docs: correct stated defaults in Chroma pipeline docstrings

[iridescentWen]

Fixes #14668

Third docs PR after #14345 and #14541 (both merged).

What's wrong

The three Chroma pipelines' __call__ docstrings state defaults to X for seven parameters where
the signature uses a different value. Anyone who reads the docstring and passes the documented number
explicitly gets different behavior than omitting the argument — which is the opposite of what a
stated default is for.

Every value below was read from the corresponding __call__ signature via AST, not inferred:

File	__call__	Parameter	Docstring said	Signature
pipeline_chroma.py	:589	num_inference_steps	50	35
pipeline_chroma.py	:589	guidance_scale	3.5	5.0
pipeline_chroma_img2img.py	:648	guidance_scale	3.5	5.0
pipeline_chroma_inpainting.py	:766	num_inference_steps	35	28
pipeline_chroma_inpainting.py	:766	guidance_scale	3.5	7.0
pipeline_chroma_inpainting.py	:766	strength	0.9	0.6
pipeline_chroma_inpainting.py	:766	max_sequence_length	512	256

The pattern looks like the docstrings were carried between the three pipelines (and from a Flux-style
ancestor) while the signatures were retuned per pipeline. Note the internal evidence that
defaults to really is meant to mirror the literal signature default here: in the same
pipeline_chroma.py docstring, num_images_per_prompt (defaults to 1) and
max_sequence_length (defaults to 512) both match their signature exactly — only these seven drifted.

Docstrings only, no behavior change.

Correct ones left alone

Not everything the scan surfaced was wrong, and I did not touch what already agrees:
pipeline_chroma_img2img.py's num_inference_steps (35) and strength (0.9) both match, as does
max_sequence_length (512) in pipeline_chroma.py and pipeline_chroma_img2img.py.

How I found it, and one thing I got wrong on the way

An AST pass comparing each documented defaults to <literal> against the signature's actual literal
default. It reports only when both sides are comparable literals, and deliberately skips two classes
that are not defects: a None signature default whose docstring names the value resolved in the
body (intentional), and prose defaults like "defaults to the model's current device".

Worth flagging because it nearly produced a wrong entry above: my first pass used a file-wide grep for
max_sequence_length: and picked up encode_prompt's signature (= 512) instead of __call__'s
(= 256), which would have made the inpainting row look correct. The table is built from
per-function AST lookups for that reason.

Validation

$ uvx ruff check src/diffusers/pipelines/chroma/
All checks passed!

$ uvx ruff format --check src/diffusers/pipelines/chroma/
5 files already formatted

Re-running the scan over src/diffusers/pipelines/chroma after the change reports 0 mismatches.

git diff --stat: 3 files, +7/-7.

Self-review (per CONTRIBUTING)

Ran the .ai/skills/self-review rubric against .ai/review-rules.md:

• Blocking issues: none. Docstring text only; no logic, signatures, or defaults changed.
• # Copied from: all three __call__ methods checked individually — none carries a
  # Copied from header (the markers in these files sit on helpers like encode_prompt and
  _pack_latents), so editing the three docstrings directly is correct rather than fixing an upstream
  source and running make fix-copies. utils/check_copies.py is outside my sparse checkout, so this
  is the manual equivalent; CI's consistency check will confirm.
• Ephemeral context: none added.
• Documentation impact: this is the documentation fix; no docs/ page repeats these numbers
  (checked docs/source/en/api/pipelines/chroma.md).
• Dead code analysis: not applicable.

Not claimed

The same scan finds ~190 more defaults to mismatches elsewhere in src/diffusers/, heavily
clustered in other pipeline families (num_inference_steps 50 → 28 in 13 files,
guidance_scale 7.5 → 5.0 in 12, and so on). I kept this PR to one pipeline family rather than
sending a repo-wide sweep. If you'd like the rest, tell me whether you prefer them per-family or as
one batch and I'll follow up — and if you'd rather this were enforced mechanically instead, that scan
could become a utils/ check.

---

🤖 Written with Claude Code. All seven signature defaults were read
programmatically and the correct-already entries were verified rather than assumed.

[github-actions]

Hi @iridescentWen, thanks for the PR! It does not appear to link an issue it fixes. If this PR addresses an existing issue, please add a closing keyword (e.g. Fixes #1234) to the PR description so the issue is linked. See the contribution guide for more details. If this PR intentionally does not fix a tracked issue, a maintainer can add the no-issue-needed label to silence this reminder.

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[stevhliu]

thanks for the fixes!

[HuggingFaceDocBuilderDev]

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