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FS architecture and the WORM backbone

Every record written to the PointSav platform — identity anchors, email communications, document artifacts — lands in service-fs, a per-tenant Write-Once-Read-Many (WORM) immutable ledger. Once written, records cannot be modified or deleted; the ledger is the tamper-evident backbone that Ring 2 services query and Ring 1 services write to. For a regulated operator, this means every data event has a provable, auditable history from the moment it enters the platform. The worm-ledger-design article describes the WORM design philosophy in detail.

service-fs is not a general-purpose filesystem. A local filesystem permits reads, writes, modifications, and deletions through a standard directory tree. service-fs exposes three operations only: append (add a record), read_since (read forward from a checkpoint), and checkpoint (create a signed proof of state). The narrowed API surface is what makes the ledger's integrity guarantees structurally sound rather than policy-enforced.

The Four-Layer Architecture

To ensure modularity and survivability, service-fs is implemented as a decoupled four-layer stack:

  • L4: Anchoring (Workspace-Tier): Monthly periodic work performed by fs-anchor-emitter that anchors signed checkpoints to the public Sigstore Rekor log.
  • L3: Wire Protocol: The communication interface (HTTP/axum today; MCP long-term) that enforces per-tenant moduleId boundaries.
  • L2: WORM Ledger API (Rust Trait): The stable core contract (append, read_since, checkpoint) that survives changes to the layers above or below.
  • L1: Tile Storage Primitive: The envelope-specific storage engine (POSIX on Linux; capability-mediated on seL4) using the C2SP tlog-tiles format.

Dual Boot Envelopes

service-fs is designed to operate across two runtime envelopes from one codebase. The WORM storage architecture article describes the intended storage model for each envelope.

  1. Envelope A (Current): A Linux/BSD daemon under systemd. It uses standard POSIX file I/O and process isolation. This is the only implemented envelope; it exposes POST /v1/append and GET /healthz.
  2. Envelope B (seL4 — deferred): A verified seL4 Microkit Protection Domain is the planned future target. It is intended to use moonshot-database (PSDB) for capability-addressed storage, providing formally verified tenant isolation. Envelope B exists only as a reference entry point (main_sel4_stub.rs) that is not compiled into the current build.

Durability and Compliance

The platform achieves structural WORM compliance by structurally denying record modification at the storage layer. This is reinforced by:

  • C2SP tlog-tiles: An open-standard text-based format ensuring 100-year readability.
  • C2SP signed-note Checkpoints: Compact, signed artifacts that prove the state of the ledger at any point in time.
  • Audit-Log Sub-Ledger: A dedicated WORM ledger that records every read event to satisfy SOC 2 processing integrity requirements.

This architecture ensures that service-fs remains portable, verifiable, and resilient to vendor obsolescence.

Key takeaways

  • service-fs is a WORM ledger, not a filesystem. The implemented API surface is two operations: append and health. The read_since, checkpoint, and proof operations are planned.
  • The ledger is per-tenant — each Totebox holds its own isolated ledger; no cross-tenant reads are possible at the storage layer.
  • The four-layer architecture is designed to decouple wire protocol, API contract, and storage engine, so the seL4 Envelope B swap does not require rewriting the service.
  • The target durability format is open standards: C2SP tlog-tiles (100-year readability) and C2SP signed-note Checkpoints (compact provability). The tile backend is planned; the current build uses a per-tenant JSON append log with per-payload SHA-256 digests.
  • Recurring Sigstore Rekor anchoring by fs-anchor-emitter is intended to create an external, publicly verifiable timestamp chain for the entire ledger. The anchoring operation is planned and not yet running.

See also

Important Information

Important Information

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