Files
LLeMbas/src/lembas/services/images/tool.py
T
Jaroslav Beneš 60e7d0d599 Say what actually failed, and tell the model how to use the thing
Two problems, both found by looking rather than by guessing.

ComfyUI writes its history entry in task_done and nowhere else, so the entry
appearing IS "finished" -- but it sets completed=e.success, which means an
out-of-memory, a cancelled job and a broken node all stay completed:false for
ever. await_images waited on that flag. So every failure sat for the full 600s
timeout and then reported a timeout, when ComfyUI had known within one second and
written down the node, the exception type and the message. Proved by causing both
against the real instance: an OOM now raises in 1.0s and an interrupt in 4.0s,
each naming the node.

The terminal condition is a record with a status, and status.messages is read for
the last execution_error or execution_interrupted. OutOfMemory and Interrupted
are their own classes because they are the two failures with an obvious next
move: the first tells the model to retry at a named smaller size -- worked out
from what it actually asked for, since "use a lower resolution" against a request
that was already 512x512 is advice nobody can follow -- or with a lighter
checkpoint; the second says somebody pressed stop, so do not simply start again.
Everything else gets the reason and no advice, because a model told to try again
after a broken workflow tries the identical thing.

The OOM message is cut to its first sentence. The rest is allocator advice --
PYTORCH_CUDA_ALLOC_CONF, fragmentation notes -- addressed to whoever runs the box
and meaningless to a model, in a tool result that is already a failure.

Second: the parameters were described in the register of a reference table, and
"cfg: prompt adherence, default 8" tells a model nothing it can act on. Measured
on a 4B model, same request, same everything else: with the old wording it sent
prompt and template and nothing more -- so 512x512 on an SDXL checkpoint, which
is exactly the duplicated-limbs failure the width description now warns about.
With descriptions that say what each value does to the picture and when to move
it, the same model sent a portrait 1024x1536 and a deliberate sampler. ~3KB of
schema per request in a chat that can draw, and the difference between having ten
parameters and having one.

docs/image-generation-instructions.md is the long version for the admin
instructions box, for models that need more than the harness can afford to carry
on every request in every chat.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-05 14:55:18 +02:00

633 lines
26 KiB
Python

"""The tool that makes a picture, and the loop that decides to keep it.
One call is one finished image. The alternative -- return every attempt to the
conversation and let the model decide whether to call again -- costs a full
round per retry, makes the ceiling advisory rather than enforced, and shows the
reader every reject on the way past. So the retrying happens here, and what
comes back is the image that was kept.
**Three things are ordered rather than incidental.**
*The reviewer is asked about bytes, not about a row.* An attempt that is going
to be thrown away should not leave an `Attachment` behind, so the judge is shown
a downscaled preview built in memory and only the kept image is ever written.
*Preserve VRAM swaps around the review, not around the tool.* The sequence is
unload the LLM, generate, free ComfyUI, ask the reviewer (which loads the LLM
again), and round once more if it said no. Two model loads per retry, which is
why the two settings are independent and the admin page says so.
*Nothing loads the LLM back at the end.* The reply's next request does it, and
llama-swap -- or Ollama, or anything else worth pointing this at -- loads on
demand. A step that exists in the description and not in the code looks like an
omission, so it is said here instead.
"""
from __future__ import annotations
import json
import logging
from dataclasses import dataclass
from typing import Any
import httpx
from sqlalchemy import select
from lembas.services.images import comfy, workflow
from lembas.services.llm.openai_client import Endpoint, LLMError, complete
from lembas.services.tools import RISK_WRITE, ToolContext, ToolDef, ToolOutcome
log = logging.getLogger(__name__)
