[codex] add qwen3.5-4b inference example

example/inference/qwen3.5-4b/README.md

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+# Qwen3.5-4B Forward Inference Example
+
+This example is a forward-level MagiCompiler benchmark/smoke test for Qwen3.5-4B. It builds synthetic token and image tensors directly, so it does not run a tokenizer, chat template, natural-language decoder, `generate()`, or MTP path.
+
+The model implementation in `modeling.py` uses PyTorch plus `safetensors` only. It intentionally does not import `transformers`, `tokenizers`, `PIL`, or `qwen_vl_utils`.
+
+`MODEL_PATH` is optional. Omit it (or set `SKIP_LOAD_MODEL=true`) to run with the built-in Qwen3.5-4B architecture and randomly initialized weights. That path is for compile/profile work only; logits are not meaningful.
+
+## Commands
+
+Run with randomly initialized weights:
+
+```bash
+MODE=all NSYS_PROFILE=false \
+bash example/inference/qwen3.5-4b/infer.sh
+```
+
+Run the eager baseline without `magi_compile`:
+
+```bash
+COMPILE_MODE=eager MODE=all NSYS_PROFILE=false \
+bash example/inference/qwen3.5-4b/infer.sh
+```
+
+Load a local checkpoint:
+
+```bash
+MODEL_PATH=/path/to/Qwen3.5-4B MODE=all NSYS_PROFILE=false \
+bash example/inference/qwen3.5-4b/infer.sh
+```
+
+Run text prefill:
+
+```bash
+MODEL_PATH=/path/to/Qwen3.5-4B MODE=text_prefill NSYS_PROFILE=false \
+bash example/inference/qwen3.5-4b/infer.sh
+```
+
+Run text decode:
+
+```bash
+MODEL_PATH=/path/to/Qwen3.5-4B MODE=text_decode NSYS_PROFILE=false \
+bash example/inference/qwen3.5-4b/infer.sh
+```
+
+Run image prefill:
+
+```bash
+MODEL_PATH=/path/to/Qwen3.5-4B MODE=image_prefill NSYS_PROFILE=false \
+bash example/inference/qwen3.5-4b/infer.sh
+```
+
+Run image decode:
+
+```bash
+MODEL_PATH=/path/to/Qwen3.5-4B MODE=image_decode NSYS_PROFILE=false \
+bash example/inference/qwen3.5-4b/infer.sh
+```
+
+For the default `IMAGE_GRID=1,2,2`, the image modes need `SEQ_LEN>=4`.
+
+Useful environment variables:
+
+- `MODEL_PATH`: checkpoint directory, optional. When unset, the example uses the built-in Qwen3.5-4B config and random weights
+- `SKIP_LOAD_MODEL`: `true` to skip loading checkpoint weights even if `MODEL_PATH` is set, default `false`
+- `COMPILE_MODE`: `magi` to compile with MagiCompiler, or `eager` to run uncompiled PyTorch, default `magi`
+- `MODE`: `text_prefill`, `text_decode`, `image_prefill`, `image_decode`, or `all`, default `all`
+- `SEQ_LEN`: synthetic sequence length, default `128`
+- `BATCH_SIZE`: synthetic batch size, default `1`
+- `IMAGE_GRID`: one synthetic image grid as `T,H,W`, default `1,2,2`
+- `PROFILE_CNT`: timed loop count, default `3`
+- `NSYS_PROFILE`: `true` or `false`, default `true`
+- `PYTHON_BIN`: Python executable, default `python`
+- `MAGI_COMPILE_CACHE_ROOT_DIR`: MagiCompiler cache root, default repo `.cache`