service-fs — the WORM ledger 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 — this same structural narrowness is what lets the compliance posture below follow from architecture, not from configurable controls.
Key takeaways
service-fsis a WORM ledger, not a filesystem. The implemented API surface is two operations:appendand health. Theread_since,checkpoint, and proof operations are planned. (Correction, 2026-08-02, verified against canonicalorigin/main: this understates real capability —src/http.rsalso registers/v1/checkpoint,/v1/entries,/v1/contract, and/mcpas real, implemented routes, not planned. Flagged, not resolved.)- The ledger is per-tenant — each Totebox holds its own isolated ledger; no cross-tenant reads are possible at the storage layer.
- Compliance with SEC Rule 17a-4(f), eIDAS, and SOC 2 follows from architectural properties, not configurable controls: the storage engine physically lacks the ability to delete or modify records.
- Recurring Sigstore Rekor anchoring by FS anchor emitter creates an external, publicly verifiable timestamp chain for the entire ledger. Verified live: the
local-fs-anchor.timersystemd unit is active and runs monthly (confirmed against the running system). - Tenant isolation via microkernel-level capability-based security is the intended seL4 deployment target, not the current one — today's isolation is process-level, under a standard Linux/BSD daemon.
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
moduleIdboundaries. - 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.
- 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/appendandGET /healthz. - 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
The target durability format is open standards:
- C2SP tlog-tiles: An open-standard text-based format ensuring 100-year readability, allowing future archivists to decode storage using standard Unix utilities without proprietary software or vendor assistance.
- C2SP signed-note Checkpoints: Compact, signed artifacts that prove the state of the ledger at any point in time.
The tile backend is planned; the current build uses a per-tenant JSON append log with per-payload SHA-256 digests. An Audit-Log Sub-Ledger — a dedicated WORM ledger that records every read event — satisfies SOC 2 processing integrity requirements independently of the tile format's completion.
Regulatory alignment and compliance
service-fs's security posture is not a policy layer but a fundamental architectural property, designed to satisfy multiple international regulatory frameworks:
- SEC Rule 17a-4(f): The platform targets the strict "WORM path," structurally denying record modification. This exceeds the "audit-trail" alternative often used by cloud vendors to mask mutable underlying storage.
- eIDAS (EU 2025/1946): Aligns with Qualified Preservation standards, ensuring long-term integrity, authenticity, and accessibility "irrespective of future technological changes."
- SOC 2 Trust Services Criteria: Directly addresses Processing Integrity (PI1, PI4) through signed ingest and read-audit sub-ledgers, and Logical Access (CC6) via tenant-level isolation.
Three structural properties underpin this posture:
- Structural immutability. The Rust API surface and underlying storage engine physically lack the ability to delete or modify records.
- Merkle-chain integrity. Every entry is cryptographically linked to the next using Merkle consistency proofs; any attempt to alter history is instantly detectable.
- External witnessing. Monthly anchoring to the Sigstore Rekor public log by FS anchor emitter provides a proof-of-state independent of the platform's own internal systems.
Tenant isolation is the one property still in progress: in the intended seL4 deployment, isolation is enforced by microkernel-level capability-based security, making cross-tenant access mathematically impossible. Today, under Envelope A, isolation is process-level under standard Linux/BSD daemon boundaries — a real but weaker guarantee than the seL4 target.
Threat model mitigation
- Operator tampering. Even an administrator with root access cannot alter the ledger without breaking the Merkle chain and failing public Rekor consistency checks. The machine-based authentication system prevents unauthorised signing.
- Vendor obsolescence. Open-standard formats ensure data survival beyond the lifespan of the software vendor.
- Cryptographic agility. The system is designed to transition to post-quantum signature schemes (e.g., Dilithium) without requiring a full storage migration.
See also
- FS anchor emitter — the periodic anchor emitter that checkpoints the ledger to Sigstore Rekor
- WORM ledger substrate: four-layer architecture and two boot envelopes — infrastructure-level WORM architecture
- WORM ledger design — the design philosophy behind the WORM approach
- seL4 microkernel substrate — the seL4 Microkit envelope (Envelope B) that is the intended runtime
- Capability-based security — the microkernel-level isolation mechanism targeted for Envelope B
- Machine-based authorization — the authentication system that prevents unauthorised signing
- service-content — entity extraction and knowledge-graph host — the Gravity Engine that writes L0 base geometry records to service-fs
- PointSav Link Service — hot-pluggable adapter connecting os-* nodes to the fleet fabric