# What the reviewer is allowed to write back. It is one verdict and one line of
# reason, and a model that writes an essay about a picture is a model whose
# answer nobody reads.
MAX_VERDICT_TOKENS = 200
# How long to wait for a connection to admit it has unloaded. Short: this is a
# hint before a slow operation, and a machine that will not answer it is one
# where the generation should go ahead anyway rather than fail.
UNLOAD_TIMEOUT = 30.0
SCHEMA: dict[str, Any] = {
"type": "object",
"properties": {
# First, and the only required one, because `tools.parse_arguments`
# puts the whole raw string into the first required parameter when a
# model emits arguments that are not valid JSON. That failure is common
# with small models, and this way it degrades into a prompt rather than
# into a seed.
"prompt": {
"type": "string",
"description": "What to draw. Describe the subject, the setting and the style.",
},
# Every description below says what the value *does to the picture* and
# when to move it, not what it is called. A model that is told "cfg:
# prompt adherence, default 8" has been told nothing it can act on, and
# the observable result is a model that sends the prompt alone and
# leaves ten parameters at their defaults for ever.
"negative": {
"type": "string",
"description": (
"Comma-separated things to keep OUT of the picture, as plain nouns and "
"adjectives: 'blurry, extra fingers, text, watermark'. Not a sentence, "
"and never phrased as an instruction — 'do not add text' puts *text* in "
"the picture. Defaults to 'text, watermark'."
),
},
"template": {
"type": "string",
"description": "Which workflow to use. Omit to use this chat's usual one.",
},
"model": {
"type": "string",
"description": (
"Which checkpoint to draw with. Pick by what it is good at; omit to use "
"this chat's usual one."
),
},
"seed": {
"type": "integer",
"description": (
"Omit it, or pass -1, for a new random image. Repeat a seed you were "
"told about to get that same image again — which is how you change one "
"thing about a picture and keep the rest."
),
},
"steps": {
"type": "integer",
"description": (
"How long to refine, 1-150. Default 20. Around 20-30 for most things; "
"8-12 for a quick draft or when several are wanted; 40+ only for fine "
"detail, and past about 50 it stops improving and only costs time."
),
},
"cfg": {
"type": "number",
"description": (
"How literally to follow the prompt, 0-30. Default 8. 3-6 gives the "
"model room and looks more natural; 7-9 is the usual range; 12+ forces "
"the words through and starts to look burnt and over-saturated. Lower "
"it if the picture looks harsh, raise it if the subject is being "
"ignored."
),
},
"width": {
"type": "integer",
"description": (
"Pixels, 64-2048, a multiple of 8. Default 512. Use the size the "
"checkpoint was trained for — about 512 for SD1.5, about 1024 for SDXL "
"— and change the ratio rather than the total: 512x768 for a portrait, "
"768x512 for a landscape. Going far above what the checkpoint expects "
"produces duplicated limbs and repeated horizons, not more detail."
),
},
"height": {
"type": "integer",
"description": (
"Pixels, 64-2048, a multiple of 8. Default 512. See width: the aspect "
"ratio is the thing to choose, and taller than wide suits a person, "
"wider than tall suits a place."
),
},
"sampler": {
"type": "string",
"description": (
"How the image is solved. Default euler. 'euler' is safe and fast; "
"'dpmpp_2m' is a good general improvement; 'dpmpp_2m_sde' for more "
"texture; 'ddim' for a clean flat look. Leave it out unless you have a "
"reason."
),
},
"scheduler": {
"type": "string",
"description": (
"How the steps are spaced. Default normal. 'karras' pairs well with the "
"dpmpp samplers and usually helps at low step counts; 'normal' "
"otherwise. Leave it out unless you are also setting the sampler."
),
},
"denoise": {
"type": "number",
"description": (
"How much of the starting noise to replace, 0-1. Default 1, which is "
"what you want for a picture drawn from nothing. Lower values only mean "
"something for a workflow that starts from an existing image."
