Draw a picture, on a ComfyUI you are running

The last unbuilt capability, and built the way CLAUDE.md said it had to be: a
ToolDef reaching resolve_tools plus a permission and a capability flag, not a new
code path. The only genuinely new UI is one branch in the transcript.

services/images/ is three modules. comfy.py speaks HTTP -- submit, poll /history,
fetch the PNG, /free, and an /object_info discovery for the admin page only.
Polled and not socketed, because holding a connection open for the length of a
generation is the live-connection state the whole ssh.py design forbids, and the
thing being waited for takes tens of seconds anyway. The base URL is exempt from
the SSRF guard by construction, exactly as Connection.base_url and the audio
endpoints are -- said out loud in the docstring, because a default of
127.0.0.1:8188 is precisely the shape that guard exists to refuse and therefore
reads as a hole rather than a decision.

workflow.py fills a template, and the one thing that matters is that it walks the
parsed JSON rather than the text of it. A value that is exactly "{{steps}}"
becomes the number 20; ComfyUI validates types and refuses the string. A
placeholder inside a longer string is still text, which is what makes
"{{prompt}}, masterpiece" work -- and text substitution would additionally mean a
prompt containing a quotation mark produced a document that no longer parses, on
the one input guaranteed to hold arbitrary text. Which node holds the prompt is
the administrator's statement rather than a guess from node types: sniffing for
the first CLIPTextEncode works on the shipped workflow and on nothing else, and
swaps positive for negative the first time somebody reorders them. seed has no
fixed default, because one would make every unspecified generation identical and
make the retry loop redraw the same rejected picture four times.

tool.py is one call, one finished image. Returning every attempt to the
conversation would cost a round each, make the ceiling advisory rather than
enforced, and walk the reader past every reject -- so the reviewer lives inside
the tool and is asked about *bytes*: an attempt about to be discarded should not
leave an Attachment behind, so it sees a downscaled preview built in memory and
only the kept image is written. Anything that goes wrong in review is a keep;
losing a picture because a judging request timed out would be the check
destroying the thing it was checking. The last attempt is kept whatever the
verdict, so a request always produces something. Rejects are recorded, not
stored.

Preserve VRAM unloads the chat's own connection and nothing else, because the
memory being freed belongs to one machine: local llama-swap answers GET /unload,
and a box on the network has no reason to be unloaded when ComfyUI wants memory
here. The swap goes round the review rather than round the tool, which costs two
model loads per retry -- so the two settings are independent and the page warns
when both are on. Nothing loads the LLM back: the reply's next request does, and
that step exists in the description and not in the code, so the code says so.

Two rules elsewhere had to be drawn for the first time. message_payload sends
images only on user turns -- no assistant message had ever carried one, and the
moment one does the multimodal list form on an assistant turn is rejected by
OpenAI and most local runners, breaking every later turn in the chat. And
files.store gained keep_original, because _process_image turns anything without
alpha into JPEG q85 at 1400px: right for a phone photo, a visible loss on the one
output this feature exists to produce.

/image sends the ordinary message with force_tool, which becomes tool_choice for
the first round only -- left in place the reply would draw a picture, be asked
again, and draw another. FORCEABLE_TOOLS is an allow list because the name is
read off a form.

ToolContext gained chat_id, and that fixed a tool nobody had ever successfully
run: _run_scratch_write read context.chat_id on a dataclass with no such field,
so every call raised AttributeError, swallowed by run_tool's blanket except into
"the scratch_write tool failed" -- indistinguishable from a model calling it
wrongly. The test that existed asserted the family and the risk, which are
properties of the declaration rather than of the code.

Verified against the real ComfyUI 0.27.0 on this machine rather than against
documentation: every endpoint shape here was read off it, a generation ran end to
end through the client, the reviewer was shown a matching and a mismatched prompt
and answered KEEP and RETRY correctly, and the unload hook fired for the local
llama-swap and not for the remote box.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/db/models/__init__.py

@@ -32,6 +32,7 @@ from lembas.db.models.chat import (
     Message,
 )
 from lembas.db.models.connection import Connection, Model, model_groups
+from lembas.db.models.image import ImageWorkflow
 from lembas.db.models.library import (
     AUTHOR_MODEL,
     AUTHOR_USER,
@@ -119,6 +120,7 @@ __all__ = [
     "Document",
     "Folder",
     "Group",
+    "ImageWorkflow",
     "KnowledgeBase",
     "McpServer",
     "Memory",

src/lembas/db/models/chat.py

@@ -218,6 +218,19 @@ class Chat(UUIDPrimaryKey, Timestamps, Base):
     # representations of "on" makes "why is this off?" unanswerable.
     scope_json: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
 
