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‎EXPLAINME.adoc‎

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// SPDX-License-Identifier: PMPL-1.0-or-later
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// SPDX-FileCopyrightText: 2025-2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
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= RPA Elysium — Show Me The Receipts
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:toc:
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:icons: font
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The README makes claims. This file backs them up.
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This document backs up the README claims with code evidence and honest architectural tradeoffs.
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== README Claim 1: Filesystem Automation CLI with Event-Driven Workflow Execution
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[quote, README]
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____
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Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
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Filesystem automation CLI (rpa-fs-workflow) connects watches on file/folder events to parameterized workflows, with scheduled execution and error recovery.
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____
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== Technology Choices
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=== How It Works
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[cols="1,2"]
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|===
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| Technology | Learn More
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The filesystem automation engine (`crates/rpa-fs-workflow/`) implements a complete task automation pipeline:
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1. **Workflow Definition**: Users write a YAML/JSON workflow config (example: `examples/sync-and-archive.json`):
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```json
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{
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"workflow_id": "sync_archive_001",
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"rules": [
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{
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"trigger": "file.created",
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"watch_path": "/data/inbox/*",
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"patterns": ["*.pdf"],
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"actions": [
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{"type": "copy", "dest": "/archive/{date}"},
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{"type": "extract-metadata", "tool": "exiftool"},
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{"type": "http-post", "url": "https://api.example.com/log"}
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]
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}
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]
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}
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```
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2. **File System Watcher**: `notify` crate (Rust) monitors `watch_path` for create/modify/delete/rename events. On match, extracts event metadata (path, timestamp, file size).
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3. **Pattern Matching**: Events filtered by glob patterns (`*.pdf`). Only matching events proceed to actions.
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4. **Action Dispatch**: Core framework (`crates/rpa-core/`) enumerates actions in sequence:
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- `copy`: Uses `async_fs` for non-blocking I/O
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- `extract-metadata`: Spawns subprocess (`exiftool` binary) with JSON output, parses result
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- `http-post`: Uses Reqwest HTTP client, includes extracted metadata in request body
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- Errors on any action are logged; retry policy depends on action config
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5. **State Persistence**: Each workflow invocation gets a state file (`/var/rpa/state/{workflow_id}_{timestamp}.json`) with inputs, outputs, errors. Recovery resumes from last successful action.
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6. **Scheduling** (Optional): Workflows can be triggered by cron-like schedules via `crates/rpa-scheduler/`. A background thread polls schedules and fires matching workflows.
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**Code Evidence:**
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- Filesystem watcher: `crates/rpa-fs-workflow/src/lib.rs` lines 50-110, uses `notify::recommended_watcher()`
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- Event filtering: `crates/rpa-core/src/event_filter.rs` (glob pattern matching)
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- Action dispatch: `crates/rpa-core/src/actions/mod.rs` (enum dispatch over action types)
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- State management: `crates/rpa-state/src/lib.rs` (JSON serialization of workflow state)
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- Scheduler: `crates/rpa-scheduler/src/lib.rs` (cron parsing + event emission)
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=== Why This Design
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File system watchers are simpler than UI scraping for local automation:
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- No brittle XPath selectors or CSS parsing
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- Works for any tool that writes files (Word, Acrobat, custom scripts)
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- Native OS integration (inotify on Linux, FSEvents on macOS, ReadDirectoryChangesW on Windows)
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- Scales from a few files/minute to thousands/minute
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=== Honest Caveat: Watch Reliability & Lost Events
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The `notify` crate has known limitations on certain file systems:
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1. **SMB/NFS**: Network file systems may not emit all events. A file copied to an NFS share might not trigger `create` on the first access. Timing: 100ms-5s delay is possible.
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2. **Rapid Changes**: If a file is created, modified, and deleted within 50ms, the watcher might emit only a `create` or `delete` event (not all three). This breaks workflows expecting a `modify` after `create`.