),
},
},
"required": ["prompt"],
}
@dataclass(frozen=True)
class Attempt:
"""One generated image and what was decided about it."""
number: int
seed: int
kept: bool
verdict: str = ""
def config_of(context: ToolContext) -> comfy.Config:
"""The client snapshot, with the key decrypted at the last moment."""
from lembas.services.crypto import decrypt
values = context.image_config or {}
return comfy.Config(
base_url=str(values.get("base_url") or ""),
api_key=decrypt(str(values.get("api_key_encrypted") or "")),
timeout=float(values.get("timeout") or comfy.DEFAULT_TIMEOUT),
)
def _choices(db, values: dict[str, Any]) -> tuple[list[Any], list[str]]:
"""The templates and checkpoints on offer, for the schema and the harness."""
from lembas.db.models import ImageWorkflow
rows = list(
db.scalars(
select(ImageWorkflow)
.where(ImageWorkflow.enabled.is_(True))
.order_by(ImageWorkflow.position, ImageWorkflow.slug)
)
)
return rows, [str(name) for name in (values.get("checkpoints") or [])]
def schema_for(db, values: dict[str, Any]) -> dict[str, Any]:
"""The parameter schema, with this instance's own choices in it.
`template` and `model` become enums because a name that does not exist is a
refusal from ComfyUI and a wasted round; `sampler` and `scheduler` stay
plain strings because there are forty-four and nine of them, and an enum
that size costs tokens on every request forever to prevent a mistake worth
one sentence of correction.
"""
rows, checkpoints = _choices(db, values)
schema = json.loads(json.dumps(SCHEMA))
if rows:
schema["properties"]["template"]["enum"] = [row.slug for row in rows]
schema["properties"]["template"]["description"] = "Which workflow to use. " + "; ".join(
f"{row.slug}: {row.description or row.name}" for row in rows[:12]
)
if checkpoints:
schema["properties"]["model"]["enum"] = checkpoints
return schema
def tool_def(db, values: dict[str, Any]) -> ToolDef:
return ToolDef(
name="image_generate",
family="image",
description=(
"Draw a picture from a description and show it to the person you are "
"talking to. Returns once the image has been made and is on screen."
),
parameters=schema_for(db, values),
run=run,
# Not RISK_READ: it spends somebody's GPU for a minute and puts a new
# artefact in the conversation. In an agent chat that means the mode
# decides whether to ask first, which is the right answer for a call
# that cannot be undone by reading something again.
risk=RISK_WRITE,
)
# --- Preserve VRAM -------------------------------------------------------------
async def _unload_llm(context: ToolContext) -> bool:
"""Ask this chat's own endpoint to drop its model. Best-effort.
*This chat's own* is the whole of the design. The unload hook is a column on
`Connection`, so a chat talking to a local llama-swap unloads that and a
chat talking to a box on the network unloads nothing -- its VRAM is not the
VRAM ComfyUI is about to want.
"""
from lembas.db.models import Connection
from lembas.db.session import session_scope
url = ""
method = "POST"
try:
with session_scope() as db:
connection = db.get(Connection, context.connection_id)
if connection is not None:
url = (connection.unload_url or "").strip()
method = (connection.unload_method or "POST").upper()
except Exception: # noqa: BLE001 - a hint that could not be looked up is not a failure
log.debug("could not read the unload hook", exc_info=True)
return False
if not url:
return False
try:
async with httpx.AsyncClient(timeout=UNLOAD_TIMEOUT) as client:
await client.request(method, url)
return True
except Exception: # noqa: BLE001 - see the module docstring: a hint, not a step
log.info("could not unload the model at %s", url, exc_info=True)
return False
# --- The reviewer --------------------------------------------------------------
def _reviewer(context: ToolContext) -> tuple[Endpoint, str] | None:
"""The model that judges an image, or None if there is nobody to ask.
The admin's choice first, then the chat's own model when it has vision. A
chat on a text-only model with no reviewer configured simply keeps the first
image, which is the behaviour with review switched off -- said here rather
than failing, because "you asked for a picture and got an error about
vision" is a worse answer than a picture.
