add-model-07-conversion

name: add-model-07-conversion description: Use during /add-model Phase 5 to write and verify a FastVideo checkpoint conversion script after native component prototypes expose FastVideo state-dict keys/shapes.

Add Model Conversion

Goal

Convert official weights into a FastVideo-loadable component layout after Phase 4 native prototypes exist. The conversion script owns parameter mapping, component splitting, passthrough assets, config emission, and strict-load verification.

Inputs

Follow ../add-model/shared/common_rules.md for token/auth safety, state files, escape hatches, production boundaries, and skip/pass semantics.

Require the initial request from ../add-model/contracts/conversion_request.md.

If the FastVideo key/shape dump is missing, return to /add-model Phase 4. Do not write a final mapping against an unimplemented component.

For Phase 6 retry requests from component skills, also require the retry shape from ../add-model/contracts/conversion_request.md.

Output

• scripts/checkpoint_conversion/<family>_to_diffusers.py.
• converted_weights/<family>/ with model_index.json and per-component subfolders.
• Updated tests/local_tests/<model_family>/README.md with conversion command, source layout, output path, and strict-load status.
• Updated tests/local_tests/<model_family>/PORT_STATUS.md with conversion state, retry history, open questions, and issues/blockers.

Reference Scripts

• scripts/checkpoint_conversion/convert_ltx2_weights.py: component prefix splitting, metadata config extraction, passthrough Gemma/tokenizer assets, and optional component-only output.
• scripts/checkpoint_conversion/stable_audio_to_diffusers.py: monolithic model.safetensors split into transformer/VAE/conditioner, plus copied passthrough subfolders. Use this shape for single-checkpoint official repos.
• scripts/checkpoint_conversion/convert_gamecraft_full.py: separate official sources for transformer, VAE, text encoders, tokenizers, scheduler, and root model_index.json.
• scripts/checkpoint_conversion/longcat_to_fastvideo.py: fused QKV/KV split, renamed native transformer weights, and copied existing Diffusers components.
• scripts/checkpoint_conversion/pt_to_safetensors.py: simple .pt extraction helper for nested checkpoint dictionaries.

Source Layout Decision

Choose exactly one primary layout:

Monolithic checkpoints need explicit prefix ownership. For example, Stable Audio uses one model.safetensors with DiT, pretransform/VAE, and conditioner keys; the converter splits those keys into FastVideo component subfolders and writes per-component configs.

Script Shape

Start from templates/family_to_diffusers.py or the closest reference script. Keep the script explicit and reviewable:

• COMPONENT_SPECS or COMPONENT_PREFIXES declares component ownership.
• PARAM_NAME_MAP declares key renames.
• SKIP_PATTERNS declares intentionally dropped training-only keys.
• tensor split/fuse helpers are named by operation, e.g. split_qkv.
• build_component_configs(...) writes loader-compatible config files. Most model components use config.json; schedulers use scheduler_config.json.
• build_model_index(...) writes a root model_index.json matching the target FastVideo pipeline and component classes.
• verification reports missing, unexpected, skipped, unchanged, renamed, and shape-mismatched keys.

model_index.json library tokens must match FastVideo loaders:

• standard native DiT/VAE/audio/vocoder/upsampler components loaded by existing Diffusers-style loaders usually use "diffusers" with a FastVideo _class_name in the component config.json;
• text encoders, tokenizers, image encoders, processors, and feature extractors usually use "transformers";
• conditioner currently expects "fastvideo";
• use fully qualified "fastvideo.<module>" only when intentionally relying on the custom fastvideo-library escape path;
• do not write bare "fastvideo" for transformer, VAE, or other loaders that expect "diffusers" unless the loader explicitly expects it.

Mapping Rules

• Use Phase 4 key/shape dumps to derive mappings. Do not guess from official key names alone.
• Preserve each component's official file paths, parity test path, and prototype concerns in comments or structured constants near the mapping that uses them.
• Every official inference parameter should be mapped, copied through, or listed as intentionally skipped with a reason.
• Every FastVideo prototype parameter should receive a tensor or be listed as an intentional external/passthrough parameter.
• Shape matches are necessary but not sufficient; check semantic pairing for Q/K/V, gate/up/down, norm scale/bias, LoRA/base, and modality-specific heads.
• If official and FastVideo fuse or split tensors differently, convert tensors in the script rather than changing production code to match checkpoint quirks.

Verification

Run conversion locally, then verify before returning to Phase 6. For retry requests, update the mapping, rerun conversion, and refresh only the implicated converted component when safe; otherwise rerun the full conversion.

python scripts/checkpoint_conversion/<family>_to_diffusers.py \
    --src <official_weights> \
    --revision <hf_revision> \
    --dst converted_weights/<model_family>

Omit --revision for local sources or when prep recorded default / none.

Minimum output layout:

converted_weights/<family>/
  model_index.json
  transformer/config.json
  transformer/*.safetensors
  vae/config.json
  vae/*.safetensors
  scheduler/scheduler_config.json as needed
  text_encoder/... as needed

Required checks:

• model_index.json exists and lists every required component.
• Each converted component has the config filename its loader expects and safetensors weights when it owns weights. Scheduler dirs require scheduler_config.json; most other native model dirs use config.json.
• Weight filenames may vary by loader: transformer and VAE loaders glob all *.safetensors; text encoders may load *.safetensors, *.bin, and sometimes *.pt; conditioner currently expects diffusion_pytorch_model.safetensors. Use the loader's actual accepted layout rather than assuming one global filename.
• Passthrough components are copied or referenced deliberately.
• Each emitted component config validates through the same path production loaders use. Instantiate the relevant config and call update_model_arch(...) or update_model_config(...) with the emitted JSON so unknown keys fail during conversion, not at pipeline load time.
• Record production loader strictness for every stateful component. If the loader intentionally uses non-strict loading, add explicit missing/unexpected-key assertions in the parity test and document exactly which keys are allowed.
• Each new FastVideo component strict-loads converted weights where its production loader is strict. If strict loading is impossible, record the exact allowed missing/unexpected keys and why they are not inference weights.
• Retry fixes include the original component parity evidence and the new strict-load result in local_tests_readme so the component subagent can resume without rediscovering context.
• local_tests_readme records the command, output directory, and strict-load result.

Do not chase numerical parity in this skill except to identify a conversion mapping bug. Long parity-debug loops belong to /add-model Phase 6.

Escape Hatches

Follow ../add-model/shared/common_rules.md. Conversion-specific ask cases include selecting between incompatible official checkpoints, publishing/uploading weights, overwriting an existing converted repo not created by this run, accepting non-strict missing inference weights, or dropping a component/output from scope.

Handoff

Return ../add-model/contracts/conversion_handoff.md and update the shared state files before handoff.