[leifdenby]

Lets a run be continued instead of restarted, e.g. to train the DMI ConvGRU run intrigued-sow-455 beyond its 22 h.

What it adds

• Experiment.ckpt_path, passed to Trainer.fit(ckpt_path=...) (Lightning 2.x has no Trainer-level resume argument). Restores weights, optimizer, LR scheduler, step counter and the max_time timer, so max_time is the total budget.
• resume_training fiddler (ckpt_path, optional mlflow_run_id): sets the above; with a run id the MLflow logger keeps logging into that run, so the metric curves continue.
• mlcast train --config mlflow:<run>: accepts a run id, runs:/<id> or the run URL from the MLflow UI (which also gives the tracking server). Downloads the run's config/*.yaml and its latest checkpoint (highest step=N) into .mlcast-resume/<run_id>/, seeds the config from the YAML and applies resume_training; your set:/fiddler: overrides apply on top.
• Checkpoint upload: use_mlflow_logger now sets log_model="all", so every checkpoint is uploaded to the run as it is saved (~770 MB each for the 5-block ConvGRU) and runs can be resumed from any machine. For runs from before this, the local <experiment_id>/<run_id>/checkpoints is used.
• The config artifact is now config/config.yaml (it was a random temp-file name, although the log message already said config/config.yaml), so a resumed run replaces it instead of adding a second YAML.

Example

mlcast train \
    --config mlflow:https://mlflow.dmidev.org/#/experiments/114/runs/52dd4f17fad94d2eb0ac8489c234f6c2 \
    --config 'set:trainer.max_time="03:00:00:00"'

Testing

• tests/config/test_mlflow_resume.py (22 tests): run-reference parsing, latest-checkpoint choice from artifacts and the local fallback, reuse of an existing download, the fiddler, Experiment.run passing ckpt_path, CLI token extraction. Full suite: 169 passed, 5 skipped.
• End to end against a local MLflow file store: trained 20 steps, then --config mlflow:<run> with max_epochs=2 downloaded the step-20 checkpoint, Lightning restored all states, and training continued to step 40 in the same MLflow run, uploading the new checkpoint.
• docs/config_diagram.svg is unchanged: regenerating it locally gives the same labels; only the local Graphviz (12.2.1 vs CI's 2.43.0) renders differently, so that hook was skipped for the commit.

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