"""
from lembas.db.models import Connection, Model
from lembas.db.session import session_scope
values = context.image_config or {}
if not values.get("review_enabled"):
return None
wanted = str(values.get("review_model_id") or "")
try:
with session_scope() as db:
model = None
if wanted:
model = db.get(Model, wanted)
if model is None and context.model_id:
model = db.scalar(
select(Model).where(
Model.model_id == context.model_id,
Model.connection_id == context.connection_id,
)
)
if model is None or not (model.capabilities_json or {}).get("vision"):
return None
connection = db.get(Connection, model.connection_id)
if connection is None or not connection.enabled:
return None
return Endpoint.from_connection(connection), model.model_id
except Exception: # noqa: BLE001 - no reviewer is a degraded mode, not an error
log.warning("could not resolve an image reviewer", exc_info=True)
return None
async def _review(
context: ToolContext, endpoint: Endpoint, model_id: str, prompt: str, payload: bytes
) -> tuple[bool, str]:
"""Show the reviewer the image and ask whether to keep it.
Answers `(keep, reason)`. **Anything that goes wrong is a keep**: the
reviewer is a second opinion on a picture that already exists, and losing an
image because a judging request timed out would be the check destroying the
thing it was checking.
"""
from lembas.db.session import session_scope
from lembas.services import files as files_service
from lembas.services import prompts as prompts_service
preview = files_service.preview_data_uri(payload, max_edge=768)
if preview is None:
return True, ""
with session_scope() as db:
instruction = prompts_service.resolve(db, "task.image_review")
# An administrator who cleared the fragment has switched reviewing off, the
# same way clearing `task.compact` switches compaction off. Nothing is asked
# of anyone and the image is kept.
if not instruction.strip():
return True, ""
body = {
"model": model_id,
"messages": [
{"role": "system", "content": instruction},
{
"role": "user",
"content": [
{"type": "text", "text": f"The request was: {prompt}"},
{"type": "image_url", "image_url": {"url": preview}},
],
},
],
"max_tokens": MAX_VERDICT_TOKENS,
"temperature": 0,
}
try:
answer = (await complete(endpoint, body)).strip()
except LLMError as exc:
log.info("could not review a generated image: %s", exc.message)
return True, ""
verdict, _, reason = answer.partition("\n")
keep = not verdict.strip().upper().startswith("RETRY")
return keep, (reason or verdict).strip()[:300]
# --- The runner ----------------------------------------------------------------
async def run(context: ToolContext, args: dict[str, Any]) -> ToolOutcome:
"""Generate one image, review it if there is anybody to ask, and keep one."""
from lembas.db.session import session_scope
from lembas.services import files as files_service
event: dict[str, Any] = {
"name": "image_generate",
"kind": "image",
"query": str(args.get("prompt") or "")[:200],
"results": [],
}
prompt = str(args.get("prompt") or "").strip()
if not prompt:
return ToolOutcome(
"No prompt was given, so nothing was drawn. Say what the picture should show.",
{**event, "status": "error", "error": "No prompt."},
)
if not context.chat_id:
return ToolOutcome(
"Images can only be generated inside a chat.",
{**event, "status": "error", "error": "No chat."},
)
values = context.image_config or {}
config = config_of(context)
if not config.configured:
return ToolOutcome(
"No image generator is configured on this instance.",
{**event, "status": "error", "error": "No ComfyUI configured."},
)
