Working chat: auth, connections, streaming, folders

LLeMbas now runs end to end. Register, add an OpenAI-compatible
connection, and hold a real streaming conversation organised into
folders. Verified against the local llama-swap instance.

Streaming is the one genuinely tricky part. Sending a message returns
two HTML fragments -- the user bubble and an empty assistant bubble
carrying an sse-connect -- and that attribute is the ONLY thing that
starts a generation. Rendering an incomplete assistant message as a
streaming shell falls out of the same template, which means loading a
page whose last reply never finished simply picks it up again.

Details worth knowing about, each commented where it matters:

- SSE payloads are split across several data: lines. A raw newline in
  one data: line truncates the event, which shows up the first time a
  model emits a code block.
- Markdown is rendered server-side by the same helper for both the page
  and the final streamed frame, so the two cannot disagree. The fence
  renderer is replaced outright rather than using markdown-it's
  highlight option, which re-wraps output in a second <pre>.
- escape_text is html.escape, not nh3.clean_text: it escapes character
  by character, so escaping stream chunks separately equals escaping
  the whole string.
- The stream opens its own session via session_scope(); it outlives the
  request handler and the dependency-scoped session may be closed.
- Deleting a folder keeps the chats inside it (FK is SET NULL). Losing
  a conversation to a mis-clicked folder delete is unforgivable.
- Login failures use one message for "no such account" and "wrong
  password" so the form cannot enumerate registered addresses.

Also adds deploy/ for the gamebox install at https://chat.lan: system
unit, nginx vhost with buffering off (buffering on turns streaming into
one lump at the end), and install/update scripts following the same
service-user and /srv bind-mount conventions as llama-swap and comfyui.

70 tests, ruff clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lembas/api/folders.py

@@ -0,0 +1,118 @@
+"""Folder management."""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, Form, HTTPException, Response, status
+from sqlalchemy.orm import Session as DBSession
+
+from lembas.api.deps import Db, RequiredUser
+from lembas.db.models import Folder
+
+router = APIRouter(prefix="/api/folders", tags=["folders"])
+
+MAX_DEPTH = 8
+
+
+def _owned_folder(db: DBSession, folder_id: str, user_id: str) -> Folder:
+    folder = db.get(Folder, folder_id)
+    if folder is None or folder.user_id != user_id:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "That folder no longer exists.")
+    return folder
+
+
+def _depth_of(db: DBSession, folder: Folder | None) -> int:
+    depth = 0
+    seen: set[str] = set()
+    while folder is not None and folder.id not in seen:
+        seen.add(folder.id)
+        depth += 1
+        folder = db.get(Folder, folder.parent_id) if folder.parent_id else None
+    return depth
+
+
+def _refresh_sidebar() -> Response:
+    """Tell the browser to reload so the tree re-renders.
+
+    The folder tree is recursive and a change can move any part of it, so
+    re-rendering the whole sidebar server-side is both simpler and less
+    error-prone than trying to patch individual nodes over the wire.
+    """
+    response = Response(status_code=status.HTTP_204_NO_CONTENT)
+    response.headers["HX-Refresh"] = "true"
+    return response
+
+
+@router.post("")
+async def create_folder(
+    db: Db,
+    user: RequiredUser,
+    name: str = Form("New folder"),
+    parent_id: str = Form(""),
+) -> Response:
+    parent = _owned_folder(db, parent_id, user.id) if parent_id else None
+
+    # A cap on nesting, so a runaway client cannot build a tree deep enough to
+    # blow the recursion limit in the template.
+    if parent is not None and _depth_of(db, parent) >= MAX_DEPTH:
+        raise HTTPException(
+            status.HTTP_400_BAD_REQUEST,
+            f"Folders cannot be nested more than {MAX_DEPTH} deep.",
+        )
+
+    db.add(
+        Folder(
+            user_id=user.id,
+            name=name.strip()[:200] or "New folder",
+            parent_id=parent.id if parent else None,
+        )
+    )
+    db.commit()
+    return _refresh_sidebar()
+
+
+@router.patch("/{folder_id}")
+async def update_folder(
+    db: Db,
+    user: RequiredUser,
+    folder_id: str,
+    name: str | None = Form(None),
+    parent_id: str | None = Form(None),
+    collapsed: bool | None = Form(None),
+) -> Response:
+    folder = _owned_folder(db, folder_id, user.id)
+
+    if name is not None and name.strip():
+        folder.name = name.strip()[:200]
+
+    if parent_id is not None:
+        new_parent = _owned_folder(db, parent_id, user.id) if parent_id else None
+        # Reparenting a folder into its own subtree would detach that subtree
+        # from the root and make it unreachable.
+        cursor = new_parent
+        while cursor is not None:
+            if cursor.id == folder.id:
+                raise HTTPException(
+                    status.HTTP_400_BAD_REQUEST,
+                    "A folder cannot be moved inside itself.",
+                )
+            cursor = db.get(Folder, cursor.parent_id) if cursor.parent_id else None
+        folder.parent_id = new_parent.id if new_parent else None
+
+    if collapsed is not None:
+        folder.collapsed = collapsed
+
+    db.commit()
+    return _refresh_sidebar()
+
+
+@router.delete("/{folder_id}")
+async def delete_folder(db: Db, user: RequiredUser, folder_id: str) -> Response:
+    """Delete a folder. Child folders go with it; chats do not.
+
+    Chats fall back to the unfiled list (the FK is ON DELETE SET NULL), because
+    losing a conversation to a mis-clicked folder delete is unforgivable.
+    """
+    folder = _owned_folder(db, folder_id, user.id)
+    db.delete(folder)
+    db.commit()
+    return _refresh_sidebar()