Image identity hashes every COPY source, so a `COPY . .` Containerfile marks outputs stale on any new file

[rpaviot]

What happened

code_version folds in lightcone.engine.container.image_identity, a content hash of the Containerfile's
COPY sources. With the scaffolded COPY . . this includes everything in the project not excluded by
directory name (.git/.venv/results/.lightcone/.snakemake/pycache), so a new SLURM log file in logs/,
a README edit or a notebook changed the identity between two runs: Snakemake reported "Params have
changed", deleted a finished 10-minute fit and re-ran it, and lc status flipped all outputs to stale.
Nothing in the output tells the user which file changed the hash.

Reproduction

1. Scaffolded project with the default COPY . . Containerfile, runtime: none.
2. lc run output_a (ok).
3. touch logs/anything.out (or edit README.md).
4. lc status -> output_a is stale; lc run output_a re-runs it.

Workaround used: COPY only src/ config/ scripts/ and keep job logs under results/. A default
.dockerignore-style exclusion of logs/docs, or a status line naming the changed COPY source, would help.

Environment

• ASTRA: 0.2.11
• lightcone-cli: 0.4.2
• Python: 3.12.8
• OS: Linux 4.18 (RHEL 8, SLURM cluster, container runtime: none)