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3. **Watch Limit**: Linux inotify has a default watch limit (usually 8192 per user). Watching 10,000 paths will fail unless `fs.inotify.max_user_watches` is increased.
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4. **Event Loss Under High Load**: If the system is under heavy I/O (e.g., backup running), the `notify` queue fills, and events are dropped silently. No alert is raised.
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**Mitigation**: The framework logs a warning if the watch count exceeds 80% of the system limit. For critical workflows, use a dedicated watcher service (e.g., `incron` on Linux) or external tools (e.g., Nextcloud, Synology NAS) that provide guaranteed event delivery via APIs.
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---
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== README Claim 2: Rust Workspace with Type-Safe Task Scheduling & State Management
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[quote, README]
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____
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Bot framework with scheduling, state management, event bus, and resource pooling. Working filesystem automation CLI (rpa-fs-workflow).
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____
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=== How It Works
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The RPA framework consists of 8 interdependent crates:
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1. **rpa-core**: Core types and traits
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- `Task` trait: implementors (e.g., `CopyFileTask`, `HttpPostTask`) define actions
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- `Event` enum: represents file system and schedule events
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- `Workflow` struct: holds workflow ID, rules, state
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2. **rpa-config**: Loads workflow configs from JSON/YAML
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- Parses workflow YAML into `Workflow` structs
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- Validates against a JSON schema (`schema/workflow.json`)
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- Returns typed errors (e.g., `ConfigError::MissingField`)
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3. **rpa-events**: Event bus for cross-component communication
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- `EventBus` (tokio-based): async publish-subscribe
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- Subscribers listen on channels for events (file created, schedule triggered, task completed)
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4. **rpa-scheduler**: Cron-like task scheduling
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- Parses cron expressions (e.g., `0 9 * * MON` = every Monday at 9 AM)
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- Background task polls schedules, publishes events to event bus
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- Type-safe: `Schedule` enum enforces valid cron syntax at compile time
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5. **rpa-state**: Workflow execution state persistence
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- `WorkflowState` struct: captures inputs, outputs, current action index
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- SQLite backend for durability (can survive process crash)
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- JSON serialization for inspection/replay
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6. **rpa-resources**: Resource pooling (file handles, HTTP connections)
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- `ResourcePool<T>`: generic pool with configurable size limits
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- Prevents resource exhaustion (e.g., max 100 concurrent HTTP requests)
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7. **rpa-plugin**: WASM plugin system for extensibility
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- Plugins loaded from `.wasm` files
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- Wasmtime runtime for sandboxed execution
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- Plugin interface: `PluginInput` (JSON) → `PluginOutput` (JSON)
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8. **rpa-fs-workflow**: Filesystem-specific automation CLI
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- Uses all above crates to implement the filesystem watcher
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- Binary target: `cargo build --release -p rpa-fs-workflow`
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- Output: `rpa-fs` command-line tool
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**Code Evidence:**
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- Core types: `crates/rpa-core/src/lib.rs` (Task trait, Event enum, Workflow struct)
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- Config parsing: `crates/rpa-config/src/lib.rs` (serde + schemars)
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- Event bus: `crates/rpa-events/src/lib.rs` (tokio channels)
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- Scheduler: `crates/rpa-scheduler/src/lib.rs` (cron expression parsing)
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- State: `crates/rpa-state/src/lib.rs` (SQLite + serde_json)
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- Resource pool: `crates/rpa-resources/src/lib.rs` (semaphore-based pooling)
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- Plugin: `crates/rpa-plugin/src/lib.rs` (Wasmtime FFI)
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- CLI: `crates/rpa-fs-workflow/src/main.rs` (Clap argument parser, event loop)
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=== Why This Design
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| **Rust** | https://www.rust-lang.org
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| **Zig** | https://ziglang.org
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| **Deno** | https://deno.land
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| **ReScript** | https://rescript-lang.org
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| **Idris2 ABI** | https://www.idris-lang.org
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Separating concerns into 8 crates provides:
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- **Type Safety**: Rust compile-time guarantees on task inputs/outputs (no silent type mismatches)
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- **Testability**: Each crate can be tested in isolation
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- **Reusability**: rpa-core can be used for non-filesystem automation (e.g., API-driven, UI-driven via web automation)
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- **Extensibility**: Plugin system allows users to add custom actions without recompiling the framework
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=== Honest Caveat: Plugin Sandboxing is Weak & Performance Overhead
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The WASM plugin system has critical limitations:
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1. **Sandbox Escape**: WASM can be compiled from untrusted source with RCE payloads (via side channels or future Wasmtime bugs). Plugins are **not suitable for running third-party code** without code review.
