A seed of -1 means random, as it does everywhere else

Omitting the seed was already random. Passing -1 was not: it went through the
uint64 wrap and arrived as 18446744073709551615, which is a perfectly valid
*fixed* seed -- so "give me something new" returned the identical picture every
time, silently, and the retry loop would have redrawn the same rejected image
until it ran out of attempts.

-1 is what ComfyUI's own interface uses for random, and A1111, and everything
else that has ever asked somebody for a seed. A model that has read any of them
will write it, so the one reading that had to work was the one that did not.

Any negative value, not only -1, because the sentinel is the *idea* rather than
the number and a model that writes -2 means the same thing. Zero stays a real
seed: it is the boundary this change could easily have swallowed, and it is one
somebody deliberately picks.

Confirmed against the real ComfyUI: -1 now sends a random uint64 that it accepts
and draws from.

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

tests/test_images_workflow.py

@@ -96,6 +96,27 @@ def test_a_named_seed_is_kept():
     assert wf.resolve({"prompt": "x", "seed": 1234})["seed"] == 1234
 
 
+@pytest.mark.parametrize("sentinel", [-1, -5, "-1"])
+def test_a_negative_seed_means_random(sentinel):
+    """`-1` is what ComfyUI's own interface, A1111 and everything else that has
+    ever asked for a seed use for "surprise me", so a model that has read any of
+    them will write it.
+
+    Without this it went through the uint64 wrap and came out as
+    18446744073709551615 -- a perfectly valid *fixed* seed, so asking for
+    something new produced the same picture every time.
+    """
+    seeds = {wf.resolve({"prompt": "x", "seed": sentinel})["seed"] for _ in range(8)}
+    assert len(seeds) == 8
+    assert all(0 <= seed <= wf.MAX_SEED for seed in seeds)
+
+
+def test_seed_zero_is_a_real_seed():
+    """It is the boundary the negative test could easily have swallowed, and
+    zero is a seed somebody deliberately picks."""
+    assert wf.resolve({"prompt": "x", "seed": 0})["seed"] == 0
+
+
 @pytest.mark.parametrize("empty", [None, ""])
 def test_null_and_empty_mean_no_opinion(empty):
     """A model that emits `"steps": null` rather than omitting the key is common