# Resolve the template and the checkpoint: what the model asked for, then
# this chat's usual, then the instance default. Every rung is a preference
# and none of them is a constraint, which is what lets a model that only
# wrote a prompt still get a picture.
try:
with session_scope() as db:
rows, checkpoints = _choices(db, values)
wanted = str(args.get("template") or "")
chosen = _pick(rows, wanted, context.image_workflow_id, values)
if chosen is None:
return ToolOutcome(
"No image workflow has been set up on this instance.",
{**event, "status": "error", "error": "No workflow."},
)
template = json.loads(json.dumps(chosen.workflow_json or {}))
template_slug, template_name = chosen.slug, chosen.name
except ToolOutcome: # pragma: no cover - defensive
raise
except Exception as exc: # noqa: BLE001
log.exception("could not resolve an image workflow")
return ToolOutcome(
f"The image workflow could not be read: {exc}",
{**event, "status": "error", "error": str(exc)},
)
checkpoint = _checkpoint(str(args.get("model") or ""), context.image_checkpoint, checkpoints)
if checkpoint is None:
return ToolOutcome(
"No checkpoint is available. An administrator has to list them on the "
"image generation page.",
{**event, "status": "error", "error": "No checkpoint."},
)
given = {name: args.get(name) for name in workflow.PLACEHOLDERS if name in args}
given["model"] = checkpoint
given["prompt"] = prompt
reviewer = _reviewer(context)
tries = int(values.get("max_tries") or 1) if reviewer else 1
preserve = bool(values.get("preserve_vram"))
attempts: list[Attempt] = []
kept: tuple[bytes, dict[str, Any]] | None = None
# What the last attempt actually asked for, so a failure can name concrete
# numbers back at the model rather than saying "try something smaller".
params_used: dict[str, Any] = workflow.resolve(given)
try:
for number in range(1, tries + 1):
if preserve:
await _unload_llm(context)
params = workflow.resolve({**given, "seed": args.get("seed") if number == 1 else None})
params_used = params
refs = await comfy.await_images(
config, await comfy.submit(config, workflow.fill(template, params))
)
if not refs:
raise comfy.ComfyError("ComfyUI finished but saved no image.")
payload = await comfy.fetch_image(config, refs[0])
if preserve:
await comfy.free(config)
if reviewer is None:
attempts.append(Attempt(number, params["seed"], kept=True))
kept = (payload, params)
break
endpoint, model_id = reviewer
keep, reason = await _review(context, endpoint, model_id, prompt, payload)
last = number == tries
attempts.append(Attempt(number, params["seed"], kept=keep or last, verdict=reason))
if keep or last:
kept = (payload, params)
break
except comfy.ComfyError as exc:
if preserve:
# It failed *inside* the far side, so its models are still resident
# and the language model is still unloaded. Freeing here is what
# lets the reply carry on and say what happened.
await comfy.free(config)
return ToolOutcome(
f"The image could not be generated: {exc.message}{_advice(exc, params_used)}",
{**event, "status": "error", "error": exc.message},
)
if preserve:
await comfy.free(config)
if kept is None: # pragma: no cover - the loop always keeps its last attempt
return ToolOutcome(
"Nothing was generated.", {**event, "status": "error", "error": "No image."}
)
payload, params = kept
try:
with session_scope() as db:
attachment = files_service.store(
db,
user_id=context.owner_id,
chat_id=context.chat_id,
payload=payload,
filename=f"{template_slug}-{params['seed']}.png",
# What ComfyUI made, at the size it made it. See `_keep_image`.
keep_original=True,
source_label="Image generation",
source_path=f"{checkpoint} · seed {params['seed']}",
)
attachment_id = attachment.id
width, height = attachment.width, attachment.height
except Exception as exc: # noqa: BLE001
log.exception("could not store a generated image")
return ToolOutcome(
f"The image was generated but could not be saved: {exc}",
{**event, "status": "error", "error": str(exc)},
)
return ToolOutcome(
_describe(prompt, template_name, checkpoint, params, attempts),
{
**event,
"status": "ok",
"detail": f"{template_name} · {checkpoint}",
"text": _transcript(params, attempts),
# Bound to the reply by `generation._persist`, the single writer. A
# runner may create the row; only the loop may say which turn owns
# it.
"attachment_id": attachment_id,
"image": {"id": attachment_id, "width": width, "height": height},
},
)
def _advice(exc: comfy.ComfyError, params: dict[str, Any]) -> str:
"""What to do about a failure, when there is something to do about it.