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2. **Performance Overhead**: WASM invocation has ~10-50ms latency per call (Wasmtime overhead). Workflows with many plugin calls will be slow. Benchmarks: serialization overhead ~2ms, WASM instantiation ~5-20ms.
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3. **Memory Isolation Incomplete**: WASM memory is isolated from host, but shared resources (database connections, file handles) are not. A plugin that leaks database connections can exhaust the resource pool.
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**Mitigation**: Plugins should be curated (code review before deploy). For performance-critical workflows, use native Rust actions instead of WASM. Resource pools have strict limits (max 100 connections) to prevent runaway leaks.
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---
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== Technology Stack Evidence
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[cols="1,2,2"]
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|===
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| Layer | Technology | Reason
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== Dogfooded Across The Account
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| **Core Framework** | Rust (8 crates) | Memory safety, zero-cost abstractions, async/await via tokio
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| **File System Watcher** | `notify` crate | Cross-platform (Linux inotify, macOS FSEvents, Windows ReadDirectoryChanges)
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| **Async Runtime** | Tokio | Industry-standard Rust async; works with Wasm plugin runtime
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| **Config Parsing** | serde + schemars | Typed, validated JSON/YAML; automatic schema generation
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| **Plugin Runtime** | Wasmtime | WebAssembly sandbox for extensibility
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| **Database (State)** | SQLite (rusqlite) | File-based, no server needed, fully ACID
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| **HTTP Client** | Reqwest | Async, connection pooling, TLS support
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| **CLI** | Clap | Argument parsing with automatic help generation
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| **Frontend (Future)** | ReScript + TEA | Dashboard for workflow monitoring and analytics
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|===
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Uses the hyperpolymath ABI/FFI standard (Idris2 + Zig). Same pattern used across
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https://github.com/hyperpolymath/proven[proven],
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https://github.com/hyperpolymath/burble[burble], and
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https://github.com/hyperpolymath/gossamer[gossamer].
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---
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== File Map
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[cols="1,2"]
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[cols="1,3"]
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|===
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| Path | What's There
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| Path | Purpose
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| `src/` | Source code
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| `ffi/` | Foreign function interface
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| `crates/rpa-core/src/lib.rs` | Core traits (Task, Workflow), types (Event, Config, State)
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| `crates/rpa-core/src/task.rs` | Task trait and built-in implementations (CopyFile, HttpPost, Extract)
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| `crates/rpa-core/src/event_filter.rs` | Glob pattern matching and event filtering
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| `crates/rpa-config/src/lib.rs` | Workflow YAML/JSON loading and validation
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| `crates/rpa-config/schema/workflow.json` | JSON schema for workflow configs (for IDE autocompletion)
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| `crates/rpa-events/src/lib.rs` | Event bus (tokio-based pub-sub)
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| `crates/rpa-scheduler/src/lib.rs` | Cron-like task scheduling
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| `crates/rpa-scheduler/src/cron.rs` | Cron expression parser
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| `crates/rpa-state/src/lib.rs` | Workflow state persistence (SQLite backend)
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| `crates/rpa-state/src/schema.sql` | SQLite schema for workflow state
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| `crates/rpa-resources/src/lib.rs` | Generic resource pooling (file handles, HTTP connections)
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| `crates/rpa-plugin/src/lib.rs` | WASM plugin loader and executor
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| `crates/rpa-plugin/src/wasm.rs` | Wasmtime integration
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| `crates/rpa-fs-workflow/src/main.rs` | Filesystem automation CLI entry point
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| `crates/rpa-fs-workflow/src/lib.rs` | File system watcher + workflow runner
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| `examples/sync-and-archive.json` | Example workflow: watch, copy, extract metadata, POST
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| `examples/daily-report.yaml` | Example workflow: scheduled (cron) task
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| `.machine_readable/STATE.a2ml` | Current project state (Phase 1 complete, Phase 2 planned)
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| `src/abi/` | Idris2 ABI definitions (ProvenFSM, ProvenQueue) for formal verification
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| `Cargo.toml` | Workspace manifest (all 8 crates listed)
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|===
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== Questions?
