feat: drawer branching UI (T98.1)

chat/templates/_drawer.html

@@ -414,6 +414,48 @@
     {% endif %}
   </section>
 
+  <section class="drawer-section">
+    <h3>Branches</h3>
+    {% if branches %}
+      <ul class="branch-list">
+        {% for b in branches %}
+          <li class="branch-row{% if b.is_active %} branch-active{% endif %}">
+            <strong>{{ b.name }}</strong>
+            {% if b.is_active %}<span class="muted"> (active)</span>{% endif %}
+            <span class="muted"> &middot; {{ b.event_count }} events</span>
+            {% if not b.is_active %}
+              <form class="inline-edit"
+                    hx-post="/chats/{{ chat.id }}/drawer/branch/switch"
+                    hx-target="#drawer" hx-swap="innerHTML">
+                <input type="hidden" name="name" value="{{ b.name }}">
+                <button type="submit">Switch</button>
+              </form>
+            {% endif %}
+          </li>
+        {% endfor %}
+      </ul>
+    {% else %}
+      <p class="muted">No branches yet.</p>
+    {% endif %}
+    <details>
+      <summary>Create branch</summary>
+      <form class="inline-edit"
+            hx-post="/chats/{{ chat.id }}/drawer/branch/create"
+            hx-target="#drawer" hx-swap="innerHTML">
+        <label>
+          Name:
+          <input type="text" name="name" required
+                 placeholder="e.g. experiment_a">
+        </label>
+        <label>
+          Origin event id:
+          <input type="number" name="origin_event_id" required min="0">
+        </label>
+        <button type="submit">Create</button>
+      </form>
+    </details>
+  </section>
+
   <section class="drawer-section">
     <h3>Pinned memories ({{ pinned|length }} / {{ pin_cap }})</h3>
     {% if pinned %}

chat/web/drawer.py

@@ -36,7 +36,14 @@ from fastapi.responses import HTMLResponse
 from fastapi.templating import Jinja2Templates
 
 from chat.eventlog.log import append_and_apply
+from chat.services.branching import (
+    branch_from_event,
+    list_branches_with_metadata,
+    switch_active_branch,
+)
+from chat.services.delete_impact import compute_delete_impact
 from chat.services.relationship_seed import seed_inter_bot_edges
+from chat.services.rewind import execute_rewind
 from chat.services.scene_summarize import apply_scene_close_summary
 from chat.state.edges import get_edge
 from chat.state.entities import get_bot, get_you, list_bots
@@ -169,6 +176,11 @@ async def drawer(chat_id: str, request: Request, conn=Depends(get_conn)):
     active_events = list_active_events(conn, chat_id)
     open_threads = list_open_threads(conn, chat_id)
 
+    # T98.1: branch metadata (every chat sees the global branch list — branches
+    # may be chat-scoped or global, so :func:`list_branches_with_metadata`
+    # returns both flavours and the template highlights the active one).
+    branches = list_branches_with_metadata(conn, chat_id)
+
     return TEMPLATES.TemplateResponse(
         request,
         "_drawer.html",
@@ -196,6 +208,7 @@ async def drawer(chat_id: str, request: Request, conn=Depends(get_conn)):
             "pin_cap": PIN_CAP,
             "active_events": active_events,
             "open_threads": open_threads,
+            "branches": branches,
         },
     )
 
