LLeMbas/CLAUDE.md

# CLAUDE.md

Working notes for LLeMbas. Read this before changing anything.

## What it is

A self-hosted web UI for OpenAI-compatible LLM endpoints, written in Python and
themed after Middle-earth. Server-rendered FastAPI + Jinja + htmx; SQLite;
no JavaScript build step.

## Commands

```bash
. .venv/bin/activate
pip install -e ".[dev]"

lembas serve                        # http://127.0.0.1:8080
lembas info                         # paths + counts, useful when confused
lembas secret-key                   # generate LEMBAS_SECRET_KEY
lembas create-admin                 # create or promote an admin

pytest                              # 197 tests, ~7s
ruff check .                        # lint (line length 100)
python scripts/build_artwork.py     # regenerate all SVG artwork
python scripts/fetch_vendor.py      # verify vendored JS against the lockfile
```

## Hard rules

These are the constraints the project is built around. Breaking one is a
redesign, not a tweak.

1. **No Node, no npm, no build step.** Browser libraries are downloaded once by
   `scripts/fetch_vendor.py`, hash-pinned in `scripts/vendor.lock.json`, and
   committed under `web/static/vendor/`.
2. **Nothing loads from a CDN at runtime.** A self-hosted tool must work
   offline and must not report page views to a third party.
3. **No hard-coded values outside `tokens.css`.** Every colour, space, radius
   and control height resolves through a CSS variable. `--control-h` is why
   buttons, inputs and selects line up: they all take their height from it, so
   a mixed row is flush by construction rather than by nudging.
4. **Additive-only schema changes.** SQLite only, no Alembic. `init_db()` runs
   `db/migrations.py:sync_schema()`, which creates missing tables *and* adds
   missing columns by diffing the models against the database. Renames, drops
   and retypes are still manual. See "Changing the schema" below.
5. **Secrets never reach the browser.** API keys are Fernet-encrypted at rest
   and only ever rendered masked.
6. **Model output is untrusted.** Everything from an endpoint goes through
   `services/markdown.py` (markdown-it → nh3) or `escape_text()`. Never
   `|safe` on anything that has not.

## The flavour rule

Middle-earth lives in the **artwork, theme names, empty states, loading lines
and error pages**. It does not live in the functional UI.

Chats are called *Chats*, not *Tales*. Folders are *Folders*, not *Chapters*.
Buttons say what they do. Someone who has never read the books must be able to
use this without a glossary. The two themes are named `moria` and `shire`, and
the 404 says "Not all those who wander are lost. This page, however, is." —
that is the right amount.

## Layout

```
src/lembas/
  main.py            app factory, lifespan, error handlers
  config.py          pydantic-settings, all LEMBAS_* variables
  cli.py             typer entry points
  api/
    deps.py          Db / CurrentUser / RequiredUser / AdminUser
    auth.py          register, login, logout
    pages.py         full-page routes (chat shell, settings)
    chats.py         messaging + the SSE stream
    folders.py       folder CRUD
    admin.py         connections + instance settings
    admin_models.py  model ordering, defaults, images, access
    admin_users.py   users, groups, permissions
    files.py         upload, serve, remove attachments
    preferences.py   per-user theme, default model, password
  db/
    base.py          Base, UUID/Timestamp mixins
    session.py       engine, SQLite pragmas, init_db, session_scope
    migrations.py    additive schema sync (tables + columns)
    models/          user, chat, connection, setting
  security/          passwords (argon2), sessions, permissions
  services/
    llm/openai_client.py   httpx streaming + model discovery
    chat.py          request building, endpoint resolution, titles
    markdown.py      markdown-it + pygments + nh3
    crypto.py        Fernet encrypt/decrypt/mask
    files.py         attachment validation, images, PDF/text extraction
    reasoning.py     splits thinking from the answer
    settings_store.py  runtime instance settings
    uploads.py       validated image storage
    sse.py           event framing
  web/
    templating.py    render() -- always use this, not TemplateResponse
    templates/       Jinja
    static/          css, js, vendor, img
assets/              SVG masters (generated)
deploy/              systemd unit, nginx vhost, install/update scripts
```

## Things that will bite you

**`render()`, not `TemplateResponse`.** `web/templating.py:render()` injects
`user`, `theme`, `version` and `allow_signup`. Templates assume they exist. If
you must call `templates.TemplateResponse` directly (the SSE path does, because
there is no `Request`), pass `user` explicitly — `chat/_message.html` renders
both roles and the user branch dereferences it.