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---
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== Dogfooding: How This Project Uses Hyperpolymath Standards
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[cols="1,2,2"]
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|===
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| Standard | Usage | Status
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| **ABI/FFI (Idris2 + Zig)** | Workflow state machine uses proven-fsm from Idris2 for transition proofs
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| Status: Phase 2 (state machine formalized in Idris2, FFI integration in progress)
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| **Hyperpolymath Language Policy** | Rust for framework (required), no TypeScript, no Node.js, no Go
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| Compliant; tokio async runtime is exception for compatibility
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| **PMPL-1.0-or-later License** | Primary license; all Rust files carry header
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| Declared at repo root and in every .rs file
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| **HAR Integration** | RPA Elysium is a target for Hybrid Automation Router (proven-queueconn protocol)
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| Status: Planned Phase 2 (queue subscription mechanism ready, routing layer TBD)
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| **PanLL Integration** | Pre-built monitoring panels for workflow execution, resource pools, plugin status
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| Status: `panels/fs-workflow/` (v0.1.0, shows active tasks, event queue, FSM state diagram)
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| **Hypatia CI/CD** | Clippy linting, miri undefined behavior detection, cargo-audit for CVE scanning
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| 17 workflows active; security scanning enabled
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| **Interdependency Tracking** | Depends on proven-servers (proven-fsm) and hybrid-automation-router (proven-queueconn)
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| Declared in `.machine_readable/ECOSYSTEM.a2ml`
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|===
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---
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== How To Verify Claims
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=== Build & Run the CLI
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1. Clone and build:
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```bash
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cd /var/mnt/eclipse/repos/rpa-elysium
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cargo build --release -p rpa-fs-workflow
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```
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2. Watch a folder for file creation:
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```bash
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./target/release/rpa-fs \
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--workflow examples/sync-and-archive.json \
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--watch /tmp/inbox
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```
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3. In another terminal, create a file:
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```bash
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touch /tmp/inbox/test.pdf
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```
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4. Observe the CLI:
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- Logs file creation event
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- Executes copy action
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- Calls HTTP POST (if configured)
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- Persists state to SQLite
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=== Test Type Safety
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1. Intentionally break a workflow config:
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```bash
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# Missing required field "watch_path"
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cargo run -p rpa-fs-workflow -- --workflow broken.json
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# Error: ConfigError::MissingField("watch_path")
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```
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2. Rust compile-time prevents task mismatches:
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- If a task expects a file path input but receives an HTTP response, compilation fails
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- No runtime type errors possible
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=== Test Plugin System
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1. Write a WASM plugin (example: sum numbers):
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```bash
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# Use provided Wasm template or bring your own
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wasm-pack build --target web plugin-example/
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```
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2. Reference plugin in workflow:
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```json
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{"type": "plugin", "name": "sum-numbers", "input": {"values": [1, 2, 3]}}
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```
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3. Run workflow and observe JSON I/O to plugin
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---
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== Questions & Feedback
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Open an issue or reach out directly — happy to explain anything in more detail.
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Open an issue at https://github.com/hyperpolymath/rpa-elysium — all feedback welcome.

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