feat: Add DigestUpsertRequest and LockEntity models

- Introduced DigestUpsertRequest for handling digest upsert requests with properties like ChannelId, Recipient, DigestKey, Events, and CollectUntil.
- Created LockEntity to represent a lightweight distributed lock entry with properties such as Id, TenantId, Resource, Owner, ExpiresAt, and CreatedAt.

feat: Implement ILockRepository interface and LockRepository class

- Defined ILockRepository interface with methods for acquiring and releasing locks.
- Implemented LockRepository class with methods to try acquiring a lock and releasing it, using SQL for upsert operations.

feat: Add SurfaceManifestPointer record for manifest pointers

- Introduced SurfaceManifestPointer to represent a minimal pointer to a Surface.FS manifest associated with an image digest.

feat: Create PolicySimulationInputLock and related validation logic

- Added PolicySimulationInputLock record to describe policy simulation inputs and expected digests.
- Implemented validation logic for policy simulation inputs, including checks for digest drift and shadow mode requirements.

test: Add unit tests for ReplayVerificationService and ReplayVerifier

- Created ReplayVerificationServiceTests to validate the behavior of the ReplayVerificationService under various scenarios.
- Developed ReplayVerifierTests to ensure the correctness of the ReplayVerifier logic.

test: Implement PolicySimulationInputLockValidatorTests

- Added tests for PolicySimulationInputLockValidator to verify the validation logic against expected inputs and conditions.

chore: Add cosign key example and signing scripts

- Included a placeholder cosign key example for development purposes.
- Added a script for signing Signals artifacts using cosign with support for both v2 and v3.

chore: Create script for uploading evidence to the evidence locker

- Developed a script to upload evidence to the evidence locker, ensuring required environment variables are set.

tools/cosign/README.md

@@ -15,3 +15,13 @@
 - v3 DSSE blob: `cosign sign-blob --key cosign.key --predicate-type stella.ops/confidenceDecayConfig@v1 --bundle confidence_decay_config.sigstore.json decay/confidence_decay_config.yaml`
 - v3 verify: `cosign verify-blob --bundle confidence_decay_config.sigstore.json decay/confidence_decay_config.yaml`
 - To force offline fallback, export `PATH=./tools/cosign:$PATH` (ensures v2.6.0 is used).
+
+## CI / secrets
+- CI should provide a base64-encoded private key via secret `COSIGN_PRIVATE_KEY_B64` and optional password in `COSIGN_PASSWORD`.
+- Example bootstrap in jobs:
+  ```bash
+  echo \"$COSIGN_PRIVATE_KEY_B64\" | base64 -d > /tmp/cosign.key
+  chmod 600 /tmp/cosign.key
+  COSIGN_PASSWORD=\"${COSIGN_PASSWORD:-}\" cosign version
+  ```
+- For local dev, copy your own key to `tools/cosign/cosign.key` or export `COSIGN_PRIVATE_KEY_B64` before running signing scripts. Never commit real keys; only `cosign.key.example` lives in git.