Only for the two that have an obvious next move. Everything else gets the
reason and nothing else -- a model told to "try again" after a broken
workflow will try the identical thing, and a suggestion invented for a
failure nobody understands is a guess wearing the application's authority.
The numbers are concrete on purpose. "Use a lower resolution" against a
request that was already 512x512 is advice that cannot be followed, so the
halved size is worked out here where the request is known.
"""
if isinstance(exc, comfy.Interrupted):
return (
" Somebody stopped it deliberately, so do not simply start it again — say so and ask."
)
if not isinstance(exc, comfy.OutOfMemory):
return ""
width, height = int(params.get("width") or 512), int(params.get("height") or 512)
smaller = f"{max(256, width // 2)}x{max(256, height // 2)}"
return (
f" Try once more at a smaller size — {smaller} instead of {width}x{height} — "
"or with a lighter checkpoint if one is offered. Do not repeat the same "
"request unchanged; it will run out of memory again."
)
def _pick(rows: list[Any], wanted: str, chat_default: str, values: dict[str, Any]) -> Any:
"""The workflow to use: asked for, then the chat's, then the instance's."""
by_slug = {row.slug: row for row in rows}
if wanted and wanted in by_slug:
return by_slug[wanted]
by_id = {row.id: row for row in rows}
if chat_default and chat_default in by_id:
return by_id[chat_default]
fallback = str(values.get("default_workflow_id") or "")
if fallback and fallback in by_id:
return by_id[fallback]
return rows[0] if rows else None
def _checkpoint(wanted: str, chat_default: str, available: list[str]) -> str | None:
"""The checkpoint to draw with, on the same ladder.
A name the instance does not have is ignored rather than passed through: it
would reach ComfyUI, be refused, and cost a round to discover -- and the
model was shown the list it may choose from.
"""
if wanted and wanted in available:
return wanted
if chat_default and chat_default in available:
return chat_default
return available[0] if available else None
def _describe(
prompt: str, template: str, checkpoint: str, params: dict[str, Any], attempts: list[Attempt]
) -> str:
"""What the model reads back.
It is told the image is already on screen, because otherwise the commonest
next thing it does is offer to show it -- and there is nothing it could do
to comply.
"""
lines = [
"The image has been generated and is shown to them. It is not a link and "
"needs no further action.",
f"Prompt: {prompt}",
f"Template {template}, checkpoint {checkpoint}, "
f"{params['width']}x{params['height']}, seed {params['seed']}, "
f"{params['steps']} steps, cfg {params['cfg']}.",
]
if len(attempts) > 1:
rejected = [a for a in attempts if not a.kept]
lines.append(
f"It took {len(attempts)} attempts; the earlier ones were rejected on review "
f"({'; '.join(a.verdict for a in rejected if a.verdict) or 'no reason given'})."
)
return "\n".join(lines)
def _transcript(params: dict[str, Any], attempts: list[Attempt]) -> str:
"""What the reader sees when they open the tool block.
The rejected attempts are recorded here and their images are not kept. A
transcript full of pictures somebody's model decided against is noise, and
the disk they would occupy buys nothing -- what is worth knowing is that it
took three goes and why the first two did not do.
"""
lines = [
f"seed {params['seed']} · {params['steps']} steps · cfg {params['cfg']} · "
f"{params['sampler']}/{params['scheduler']} · denoise {params['denoise']}"
]
if len(attempts) > 1:
lines.append("")
for attempt in attempts:
state = "kept" if attempt.kept else "rejected"
reason = f" — {attempt.verdict}" if attempt.verdict else ""
lines.append(f"Attempt {attempt.number} (seed {attempt.seed}): {state}{reason}")
return "\n".join(lines)