Users, groups, permissions, model settings and reasoning display

Four features, plus the schema machinery they needed.

**Schema sync.** The first live instance had data in it, and create_all
only creates missing *tables* -- a new column silently never appeared.
db/migrations.py now diffs the declared models against the database and
ALTER TABLE ... ADD COLUMN for what is missing, deriving a backfill
default from the column type (SQLite refuses a NOT NULL column without
one, and a Python-side `default=dict` cannot be expressed in DDL).
Verified against a copy of the live database: eight changes applied, all
rows preserved, second run a no-op. Renames, drops and retypes are still
manual and say so.

**Permissions.** A flat set of named booleans: an instance baseline
widened by each group the user belongs to. A group grants and never
denies -- with denies, "why can this user not do X" cannot be answered
without simulating every group. Admins bypass entirely, because an admin
can grant it back to themselves in two clicks and pretending otherwise
is theatre. Model *access* is separate: public, or granted to groups.
The picker is not the boundary -- switching a chat to a model you cannot
reach is a 403.

**Model settings.** Ordering, pinned-first, an instance default and a
per-user default, display names, descriptions, capability flags, and
uploaded images. Images are stored and served locally rather than by
URL: a remote URL makes every page render a request to a third party.
Uploads are validated by magic number, not the declared content type,
and stored under a random name. Models with no image get a generated
initial whose hue is derived from the model id, so it is stable.

**Reasoning display.** Streams into its own collapsible block above the
answer, labelled "Thought for 14 seconds", collapsed once finished, and
never replayed as context on the next turn. Two sources: the
reasoning_content delta field, and <think> tags inline in content -- the
latter needs a streaming splitter because the tags arrive split across
chunks. Models emitting no reasoning show nothing, via a :has() rule
rather than JavaScript. Verified against qwen35-9b on llama-swap: 694
reasoning events, 52 answer tokens, cleanly separated.

Two bugs found and fixed while testing:

- A bare `Mapped[list]` relationship is treated by SQLAlchemy as a scalar
  and returns None instead of []. It needs the element type.
- FastAPI substitutes the default for an empty form value, so with
  `x: str | None = Form(None)` a submitted `x=` is indistinguishable from
  an absent field. That silently broke clearing a system prompt or a
  temperature. update_chat now reads the raw form and checks key presence.

143 tests, ruff clean.

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

src/lembas/services/reasoning.py

@@ -0,0 +1,133 @@
+"""Separating a reasoning model's thinking from its answer.
+
+Endpoints do this two different ways and LLeMbas has to cope with both:
+
+1. A dedicated ``reasoning_content`` field in the streamed delta. This is what
+   llama.cpp, llama-swap, vLLM and DeepSeek emit, and it is unambiguous.
+2. ``<think>...</think>`` tags inline in ``content``. Ollama and various
+   proxies do this, and it is a nuisance: the tags arrive split across chunks,
+   so the text has to be scanned as a stream rather than with a regex at the
+   end.
+
+The splitter below handles the second case. It buffers only as much as a
+partial tag could occupy, so latency is unaffected in the overwhelmingly common
+case where no tag is present at all.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Iterator
+
+# Tag spellings seen in the wild. Checked longest-first so <thinking> is not
+# mistaken for <think> followed by "ing>".
+_TAGS: tuple[tuple[str, str], ...] = (
+    ("<thinking>", "</thinking>"),
+    ("<think>", "</think>"),
+    ("<reasoning>", "</reasoning>"),
+)
+
+REASONING = "reasoning"
+CONTENT = "content"
+
+# Longest opening tag, minus one: the most that can ever need holding back
+# while waiting to see whether a partial "<thi" turns into a real tag.
+_MAX_PARTIAL = max(len(open_tag) for open_tag, _ in _TAGS) - 1
+
+
+class ReasoningSplitter:
+    """Splits a stream of content chunks into reasoning and answer runs.
+
+    Feed it whatever arrives; it yields ``(kind, text)`` pairs. Call
+    :meth:`flush` at the end to release anything still buffered.
+    """
+
+    def __init__(self) -> None:
+        self._buffer = ""
+        self._in_reasoning = False
+        self._closing = ""
+
+    def feed(self, chunk: str) -> Iterator[tuple[str, str]]:
+        self._buffer += chunk
+        yield from self._drain(final=False)
+
+    def flush(self) -> Iterator[tuple[str, str]]:
+        yield from self._drain(final=True)
+
+    def _drain(self, *, final: bool) -> Iterator[tuple[str, str]]:
+        while self._buffer:
+            if self._in_reasoning:
+                index = self._buffer.find(self._closing)
+                if index == -1:
+                    # Hold back enough that a closing tag split across chunks is
+                    # still recognised once the rest arrives.
+                    keep = 0 if final else len(self._closing) - 1
+                    emit, self._buffer = self._split(keep)
+                    if emit:
+                        yield (REASONING, emit)
+                    return
+                if index:
+                    yield (REASONING, self._buffer[:index])
+                self._buffer = self._buffer[index + len(self._closing) :]
+                self._in_reasoning = False
+                self._closing = ""
+                continue
+
+            opening_at, opening, closing = self._find_opening()
+            if opening_at == -1:
+                keep = 0 if final else _MAX_PARTIAL
+                emit, self._buffer = self._split(keep)
+                if emit:
+                    yield (CONTENT, emit)
+                return
+
+            if opening_at:
+                yield (CONTENT, self._buffer[:opening_at])
+            self._buffer = self._buffer[opening_at + len(opening) :]
+            self._in_reasoning = True
+            self._closing = closing
+
+    def _find_opening(self) -> tuple[int, str, str]:
+        best = (-1, "", "")
+        for opening, closing in _TAGS:
+            index = self._buffer.find(opening)
+            if index != -1 and (best[0] == -1 or index < best[0]):
+                best = (index, opening, closing)
+        return best
+
+    def _split(self, keep: int) -> tuple[str, str]:
+        """Emit everything except the last `keep` characters."""
+        if keep <= 0:
+            return self._buffer, ""
+        if len(self._buffer) <= keep:
+            return "", self._buffer
+        return self._buffer[:-keep], self._buffer[-keep:]
+
+
+def strip_reasoning(text: str) -> tuple[str, str]:
+    """Split a complete string into (answer, reasoning).
+
+    The non-streaming counterpart, used when replaying stored content.
+    """
+    splitter = ReasoningSplitter()
+    answer: list[str] = []
+    thinking: list[str] = []
+    for kind, piece in splitter.feed(text):
+        (thinking if kind == REASONING else answer).append(piece)
+    for kind, piece in splitter.flush():
+        (thinking if kind == REASONING else answer).append(piece)
+    return "".join(answer), "".join(thinking)
+
+
+def format_duration(milliseconds: int) -> str:
+    """Human phrasing for the 'Thought for ...' label."""
+    if milliseconds <= 0:
+        return ""
+    seconds = milliseconds / 1000
+    if seconds < 1:
+        return "less than a second"
+    if seconds < 60:
+        return f"{seconds:.0f} second{'' if round(seconds) == 1 else 's'}"
+    minutes, remainder = divmod(int(seconds), 60)
+    if remainder == 0:
+        return f"{minutes} minute{'' if minutes == 1 else 's'}"
+    return f"{minutes}m {remainder}s"