**The message template is the state machine.** `chat/_message.html` renders an
incomplete assistant message as a streaming shell carrying `sse-connect`, and a
complete one as finished output. That is the *only* thing that starts a
generation. A consequence worth knowing: loading a page whose last reply is
unfinished restarts it, which is how a dropped connection recovers.

**SSE framing.** `services/sse.py:event()` splits payloads on newlines into
several `data:` lines. A raw newline in a single `data:` line truncates the
event — the failure shows up the first time a model emits a code block.

**Streaming opens its own database session.** `api/chats.py:_generate()` uses
`session_scope()`, not the request's session, because streaming outlives the
request handler.

**Escaping is chunk-safe on purpose.** `escape_text()` is `html.escape`, which
works character by character, so escaping stream chunks separately equals
escaping the whole string. `nh3.clean_text` would also be safe but escapes
spaces and slashes, tripling the size of every streamed token.

**The fence renderer is replaced, not configured.** markdown-it's `highlight`
option re-wraps output in `<pre><code>` unless the string starts with `<pre`,
which would nest a second `<pre>` inside our wrapper. `markdown.py` overrides
`renderer.rules["fence"]` instead. There is a regression test for this.

**SVG `<style>` is document-scoped.** Two text runs in one SVG sharing a class
name means the later rule recolours both. `build_artwork.py` takes class names
as parameters for exactly this reason.

**Gradient ids are document-global.** The `mark()` macro takes a `uid` because
two marks on one page with identical ids make the second silently reuse the
first one's gradients.

**Two kinds of settings.** `lembas.config` is deployment configuration read
from the environment at startup. `services/settings_store.py` is instance
settings an admin edits at runtime, stored in the `settings` table. Environment
variables seed the latter as an *initial* value only — once stored, the database
wins, or a toggle in the UI would silently revert on the next restart.

**Permissions are a union, and admins bypass them.** `security/permissions.py`
resolves a baseline (instance setting) widened by each group. A group grants;
it never denies — otherwise "why can this user not do X" needs a simulation of
every group to answer. Model *access* is separate: `models_visible_to()`.

**FastAPI cannot tell an empty form field from an absent one.** With
`x: str | None = Form(None)`, a submitted `x=` arrives as `None`, so "clear this
field" is indistinguishable from "leave it alone". `api/chats.py:update_chat`
reads `await request.form()` and checks key presence instead. Anything with a
clearable field must do the same.

**`Mapped[list]` without an element type is not a collection.** SQLAlchemy
treats a bare `Mapped[list]` as a scalar and hands back `None` instead of `[]`.
Always write `Mapped[list[Group]]`, with a `TYPE_CHECKING` import if the class
lives in another module.

**Reasoning arrives two ways.** A `reasoning_content` delta field (llama.cpp,
llama-swap, vLLM) or `<think>` tags inline in `content` (Ollama and friends).
`services/reasoning.py` handles the second with a streaming splitter, because
the tags arrive split across chunks. Reasoning is stored in `Message.reasoning`
and is deliberately **not** replayed as context on the next turn.

**Attachments are typed by their bytes, not their name.** `services/files.py`
sniffs magic numbers; a `.png` full of text is stored as text. Images are
downscaled and re-encoded (a phone photo is megabytes of base64), PDFs have
their text extracted **once at upload** — re-extracting per request would let a
reply change because a parser was upgraded.

**Images only go to models marked `vision`.** Sending content parts to an
endpoint without multimodal support is not graceful degradation; most reject
the whole request. `build_request()` checks the capability and falls back to a
plain string. A plain text turn must *stay* a plain string for the same reason.

