72 lines
3.5 KiB
Markdown
72 lines
3.5 KiB
Markdown
# Decisions
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Why Sausage is the way it is. `PROTOCOL.md` and the code own the details.
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When this file disagrees with them, they win.
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## The shape
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- **JSON-RPC, not component interfaces.** Every language can read and write
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lines of JSON, and models know JSON-RPC from LSP and MCP. A call has a
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result, like an LLM tool call.
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- **A process per call.** WASI has no threads, so processes give
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parallelism. A new version applies at the next call, and old processes
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retire after a grace period.
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- **Attached by default.** A process does not outlive its caller by
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accident. A long-running process must ask for `detach`.
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- **Services in one file.** Only the core starts and restarts them, so
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upgrades and singletons need no logic in plugins.
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- **Files to inspect, calls to act.** This keeps the core API small, and the
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agent's file tools are enough to explore the world.
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- **The core accepts only `.wasm` files.** It knows no source language.
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`cargo` is one way to get a `.wasm` file.
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- **The world folder is the source of truth.** Copy a plugin folder into
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another world, and it works there.
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- **The agent is a normal plugin.** It can read and upgrade its own source,
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and change how it does inference.
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## Interfaces
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- **Generated imports and interface checks, without version numbers.** A
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model that translates a description by hand makes errors. A generator does
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not. The check catches the most common error in a world that changes
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itself: a change to one plugin breaks another one.
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- **A small schema subset.** With Draft 7 and a fixed subset, our own check
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can decide every case. It never has to guess.
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- **Docs are part of the interface.** Other agents work from them, so the
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SDK requires a doc comment on each method, type, and field.
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- **The check covers calls, not state.** Old and new versions share
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`/state`. A plugin keeps its state format compatible, or migrates it in
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`rpc.retired`.
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## Minimal on purpose
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The core does only what a plugin cannot do for itself. Everything else can be
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a plugin, or a change that the agent makes to itself.
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- **No permissions, no limits, no hiding.** Any process can call, upgrade,
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or stop any plugin, read and write every file, and use the network. The
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checks protect against mistakes, not against plugins. Locks are advisory.
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- **Locks are in the core.** A plugin cannot see that another process died,
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so it cannot release that process's lock. The core can.
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- **Our own VFS, in its own crate.** It works on Linux and macOS, it makes
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`/proc` live, and plugin-served files need it later. Mounts now, overlays
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later.
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- **TCP endpoints for now.** They need no host code. VFS pipes can replace
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them later behind the same SDK API.
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- **Simple scheduling for now.** An epoch tick every 10 milliseconds keeps
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the core responsive and makes kills reliable.
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- **The agent is dumb.** It has a short prompt, a few tools, an append-only
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history that it sends in full, and no compaction. When the context is too
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large, it stops sending the oldest turns, so it never gets stuck.
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## Small choices
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- **Plain POSIX files.** Programs like `tempfile`, git, and SQLite expect
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normal files. Atomic writes use a temporary file and `rename`.
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- **Tests run under WASI.** `cargo test` on the host cannot find failures
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that occur only in WASI, for example a missing WASI function or a panic at
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start. The test runner uses the same Wasmtime and the same mounts as the
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core.
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- **The SDK is not published.** `cargo` points `sausage-plugin = "0.1"` at
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its own copy, which it also shows in `/plugins/cargo/sdk/`.
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