[GLM-Image] Add batch > 1 support and fix configuration defaults
Author: JaredforReal
Pull request: yes

## What does this PR do?

This PR adds full batch processing support (batch_size > 1) for the GLM-Image model, fixes padding direction for autoregressive generation, and aligns configuration defaults with the official model.

Need to be used with [Diffusers GLM Image Batch Support](https://github.com/huggingface/diffusers/pull/13007)

### Problem

1. **Batch restriction**: The `GlmImageProcessor` explicitly rejected batch_size > 1
2. **Missing config defaults**: `pad_token_id` and `eos_token_id` were not set in `GlmImageTextConfig`, and `max_position_embeddings` didn't match the official config.json

### Solution

#### 1. Batch support

**Processor changes** (`processing_glm_image.py`):

- Removed the batch size restriction
- Added `images_per_sample` tensor to track number of grids per sample
- Added `num_source_images_per_sample` tensor to distinguish source images from target grids

**Model changes** (`modeling_glm_image.py` via `modular_glm_image.py`):

- Updated `get_rope_index()` to compute position IDs per-sample with batch support
- Updated `_cached_decode_position_ids` shape from `[3, max_len]` to `[batch, 3, max_len]`
- Updated `forward()` to properly handle packed `image_grid_thw` by splitting per sample
- Updated `_expand_inputs_for_generation()` and `prepare_inputs_for_generation()` for beam search compatibility

#### 2. Left padding for autoregressive generation

**Processor changes** (`processing_glm_image.py`):

- Added automatic left padding when `padding=True` is specified
- This ensures proper attention masking for autoregressive image token generation in batch mode

#### 3. Configuration alignment with official model

**Config changes** (`modular_glm_image.py` → `configuration_glm_image.py`):

- Added `pad_token_id=167841` to `GlmImageTextConfig`
- Added `eos_token_id=16385` to `GlmImageTextConfig`
- Updated `max_position_embeddings` from 32768 to 131072 to match official config.json

## Tests

All 64 modeling tests pass. Added `test_batch_consistency` to verify:

1. Batch processing produces identical predictions (argmax) as single processing
2. Identical inputs in a batch produce identical outputs

## Breaking changes

None. All new parameters are optional and backward compatible.

## Checklist

- [x] This PR fixes a bug / adds a feature without changing the model behavior
- [x] Tests pass locally
- [x] Documentation updated (docstrings for new parameters)
- [x] Code follows the project style guidelines


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Comments:
Done

cc @zucchini-nlp I think!

slow tests updated, I'm walking through the reviews, thanks

View the CircleCI Test Summary for this PR:

https://huggingface.co/spaces/transformers-community/circle-ci-viz?pr=43342&sha=464f9e

@zucchini-nlp PTAL, thanks! tested and works fine~
The CI docstring error is confusing, generated from modular file saying "run make fix-repo", ran `make fix-repo` saying diff not right.


The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_43342). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

@zucchini-nlp updated, PTAL

run-slow: glm_image

This comment contains `run-slow`, running the specified jobs: 

models: ["models/glm_image"]
quantizations: []

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/21475687201)

### Model CI Report

#### ❌ Failed tests

- [glm_image](https://github.com/huggingface/transformers/actions/runs/21475687201/job/61859528023):
    tests/models/glm_image/test_modeling_glm_image.py::GlmImageIntegrationTest::test_image_to_image_generation
    tests/models/glm_image/test_modeling_glm_image.py::GlmImageIntegrationTest::test_processor_image_to_image
    tests/models/glm_image/test_modeling_glm_image.py::GlmImageIntegrationTest::test_processor_text_to_image
    tests/models/glm_image/test_modeling_glm_image.py::GlmImageIntegrationTest::test_text_to_image_generation



@zucchini-nlp thanks!

run-slow: glm_image

This comment contains `run-slow`, running the specified jobs: 

models: ["models/glm_image"]
quantizations: []

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/21478629418)

### Model CI Report

#### ❌ Failed tests

- [glm_image](https://github.com/huggingface/transformers/actions/runs/21478629418/job/61869639007):
    tests/models/glm_image/test_modeling_glm_image.py::GlmImageIntegrationTest::test_image_to_image_generation
    tests/models/glm_image/test_modeling_glm_image.py::GlmImageIntegrationTest::test_text_to_image_generation



**[For maintainers]** Suggested jobs to run (before merge)

run-slow: glm_image


run-slow: glm_image



run-slow: glm_image

This comment contains `run-slow`, running the specified jobs: 

models: ["models/glm_image"]
quantizations: []

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/21481603313)

✅ No failing test specific to this PR 🎉 !