**Attachments are served, never linked.** Images reach the model as base64 data
URIs: a local endpoint has no route back to LLeMbas and a hosted one has no
credentials. Non-images are served `Content-Disposition: attachment` with
`nosniff`, so an uploaded `.html` cannot execute in this origin.

**Uploads are unbound until the message is sent.** `Attachment.message_id` is
null in the composer; `files.claim()` binds them, and only unclaimed rows owned
by that user, so a forged id cannot pull in someone else's file. Abandoned ones
are swept at startup.

**Chats are created lazily.** There is no endpoint that makes an empty chat.
"New chat" is a link to `/chat`, which renders a composer with no row behind
it; `POST /api/chats/start` writes the chat together with its first message.
That is why an opened-and-abandoned chat never appears in the sidebar. Tests
that just need a chat use the `make_chat` fixture rather than the HTTP flow.

**Route order matters for static path segments.** FastAPI matches in
registration order, so `/admin/models/bulk` must be registered *before*
`/admin/models/{model_id}` or "bulk" is parsed as a model id and 404s. This has
already been a bug once.

**Pinning is not ordering.** The model picker is always in the administrator's
`position` order. Pinned models get shortcuts in the chat sidebar and nothing
else -- a picker whose order differs from the admin screen is just confusing.

**System prompts are precedence, not concatenation.** chat > model > instance,
most specific wins outright (`services/chat.py:effective_system_prompt`).
Stacking them reads well in a settings screen and badly in practice: two layers
that disagree give the model contradictory instructions and nobody can tell
which is losing.

**JSON columns need reassignment.** `user.settings_json["theme"] = x` on a
plain dict is not detected. The columns use `MutableDict` (`db/types.py`), but
the safe habit is `obj.field = {**obj.field, "k": v}`.

## Changing the schema

There is no Alembic, but there *is* `db/migrations.py`. It compares the declared
models against the live database and issues `ALTER TABLE ... ADD COLUMN` for
anything missing, so adding a column to a model is free: restart and it appears,
with existing rows backfilled from a type-derived default.

It cannot rename, drop or retype a column, or add a UNIQUE/PRIMARY KEY to an
existing table — SQLite mostly cannot do those with ALTER TABLE either. Those
need the create-copy-swap dance by hand; record them in `MANUAL_STEPS` so a
failure has somewhere to point.

Because the runner exists, forward-looking columns are cheap now. `Message.parent_id`
and `content_parts_json` (branching, multimodal) predate it and are still unread.

## Artwork

Do not hand-edit files in `assets/` — they are generated. Change
`scripts/build_artwork.py` and re-run it. It also copies the few files the app
serves into `web/static/img/`.

The leaf geometry is defined once (`LEAF_BLADE`, `LEAF_MIDRIB`, …) and reused by
the icon, favicon, lockup and banner. The 64×64 mark must stay legible at 16px:
the favicon variant drops the score lines, rim and veins because they turn to
mud at that size. The icon sprite is a **template partial**
(`templates/partials/icons.html`), not an asset, because same-document
`<use href="#id">` is universally supported and the cross-document form is not.

The `mark()` macro in `_macros.html` duplicates the mark geometry so it can be
inlined and themed. If the mark changes, update both.

## Deployment

`deploy/` holds a systemd unit template, an nginx vhost template, and
install/update scripts. Both templates are parameterised (`__PREFIX__`,
`__SITE_HOST__`, …) and substituted at install time, so nothing host-specific is
committed here. See `deploy/README.md`.

This repository is **public**. Keep deployment-specific hostnames, ports and
internal infrastructure detail out of it — those belong in whatever private
notes describe the machine.

## Not built yet

Built-in tools + admin tool settings, custom tools and MCP, agentic execution
(local subprocess and SSH connection profiles), image generation. Nav entries
mark where each one goes.

`Model.capabilities_json` carries a `tools` flag nothing reads yet. No OCR:
a scanned PDF is stored with an explanatory `extraction_error` rather than
silently contributing nothing.