card: add the test_06 fixture sample, with a caveat about synthetic sources

README.md

@@ -92,6 +92,27 @@ output was stable across the whole range — so with a descriptive prompt these
 settings are forgiving. Below ~0.3 you get little more than a gloss pass; above
 ~0.85 the source becomes a loose suggestion.
 
+
+### The repo's own test fixture
+
+`tests/sdxl/test_06_source.png` with the test plan's `DEFAULT_PROMPT`, through both checkpoints.
+
+<table>
+<tr><td><img src="https://huggingface.co/ChrisColeTech/sdxl/resolve/main/samples/fixture-source.png" width="250" alt="test_06 fixture source"></td><td><img src="https://huggingface.co/ChrisColeTech/sdxl/resolve/main/samples/fixture-juggernaut.png" width="250" alt="Juggernaut on the fixture source"></td><td><img src="https://huggingface.co/ChrisColeTech/sdxl/resolve/main/samples/fixture-illustrious.png" width="250" alt="Illustrious on the fixture source"></td></tr>
+<tr><td><sub>**source** — `tests/sdxl/test_06_source.png`, a synthetic gradient</sub></td><td><sub>**img2img prompt:** `a colorful vibrant landscape painting, mountains lake sunset clouds, thick oil paint brushstrokes, high detail, 4k ultra detailed` — **Juggernaut XL v9**, 1024×1024, **25 steps**, **guidance 7.5**, **strength 0.75**, seed 42</sub></td><td><sub>**img2img prompt:** `a colorful vibrant landscape painting, mountains lake sunset clouds, thick oil paint brushstrokes, high detail, 4k ultra detailed` — **Illustrious Anime v4**, 1024×1024, **25 steps**, **guidance 7.5**, **strength 0.75**, seed 42</sub></td></tr>
+</table>
+
+**A caveat about this fixture, not the model.** The source is a synthetic gradient
+with a flat circle. The result gains real vertical brushwork and holds luminance
+(1.00× and 1.03× of source), but the prompt's *content* — mountains, lake, sunset —
+never appears, because at `strength 0.75` the source's geometry dominates and there
+is no semantic content to reinterpret.
+
+That also makes this fixture unable to detect the failure that matters: with no
+subject in the source, subject loss is invisible. It is why `strength 0.90` passes
+here and discards the subject on a photograph. **Validate img2img against a real
+photograph as well.**
+
 ## Recommended settings
 
 Values this build is run with in practice. They are read out of a live config when this card is generated, so they cannot drift from what is actually used.