feat: cross-chat search UX (top-bar + results page) (T100)

Wires T93's `search_all_memories` service into a small read-only HTML
surface so users can find a memory across every chat in the database.

* `chat/web/search.py` (new): GET `/search?q=...` runs the FTS service
  with k=50, hydrates each row with bot name + scene timestamp, and
  renders `search.html`. Empty `q` short-circuits to no results so the
  top-bar form can submit even with an empty input.
* `chat/templates/search.html` (new): empty-state placeholder, results
  list with chat-level "Open chat" links (`/chats/{chat_id}` — memories
  don't carry an event_id today, so no per-turn anchor).
* `chat/templates/layout.html`: append a small `<form>` to the rail
  nav, additive only.
* `chat/app.py`: register `search_router` (additive import + include).
* `tests/test_search_ux.py`: 3 tests — multi-chat results, empty-query
  placeholder, chat link.

chat/app.py

@@ -32,6 +32,7 @@ from chat.web.drawer import router as drawer_router
 from chat.web.kickoff import router as kickoff_router
 from chat.web.middleware import FirstRunRedirectMiddleware
 from chat.web.nav import router as nav_router
+from chat.web.search import router as search_router
 from chat.web.settings import router as settings_router
 from chat.web.sse import router as sse_router
 from chat.web.turns import router as turns_router
@@ -140,6 +141,7 @@ app.include_router(settings_router)
 app.include_router(nav_router)
 app.include_router(chat_router)
 app.include_router(drawer_router)
+app.include_router(search_router)
 app.include_router(sse_router)
 app.include_router(turns_router)
 

chat/templates/layout.html

@@ -7,6 +7,13 @@
     <li><a href="/bots" class="{% if active_nav == 'bots' %}active{% endif %}">Bots</a></li>
     <li><a href="/settings" class="{% if active_nav == 'settings' %}active{% endif %}">Settings</a></li>
   </ul>
+  {# T100: cross-chat search box. GET /search so the URL is shareable
+     and back-button friendly; the results page itself re-renders this
+     form with the query pre-filled. #}
+  <form class="rail-search" action="/search" method="get" role="search">
+    <input type="search" name="q" placeholder="Search" aria-label="Search memories">
+    <button type="submit">Go</button>
+  </form>
 </nav>
 <main class="content">
   {% block content %}{% endblock %}

chat/templates/search.html

@@ -0,0 +1,37 @@
+{% extends "layout.html" %}
+{% block title %}Search - chat{% endblock %}
+{% block content %}
+<header class="page-header">
+  <h1>Search</h1>
+</header>
+
+<form class="search-page-form" action="/search" method="get">
+  <input type="text" name="q" value="{{ query|default('', true) }}"
+         placeholder="Search memories across all chats" autofocus>
+  <button type="submit">Search</button>
+</form>
+
+{% if not query %}
+  {# Empty-state placeholder: the top-bar form submits to /search even
+     with no input, so this page must render cleanly with no query. #}
+  <p class="muted search-empty">Enter a query to search memories across all chats.</p>
+{% elif not results %}
+  <p class="muted">No matches for &ldquo;{{ query }}&rdquo;.</p>
+{% else %}
+  <ul class="search-results">
+    {% for r in results %}
+    <li class="search-result">
+      <a class="search-result-link" href="/chats/{{ r.chat_id }}">
+        <div class="search-result-meta muted">
+          <strong>{{ r.owner_name }}</strong>
+          <span>&middot; {{ r.chat_id }}</span>
+          {% if r.chat_name %}<span>&middot; {{ r.chat_name }}</span>{% endif %}
+          {% if r.scene_label %}<span>&middot; scene {{ r.scene_label }}</span>{% endif %}
+        </div>
+        <div class="search-result-summary">{{ r.pov_summary }}</div>
+      </a>
+    </li>
+    {% endfor %}
+  </ul>
+{% endif %}
+{% endblock %}

chat/web/search.py

@@ -0,0 +1,92 @@
+"""T100 (Phase 4): cross-chat search UX route.
+
+Wraps T93's :func:`chat.services.cross_chat_search.search_all_memories`
+in a small read-only HTML surface so the top-bar search input has
+somewhere to land. The route does no filtering of its own beyond the
+empty-query fast-path that T93 already implements; ranking, owner
+scope, and witness scope all live in the service layer.
+
+For each match we hydrate just enough metadata to render a row:
+* the owner bot's display name (so users see "BOTA" not "bot_a"),
+* the originating ``chat_id`` (the link target — there's no per-turn
+  anchor today because memories don't carry an ``event_id`` column,
+  so we deep-link to the chat as a whole),
+* the originating scene title when one exists,
+* and the ``pov_summary`` itself.
+
+We deliberately keep this module synchronous and template-only — no
+HTMX swaps, no JSON API — because the search box is a "leave the
+current chat to look something up" surface, not an inline drawer.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from fastapi import APIRouter, Depends, Request
+from fastapi.responses import HTMLResponse
+from fastapi.templating import Jinja2Templates
+
+from chat.services.cross_chat_search import search_all_memories
+from chat.state.entities import get_bot
+from chat.state.world import get_chat, get_scene
+from chat.web.bots import get_conn
+
+TEMPLATES = Jinja2Templates(
+    directory=str(Path(__file__).resolve().parent.parent / "templates")
+)
+
+router = APIRouter()
+
+
+@router.get("/search", response_class=HTMLResponse)
+async def search(request: Request, q: str = "", conn=Depends(get_conn)):
+    """Render ``search.html`` with up to 50 cross-chat FTS matches.
+
+    ``q`` is intentionally allowed to be empty — that path renders the
+    page's "enter a query" placeholder rather than a 400, because the
+    top-bar form submits to this URL even with an empty input. T93's
+    service short-circuits whitespace-only queries to ``[]`` so there
+    is no FTS5 ``MATCH ''`` syntax error to guard against here.
+    """
+    raw_results = search_all_memories(conn, query=q, k=50) if q else []
+
+    # Hydrate display fields per row. We do this in the route (not the
+    # service) so the service stays a pure FTS shim that other UIs
+    # can reuse.
+    results = []
+    for row in raw_results:
+        bot = get_bot(conn, row["owner_id"])
+        chat = get_chat(conn, row["chat_id"])
+        scene = get_scene(conn, row["scene_id"]) if row["scene_id"] else None
+        results.append(
+            {
+                "memory_id": row["memory_id"],
+                "owner_id": row["owner_id"],
+                "owner_name": bot["name"] if bot else row["owner_id"],
+                "chat_id": row["chat_id"],
+                "chat_name": (
+                    chat.get("narrative_anchor") if chat else None
+                ),
+                "scene_id": row["scene_id"],
+                # Scenes have no ``title`` column today; surface the
+                # ``started_at`` timestamp as a human-friendly label
+                # when a scene is set, otherwise leave it blank.
+                "scene_label": (
+                    scene.get("started_at") if scene else None
+                ),
+                "pov_summary": row["pov_summary"],
+                "significance": row["significance"],
+                "ts": row["ts"],
+            }
+        )
+
+    return TEMPLATES.TemplateResponse(
+        request,
+        "search.html",
+        {
+            "query": q,
+            "results": results,
+            "active_nav": "search",
+        },
+    )