@@ -1080,3 +1093,98 @@ async def close_thread(
         },
     )
     return await drawer(chat_id, request, conn)
+
+
+# --- T98.1 branching UI --------------------------------------------------
+#
+# Three POST endpoints wired to the Phase 4 :mod:`chat.services.branching`
+# helpers. The drawer's "Branches" panel exposes:
+#
+# * Create from a free-form ``origin_event_id``.
+# * Switch the active branch by name.
+# * Convenience "branch from this turn" against a per-turn event_id (the
+#   chat surface stamps ``id="turn-<event_id>"`` on every turn so users can
+#   pick the right one without copying ids by hand).
+#
+# All three return the refreshed drawer partial; failures from the service
+# layer (duplicate name, unknown branch, invalid origin) surface as 400 so
+# HTMX displays the inline error.
+
+
+@router.post(
+    "/chats/{chat_id}/drawer/branch/create",
+    response_class=HTMLResponse,
+)
+async def create_branch(
+    chat_id: str,
+    request: Request,
+    name: str = Form(...),
+    origin_event_id: int = Form(...),
+    conn=Depends(get_conn),
+):
+    chat = get_chat(conn, chat_id)
+    if chat is None:
+        raise HTTPException(status_code=404, detail=f"chat not found: {chat_id}")
+    try:
+        branch_from_event(
+            conn,
+            name=name,
+            origin_event_id=int(origin_event_id),
+            chat_id=chat_id,
+        )
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc))
+    return await drawer(chat_id, request, conn)
+
+
+@router.post(
+    "/chats/{chat_id}/drawer/branch/switch",
+    response_class=HTMLResponse,
+)
+async def switch_branch(
+    chat_id: str,
+    request: Request,
+    name: str = Form(...),
+    conn=Depends(get_conn),
+):
+    chat = get_chat(conn, chat_id)
+    if chat is None:
+        raise HTTPException(status_code=404, detail=f"chat not found: {chat_id}")
+    try:
+        switch_active_branch(conn, name=name)
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc))
+    return await drawer(chat_id, request, conn)
+
+
+@router.post(
+    "/chats/{chat_id}/drawer/branch/from-turn/{event_id}",
+    response_class=HTMLResponse,
+)
+async def branch_from_turn(
+    chat_id: str,
+    event_id: int,
+    request: Request,
+    name: str = Form(...),
+    conn=Depends(get_conn),
+):
+    """Convenience: branch from a specific turn event.
+
+    Identical to :func:`create_branch` except ``origin_event_id`` is
+    encoded in the URL — the chat surface renders one such form per turn
+    so users can fork mid-conversation without authoring an event id by
+    hand.
+    """
+    chat = get_chat(conn, chat_id)
+    if chat is None:
+        raise HTTPException(status_code=404, detail=f"chat not found: {chat_id}")
+    try:
+        branch_from_event(
+            conn,
+            name=name,
+            origin_event_id=int(event_id),
+            chat_id=chat_id,
+        )
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc))
+    return await drawer(chat_id, request, conn)

