Experiment with gh-aw resources for Cast validator transport #1982

Goal

Validate that gh-aw resources: can transport Squad's Cast validator as a reviewable plaintext sidecar while preserving the existing direct workflow installation path and disk-only execution model.

Scope

This is a gh-aw-only test/experiment for the new test zone. It must have no bearing on Squad CLI or SDK installation, packaging, runtime, or distribution behavior. Do not modify packages/squad-cli/ or packages/squad-sdk/.

Proposed experiment

• Add a minimal plaintext probe resource declared by the top-level workflows/squad.md.
• Assert during the pre-agent phase that the installed resource is present, readable, and matches a pinned SHA-256.
• Preserve the existing Base64 Cast validator and execution path for this experiment so casting behavior remains unchanged if the probe passes.
• Compile with the repository-pinned gh-aw version in strict mode and regenerate the corresponding lock output.
• Add focused tests proving the resource declaration, runtime check, digest handling, and gh-aw-only scope.
• Document how to install/update the experimental dev workflow in a test repository and rerun /squad cast.

Acceptance criteria

• A fresh or updated gh aw add bradygaster/squad/workflows/squad.md@dev installation carries the probe resource into the consumer repository.
• The workflow fails clearly if the probe is missing, unreadable, or has the wrong digest.
• Existing Cast validation remains intact and continues using the current payload during the experiment.
• No CLI/SDK source, package manifest, installation documentation, or distribution path changes.
• PR targets dev, is clearly labeled as an experiment, and is left for human review and merge.

Follow-up if successful

After proving the behavior in the test zone with a second setup and casting call, file or implement a separate change replacing the Base64 validator transport with a plaintext resource while retaining runtime integrity checks.