+    # What this chat generates pictures with when the model names neither. A
+    # preference rather than a constraint -- the model may still choose another
+    # template or checkpoint for a particular image, and the harness lists what
+    # is on offer -- so this is where "in this chat I am working in SDXL" is
+    # said once instead of in every prompt.
+    #
+    # Plain columns rather than keys in `scope_json`: that one narrows what a
+    # chat may *reach* and absent means on, which is the opposite of what an
+    # empty default here means. A workflow that has since been deleted reads
+    # back as no preference, so it is validated on use like `ssh_profile_id`.
+    image_workflow_id: Mapped[str | None] = mapped_column(String(32))
+    image_checkpoint: Mapped[str] = mapped_column(String(300), default="")
+
     # Which files are open in the canvas panel, and which of them is in front.
     # {"tabs": [{"key": "agent:/srv/app/main.py", "title": …, "source": …}],
     #  "active": "agent:/srv/app/main.py"}

src/lembas/db/models/connection.py

@@ -58,6 +58,18 @@ class Connection(UUIDPrimaryKey, Timestamps, Base):
     # Extra headers merged into every request (e.g. OpenRouter's HTTP-Referer).
     extra_headers_json: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
 
+    # How to ask this endpoint to drop its model from memory, for the Preserve
+    # VRAM option in image generation. Per connection and not instance-wide,
+    # because the VRAM being freed is a particular machine's: llama-swap on this
+    # host answers `GET /unload`, while a remote vLLM has no such call and no
+    # reason to be unloaded when ComfyUI needs memory *here*.
+    #
+    # Empty means "this connection cannot be unloaded", which is the honest
+    # default -- there is no call that works everywhere, and guessing one would
+    # send an unexplained request to somebody's endpoint.
+    unload_url: Mapped[str] = mapped_column(String(500), default="")
+    unload_method: Mapped[str] = mapped_column(String(8), default="POST")
+
     # Result of the most recent "Test & refresh", surfaced in the admin list.
     last_checked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     last_error: Mapped[str] = mapped_column(Text, default="")

src/lembas/db/models/image.py

@@ -0,0 +1,60 @@
+"""ComfyUI workflow templates an administrator saved.
+
+A table rather than a list inside the settings group, for the reason
+`McpServer.tools_json` is *not* a table: that one is a cache of somebody else's
+document, replaced wholesale on every refresh, where each entry carries one
+decision. These are the opposite -- authored by hand, individually named,
+edited, reordered and deleted, and referenced by id from a chat. Everything a
+table gives for free is exactly what is wanted.
+
+Deliberately **no group access list**, unlike `CustomTool`. The whole feature is
+already behind one capability flag and one permission; a second access system
+covering which templates a person may pick would be a screen of checkboxes
+nobody asked for, and the thing being restricted is the shape of a picture.
+"""
+
+from __future__ import annotations
+
+from datetime import datetime
+from typing import Any
+
+from sqlalchemy import Boolean, DateTime, Integer, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from lembas.db.base import Base, Timestamps, UUIDPrimaryKey
+from lembas.db.types import JSONDict
+
+
+class ImageWorkflow(UUIDPrimaryKey, Timestamps, Base):
+    """One API-format ComfyUI workflow, with holes where the values go."""
+
+    __tablename__ = "image_workflows"
+
+    # What the *model* names when it picks this one, so it is short and
+    # lowercase for the same reason a tool's slug is: it lands in a schema enum
+    # and is generated by something that spells inconsistently.
+    slug: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
+    name: Mapped[str] = mapped_column(String(120), nullable=False)
+
+    # Sent to the model beside the slug, and the only thing it has to choose
+    # with. "Photographic, SDXL, slow" is a choice; "workflow 2" is not.
+    description: Mapped[str] = mapped_column(Text, default="")
+
+    # The workflow itself, in ComfyUI's API format, with `{{placeholders}}`
+    # where the parameters go. Stored parsed rather than as text so the admin
+    # form can only ever save something that is valid JSON -- a template that
+    # does not parse would fail at generation time, minutes later, in front of
+    # somebody who was not editing it.
+    workflow_json: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
+
+    enabled: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    position: Mapped[int] = mapped_column(Integer, default=0, nullable=False)
+
+    # The result of the last time somebody pressed Test, in the shape
+    # `CustomTool` and `McpServer` already use, so the row reads the same way in
+    # the list as theirs do.
+    last_checked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    last_error: Mapped[str] = mapped_column(Text, default="")
+
+    def __repr__(self) -> str:
+        return f"<ImageWorkflow {self.slug}>"