tests/test_drawer_phase4.py

@@ -0,0 +1,189 @@
+"""T98 (Phase 4): drawer phase-4 bundle.
+
+Five sub-features extending the chat drawer:
+
+* T98.1 — branching UI (create / switch / from-turn).
+* T98.2 — significance-review panel (distribution + significance edits).
+* T98.3 — hide-from-view toggle (per-turn, via ``manual_edit`` projector
+  branch ``turn_hidden``).
+* T98.4 — surgical delete with cascade preview (preview modal +
+  rewind execution against a target turn).
+* T98.5 — remaining v1 edits (chat narrative_anchor + weather).
+
+Tests follow the T59 pattern in ``tests/test_drawer_events_threads_skip.py``
+— a TestClient against the real FastAPI app with a per-test temp DB.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from fastapi.testclient import TestClient
+
+from chat.app import app
+from chat.db.connection import open_db
+from chat.eventlog.log import append_and_apply, append_event
+from chat.eventlog.projector import project
+
+
+@pytest.fixture
+def client(tmp_path, monkeypatch):
+    cfg = tmp_path / "config.toml"
+    cfg.write_text('featherless_api_key = "test"\n')
+    monkeypatch.setenv("CHAT_CONFIG_PATH", str(cfg))
+    db = tmp_path / "test.db"
+    monkeypatch.setenv("CHAT_DB_PATH", str(db))
+    with TestClient(app) as c:
+        if hasattr(app.state, "background_worker"):
+            app.state.background_worker.enabled = False
+        yield c
+
+
+def _bot_payload(bot_id: str, name: str) -> dict:
+    return {
+        "id": bot_id,
+        "name": name,
+        "persona": "...",
+        "voice_samples": [],
+        "traits": [],
+        "backstory": "",
+        "initial_relationship_to_you": "",
+        "kickoff_prose": "",
+    }
+
+
+def _seed_chat(db: Path, *, with_scene: bool = True) -> int:
+    """Seed a chat hosted by ``bot_a``; return the latest event id (chat_created)."""
+    with open_db(db) as conn:
+        append_event(conn, kind="bot_authored", payload=_bot_payload("bot_a", "BotA"))
+        append_event(
+            conn,
+            kind="you_authored",
+            payload={"name": "Me", "pronouns": "they/them", "persona": ""},
+        )
+        chat_event_id = append_event(
+            conn,
+            kind="chat_created",
+            payload={
+                "id": "chat_bot_a",
+                "host_bot_id": "bot_a",
+                "initial_time": "2026-04-26T20:00:00+00:00",
+                "narrative_anchor": "Day 1",
+                "weather": "",
+            },
+        )
+        if with_scene:
+            append_event(
+                conn,
+                kind="scene_opened",
+                payload={
+                    "chat_id": "chat_bot_a",
+                    "container_id": None,
+                    "started_at": "2026-04-26T20:00:00+00:00",
+                    "participants": ["you", "bot_a"],
+                },
+            )
+        project(conn)
+        return chat_event_id
+
+
+# ---------------------------------------------------------------------------
+# T98.1 — branching UI.
+# ---------------------------------------------------------------------------
+
+
+def test_t98_1_create_branch_emits_branch_created_and_renders(client, tmp_path):
+    db = tmp_path / "test.db"
+    seed_id = _seed_chat(db)
+
+    response = client.post(
+        "/chats/chat_bot_a/drawer/branch/create",
+        data={"name": "experiment_a", "origin_event_id": str(seed_id)},
+    )
+    assert response.status_code == 200
+
+    with open_db(db) as conn:
+        rows = conn.execute(
+            "SELECT COUNT(*) FROM event_log WHERE kind = 'branch_created'"
+        ).fetchone()
+        assert rows[0] == 1
+        from chat.state.branches import get_branch
+
+        b = get_branch(conn, "experiment_a")
+        assert b is not None
+        assert b["origin_event_id"] == seed_id
+        assert b["chat_id"] == "chat_bot_a"
+
+    # Drawer partial lists the new branch.
+    body = response.text
+    assert "<h3>Branches</h3>" in body
+    assert "experiment_a" in body
+
+
+def test_t98_1_switch_branch_marks_active_and_unknown_400s(client, tmp_path):
+    db = tmp_path / "test.db"
+    seed_id = _seed_chat(db)
+
+    # Create branch directly via the service so this test focuses on switch.
+    with open_db(db) as conn:
+        from chat.services.branching import branch_from_event
+
+        branch_from_event(
+            conn, name="experiment_b", origin_event_id=seed_id, chat_id="chat_bot_a"
+        )
+
+    response = client.post(
+        "/chats/chat_bot_a/drawer/branch/switch",
+        data={"name": "experiment_b"},
+    )
+    assert response.status_code == 200
+
+    with open_db(db) as conn:
+        from chat.state.branches import active_branch
+
+        active = active_branch(conn)
+        assert active is not None
+        assert active["name"] == "experiment_b"
+
+    # Unknown branch -> 400.
+    bad = client.post(
+        "/chats/chat_bot_a/drawer/branch/switch",
+        data={"name": "ghost_branch"},
+    )
+    assert bad.status_code == 400
+
+
+def test_t98_1_branch_from_turn_emits_branch_created(client, tmp_path):
+    db = tmp_path / "test.db"
+    seed_id = _seed_chat(db)
+
+    # Append an extra turn so we can branch from it specifically.
+    with open_db(db) as conn:
+        turn_id = append_event(
+            conn,
+            kind="user_turn",
+            payload={"chat_id": "chat_bot_a", "prose": "hi", "segments": []},
+        )
+
+    response = client.post(
+        f"/chats/chat_bot_a/drawer/branch/from-turn/{turn_id}",
+        data={"name": "fork_at_turn"},
+    )
+    assert response.status_code == 200
+
+    with open_db(db) as conn:
+        from chat.state.branches import get_branch
+
+        b = get_branch(conn, "fork_at_turn")
+        assert b is not None
+        assert b["origin_event_id"] == turn_id
+        assert b["chat_id"] == "chat_bot_a"
+
+    # Duplicate name -> 400 from service ValueError.
+    dup = client.post(
+        f"/chats/chat_bot_a/drawer/branch/from-turn/{turn_id}",
+        data={"name": "fork_at_turn"},
+    )
+    assert dup.status_code == 400
+    assert seed_id < turn_id  # sanity: turn is after chat_created