# Architecture

## Recommended shape

Lumbridge should be two cooperating Rust processes:

```text
native desktop UI
      | local authenticated IPC
Lumbridge session runtime
      |-- local PTYs and process trees
      |-- SSH/Tailscale transport to remote Lumbridge runtimes
      |-- ACP clients and adapters
      |-- repositories and worktrees
      |-- usage/event ledger
      `-- secret-store handles
```

Separating the UI from the session runtime lets terminals survive renderer
restarts, permits a future headless/SSH mode, and gives persistence one owner.
The first development build may run both in one process, but boundaries and IPC
messages should be real from the beginning.

## Planned crates

- `lumbridge-core`: IDs, commands, events, errors, capability and usage types.
- `lumbridge-runtime`: session ownership, supervision, recovery, IPC server.
- `lumbridge-pty`: portable PTY and process-tree adapters.
- `lumbridge-terminal`: VT parsing, scrollback, selection, search, render model.
- `lumbridge-acp`: ACP client, capability negotiation, transcript normalization.
- `lumbridge-harness`: manifests, launch profiles, hooks, PTY fallback adapters.
- `lumbridge-provider`: BYOK providers and provider-neutral usage records.
- `lumbridge-storage`: SQLite migrations, event log, snapshots, retention.
- `lumbridge-remote`: OpenSSH/Tailscale command construction, framed stdio,
  handshake, reconnect, heartbeat, and remote-runtime discovery.
- `lumbridge-secrets`: Keychain/libsecret adapters and redaction.
- `lumbridge-git`: repositories, worktrees, diffs, status, conflict state.
- `lumbridge-buzz`: credential-free Buzz event/broker preparation and pane-share
  safety gates; platform adapters own signing and transport.
- `lumbridge-ui`: native desktop state and rendering.
- `lumbridge`: installable application entry point.

The scaffold currently contains `lumbridge-core`, `lumbridge-storage`,
`lumbridge-buzz`, and the entry point. Larger runtime crates are added after
their architecture spikes pass.

## Terminal path

The runtime owns PTYs, child process groups, resize signals, input ordering, and
raw output. The terminal engine turns output into immutable render snapshots and
bounded deltas for the UI. Scrollback is chunked and persisted separately from
the live screen to prevent large agent transcripts from blocking input.

We should evaluate, not blindly copy, WezTerm, Zellij, RMUX, tmux, and cmux. The
first spike must compare a reusable terminal crate with a small first-party layer.
Correctness cases include alternate screen, bracketed paste, OSC 8 links, Kitty
keyboard/graphics negotiation, Unicode width, IME, mouse modes, shell integration,
and simultaneous automation plus human input.

## UI decision gate

Do not lock the project to a webview or to Zed's private implementation details
before a measured spike. Compare:

1. GPUI for a Zed-like native model and excellent text-heavy interaction.
2. Floem for an independent native Rust model with existing editor primitives.

The winner must render six busy panes smoothly, keep input latency low, support
IME/accessibility, package on macOS and both Linux targets, and avoid a license
or upstream-stability trap.

## Local-first and remote session path

SQLite is device-local. It stores workspace metadata, pane layouts, event and
usage history, remote routing profiles, and small snapshots. It never stores SSH
private keys, Tailscale credentials, provider API keys, or subscription tokens.
Secrets remain in the OS credential store or in the user's existing SSH agent.

A remote pane is not a local PTY wrapped around a long-lived `ssh` process. Its
durable owner is a per-user `lumbridge-runtime` on the destination:

```text
MacBook Lumbridge UI/runtime
       |
       | ssh host lumbridge remote connect --stdio
       | or: tailscale ssh host lumbridge remote connect --stdio
       v
remote per-user Lumbridge runtime -- Unix socket -- PTYs, agents, worktrees
       |
       `-- remote SQLite + chunked scrollback on that machine
```

The SSH child carries a versioned framed protocol over stdio. Normal OpenSSH
remains the default because it honors the user's config, agent, host keys,
ProxyJump, and Tailscale addresses. `tailscale ssh` is an explicit transport for
users who want Tailscale's SSH proxy and host-key path. Lumbridge does not
configure a tailnet, weaken ACLs, copy SSH keys, or require a listening TCP port.

The remote runtime assigns a stable session ID before acknowledging a launch.
On network loss the local pane becomes disconnected, the remote PTY continues,
and reconnect resumes from the last acknowledged output sequence. A second
authorized Lumbridge installation can attach to the same remote session after
the remote runtime arbitrates input ownership. Collaborative simultaneous input
is not part of the first release.

## Harness integration

Each harness is described by a versioned manifest: executable discovery, launch
arguments, environment allowlist, resume semantics, status/usage probes, ACP
command when available, and hook installation rules.

ACP is preferred because it provides structured prompts, plans, tool calls,
permissions, content blocks, and session lifecycle. A supervised PTY is always
available because terminal fidelity and arbitrary CLI compatibility are product
requirements. Harness-specific adapters translate both paths into the same event
model without pretending a PTY has capabilities it cannot prove.

## Usage model

Usage is an append-only observation stream, not a mutable percentage field.
Observations include account profile, provider, harness, model, units, time
window, reset time, provenance, confidence, and source timestamp. Projections are
derived views that can be recomputed as forecasting improves.

Subscription balance is provider-specific and sometimes unavailable. BYOK calls
usually expose token counts but cost still depends on cached tokens, reasoning,
tool calls, and current pricing. Adapters normalize facts without erasing their
source or uncertainty.

## Buzz collaboration

Buzz channel messages, replies, agents, and attachments use the upstream Rust
SDK's signed Nostr semantics. SQLite stores a public identity and opaque
credential-store handle, never the private identity key. Pane images cross the
network only after local capture, redaction preview, explicit destination, and
confirmation. See `BUZZ_INTEGRATION.md` for the contract and test plan.

## Persistence

SQLite in WAL mode stores metadata, commands/events, normalized usage, and small
snapshots. Large scrollback chunks and binary attachments use content-addressed
files. A write-ahead event is committed before an external mutation is reported
as accepted. Startup replays incomplete operations and reconciles live children.

Default data roots are `~/Library/Application Support/ai.karti.lumbridge/` on
macOS and `${XDG_DATA_HOME:-~/.local/share}/lumbridge/` on Linux. Backups and
exports are explicit; Lumbridge does not synchronize the database through a
hidden hosted account.

## Security

- macOS secrets: Keychain; Linux secrets: Secret Service/libsecret, with an
  explicit encrypted-file fallback only if the user enables it.
- Never pass keys in process arguments. Prefer inherited file descriptors or a
  minimal child environment when a harness requires environment variables.
- IPC is local, authenticated, permission-restricted, and version-negotiated.
- Transcript and crash-report redaction happens before persistence or export.
- Repository trust, harness approval mode, and sandbox mode are visible per pane.
- Remote control and plugins are out of scope until a capability/permission model
  exists.

## Platform adapters

Shared contracts cover PTY, process tree, notifications, secret store, paths,
autostart, updater, and packaging. macOS uses `forkpty`/process groups and native
Keychain. Ubuntu and Omarchy use Unix PTYs, cgroups/systemd scopes when available,
and Secret Service. Omarchy is treated as Arch Linux, not as a separate kernel.