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>

src/lembas/services/prompts.py

@@ -1025,21 +1025,38 @@ BUILTIN: tuple[Fragment, ...] = (
         group=GROUP_TOOLS,
         order=243,
         families=("image",),
-        hint="Appears when image generation is offered. The sentence about the "
-        "picture already being on screen is the one that earns its place: "
-        "without it the commonest thing a model does next is offer to show you "
-        "the image, which it has no way of doing and which has already "
-        "happened.",
+        hint="Appears when image generation is offered. Two sentences here earn "
+        "their place against the tool's own descriptions. The picture already "
+        "being on screen, because without it the commonest thing a model does "
+        "next is offer to show you the image — which it cannot do and which has "
+        "already happened. And the shape of a prompt: a small model left to "
+        "itself passes the request through verbatim, which is why so many "
+        "generations look like nobody thought about them.",
         default=(
-            "- You can draw a picture with image_generate. Describe what you want in "
-            "the prompt as fully as you can — subject, setting, lighting, style — "
-            "because the prompt is the whole of what the picture is made from.\n"
-            "- The picture appears in the conversation as soon as the tool returns. "
-            "It is already on screen: do not offer to show it, link to it or "
-            "describe how to open it.\n"
-            "- Only the prompt is required. Everything else has a sensible default, "
-            "so set a parameter when you have a reason to and leave it out "
-            "otherwise. Repeat a seed to get the same picture again."
+            "- You can draw a picture with image_generate. Only `prompt` is required.\n"
+            "- Write the prompt as a description, not as the request you were given. "
+            "Comma-separated phrases work better than a sentence, and the order matters "
+            "— subject first, then what it is doing, then the setting, then the light, "
+            "then the style and medium. \"a red bicycle\" is a worse prompt than \"a red "
+            "bicycle leaning on a whitewashed wall, morning light, long shadows, 35mm "
+            "photograph, shallow depth of field\". Expand what you were asked for into "
+            "one of these; do not ask the person to write it for you.\n"
+            "- Use `negative` for what must not appear, as plain nouns: \"blurry, extra "
+            "fingers, text, watermark\". Never phrase it as an instruction — \"no text\" "
+            "puts text in the picture.\n"
+            "- Set `width` and `height` to suit the subject rather than leaving both at "
+            "the default: taller than wide for a person, wider than tall for a place. "
+            "Match the size the checkpoint expects; far above it produces duplicated "
+            "limbs rather than more detail.\n"
+            "- The other parameters have sensible defaults. Change one when you have a "
+            "reason — fewer steps for a quick draft, lower cfg when a picture looks "
+            "harsh — and leave it out otherwise.\n"
+            "- The picture appears in the conversation as soon as the tool returns. It "
+            "is already on screen: do not offer to show it, link to it, or describe how "
+            "to open it. Say what you made and what you would change.\n"
+            "- If it fails because the machine ran out of video memory, try once more at "
+            "a smaller size or with a lighter checkpoint. Do not repeat the same request "
+            "unchanged."
         ),
     ),
     Fragment(