a")
+        assert len(open_threads) == 2
+        ids = {t["thread_id"] for t in open_threads}
+        assert ids == {"thr_1", "thr_2"}