#918 model evaluate is slow resolving data.latest expressions in large datastores

Summary

swamp model evaluate can spend ~30-35s at expression evaluation for a single model that contains only a few data.latest(...) expressions, even when reading the referenced data directly takes ~1s.

This appears to be a performance bug in model expression evaluation: resolving a targeted data.latest(modelName, dataName) expression seems to pay a broad datastore/catalog scan cost, possibly repeated per expression, rather than using the direct data lookup path.

Reproduction

A model has global arguments like:

globalArguments:
  host: ${{ data.latest("lab-vm-pool", "vaultwarden").attributes.ipAddress }}
  user: ${{ data.latest("lab-vm-pool", "vaultwarden").attributes.bootstrapSSHUser.username }}
  hostKeyPath: ${{ data.latest("lab-vm-pool", "vaultwarden").attributes.sshHostCertificate.hostKeyPath }}

Timing the evaluation:

time swamp model evaluate vaultwarden-host-key --json

Observed: about 30-35 seconds, with high memory usage observed around 2GB RSS in one run.

But the directly referenced data is fast to retrieve:

time swamp data get lab-vm-pool vaultwarden --json >/tmp/vw.json

Observed: about 1 second.

The repository has a large .swamp/data tree, including multi-GB data for unrelated models. The referenced lab-vm-pool/vaultwarden data itself is small.

Expected behavior

data.latest("lab-vm-pool", "vaultwarden") during model evaluation should use an indexed/direct lookup comparable to swamp data get lab-vm-pool vaultwarden, and should not scan or load unrelated data. Multiple references to the same data item in one model evaluation should also ideally be cached within the evaluation.

Actual behavior

swamp model evaluate takes ~30-35s at expression evaluation, while the target data lookup takes ~1s.

Environment

Current swamp version:

20260630.112427.0-sha.0e5078e9

swamp update --check --json reports a newer version is available (20260702.171037.0-sha.ca29630a), but source-version comparison was inconclusive because swamp source fetch --version 20260702.171037.0-sha.ca29630a failed in this environment with Read-only file system (os error 30): mkdir '/var/home/<USERNAME>/.swamp/source'.