Replay Guarantees

Fabra uses “replay” in an incident sense: make a decision reconstructable.

This page defines what is guaranteed vs best-effort so you can rely on it under pressure.

Two concepts: show vs replay

Show (guaranteed if the record exists)

fabra context show returns the stored artifact for audit/debugging.

This answers: “what did the system record at decision time?”

Replay (best-effort execution)

POST /v1/context/{id}/replay?timestamp=... re-executes the context function when possible.

This answers: “if we re-run the assembly, what happens?”

Guarantees

Feature time-travel (guaranteed when supported)

When you replay with a timestamp, Fabra will retrieve feature values as of that timestamp (requires an offline store that supports historical reads).

Lineage + budgeting

Dropped items and budget decisions are recorded as part of lineage/record metadata and can be inspected later.

Best-effort (explicitly not guaranteed)

Retriever determinism

External retrievers (vector DBs, web, SaaS) can change.

Fabra can provide:

• Evidence replay: the recorded retrieved items/metadata (what the system recorded)
• Re-query replay: re-running the retriever against a changing index (not deterministic by default)

If you need strict reproducibility for retrieval, treat retrieval content as part of the durable artifact (and store it intentionally).

Code drift

Replay re-executes current code unless you pin code version. If you deploy new context logic, replay may differ even for the same inputs.

Practical incident guidance

• Use show + diff to settle “what changed?” quickly.
• Use verify when audits/disputes demand tamper-evidence.
• Use replay for confirming hypotheses, not as the only source of truth.