TASK-002B: File-Backed History Store

• Status: Ready
• Parent: TASK-002
• Spec: SLICE-002
• Depends on: TASK-002A

AI Execution Profile

• Model class: Balanced
• Reasoning effort: Medium

Scope

• implement file-backed JSON history storage in infrastructure
• make the file path configurable
• support load-all and append-or-upsert behavior by RunId
• define safe behavior for missing files and corrupted content

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Implement only TASK-002B: File-Backed History Store.

Read first:
- docs/specs/SLICE-002-persistent-run-history.md
- docs/adrs/ADR-002-file-backed-run-history-store-before-database-persistence.md
- docs/tasks/slice-002/TASK-002B-file-backed-history-store.md

Goal:
- Implement the infrastructure-side JSON file-backed run history store.

Scope:
- Implement configurable-path file storage.
- Support loading existing history.
- Support append or upsert by RunId.
- Handle missing files gracefully.
- Surface corrupted or unreadable content as a recoverable failure path.

Do not:
- Wire startup hydration yet
- Wire workflow persistence yet
- Build UI yet

Important:
- Keep the implementation behind the application abstraction
- Keep behavior testable with temporary files