Add the assistant: a chat that drives the MCP tools in-process

A provider set under Settings (OpenAI-compatible; key encrypted in
flow-data/ai.json) turns on an Assistant panel in the sidebar. Each turn runs
the FastMCP tools in-process as the person chatting, streams the rounds over
SSE and keeps one transcript per user. The panel floats on any screen and
shares the editor's lane: a settings panel keeps the top half, the chat the
bottom. The MCP client is now built once, for the endpoint and the chat.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/code/agents.md

@@ -95,6 +95,25 @@ door could write one the canvas cannot open.
 The caller's token rides along on every hop, so the API sees the agent's own
 identity rather than a service account. The audit trail on Home names it.
 
+## The assistant
+
+The same tools drive the chat inside the dashboard. An operator sets a
+provider under **Settings → Assistant** (anything OpenAI-compatible: OpenAI,
+Anthropic, OpenRouter, a local Ollama), and an **Assistant** entry appears in
+the sidebar for everyone. The panel opens on any screen and keeps its place
+from screen to screen; on a flow, it knows which one you are looking at.
+
+The model calls the tools above, in-process, as **you**: every call carries
+your own token, so the chat can do nothing you could not do yourself, and its
+edits show up in the editor as drafts the moment they are saved. It is told to
+publish only when asked, but it has the tool, so read what it did before
+saying so. The trace under each answer lists every call it made.
+
+The conversation is one per person, kept on the instance beside the
+configuration, and the bin in the panel's header starts it over. `MCP_ENABLED`
+is not needed for it: the endpoint is for agents outside, the chat for the
+one inside.
+
 ## A note on working this way
 
 The pattern that works is the same one that works with a person: let the agent