feat: provide a TableTheory-backed FaceTheory ISR MetaStore (so FaceTheory can drop DynamoDbIsrMetaStore)

[aron23]

Motivation
FaceTheory currently ships a DynamoDB-shaped ISR store (DynamoDbIsrMetaStore + DynamoDbIsrMetaClient) in FaceTheory/ts/src/isr.ts. Even though it doesn’t import the AWS SDK directly, it effectively pushes DynamoDB conditional-write semantics into FaceTheory/app code.

We want a stricter layering rule: all DynamoDB access patterns and conditional expressions live in TableTheory.

Goal
Add a small, first-class helper in TableTheory (TS first) that implements FaceTheory’s ISR metadata + lease/lock operations using TableTheory primitives, so FaceTheory apps don’t implement DynamoDB calls themselves.

References

• Schema + transaction recipes already exist:
  • docs/facetheory/isr-cache-schema.md
  • docs/facetheory/isr-transaction-recipes.md
• FaceTheory ISR store interface:
  • FaceTheory/ts/src/isr.ts (IsrMetaStore)

Proposed API (TS)
One of:

• new FaceTheoryIsrMetaStore({ client: TheorydbClient, tableName, ... }) OR
• createFaceTheoryIsrMetaStore(...)

Implement methods compatible with FaceTheory’s IsrMetaStore shape:

• get(cacheKey)
• tryAcquireLease({ cacheKey, leaseOwner, nowMs, leaseDurationMs, ... })
• commitGeneration({ cacheKey, leaseOwner, leaseToken, htmlPointer, generatedAt, ... })
• releaseLease({ cacheKey, leaseOwner, leaseToken }) (best-effort)

Implementation sketch

• Use the existing LeaseManager for LOCK rows.
• Use TheorydbClient.transactWrite() for the “publish META + release LOCK” atomic step (Recipe A in the docs).
• Map FaceTheory’s cacheKey to TableTheory’s pk; use sk values META and LOCK as in the docs.

Acceptance Criteria

• TableTheory exports a supported TS helper for FaceTheory ISR metadata/leases.
• Unit + DynamoDB Local integration tests exist (similar rigor to LeaseManager tests).
• A short doc section shows how a FaceTheory app wires this store, including env var FACETHEORY_CACHE_TABLE_NAME.

Follow-up (FaceTheory)
Once this exists, FaceTheory can deprecate/remove DynamoDbIsrMetaStore / DynamoDbIsrMetaClient and point users to the TableTheory implementation.

[aron23]

Implemented in PR #73 (base: staging).

[aron23]

Verified in TableTheory v1.4.0: ships FaceTheoryIsrMetaStore (ts/src/facetheory-isr.ts), exported from the TS package, with unit+integration coverage and docs updates.