fusion/docs/multi-project.md

Multi-Project

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Fusion can coordinate multiple repositories from one installation, with shared visibility and global concurrency control.

Why Use Multi-Project Mode?

Use multi-project mode when you need to:

• Operate many repos from one dashboard/CLI
• Standardize settings and workflows across projects
• Monitor global activity and system-wide execution capacity

Central Database Architecture

Multi-project metadata is stored in:

~/.fusion/fusion-central.db

Core tables:

• projects
• projectHealth
• centralActivityLog
• globalConcurrency
• nodes
• peerNodes
• settingsSyncState
• __meta

Per-project task data remains in each repo’s .fusion/fusion.db.

Peer/mesh coordination spans core + engine:

• NodeDiscovery and NodeConnection in @fusion/core handle discovery and remote node connectivity/auth.
• PeerExchangeService in @fusion/engine coordinates node-to-node sync/exchange workflows.

Registering and Managing Projects

fn project add my-app /path/to/app
fn project list
fn project show my-app
fn project set-default my-app
fn project detect
fn project remove my-app --force

--project Flag and Resolution

You can target a project explicitly:

fn task list --project my-app
fn task create "Fix oauth callback" --project my-app

Resolution order without --project:

1. explicit flag
2. default project
3. current-directory auto-detection

Project Health Tracking

Central health tracking keeps mutable project metrics, including:

• active task counts
• in-flight agent counts
• project status (initializing, active, paused, errored)

Global Concurrency Management

A singleton central record enforces system-wide limits so one project cannot monopolize all execution slots.

Isolation Modes

Projects can run with:

• in-process (default): low overhead, shared process
• child-process: stronger isolation with independent process boundary

Node Routing

Multi-project deployments use two related node fields at different layers:

1. Project runtime placement (projects.nodeId in ~/.fusion/fusion-central.db)
   • Decides where a project runtime is hosted in multi-project orchestration.
2. Task dispatch default (defaultNodeId in project settings)
   • Decides where tasks route when they do not have a per-task override.

These fields are intentionally distinct.

Runtime placement (projects.nodeId)

ProjectManager uses project registration data plus isolation mode to pick runtime type:

• isolationMode: "child-process" → always ChildProcessRuntime
• isolationMode: "in-process" + remote projects.nodeId → RemoteNodeRuntime
• isolationMode: "in-process" + local/unset/missing node assignment → InProcessRuntime

So projects.nodeId is a project host-node assignment, not a per-task override.

Task routing defaults (defaultNodeId + Task.nodeId)

Within a project runtime, effective task routing resolves as:

1. task override (Task.nodeId)
2. project default (defaultNodeId)
3. local execution

This allows each project to maintain independent routing behavior even when managed from one central registry.

Unavailable node policy in multi-project context

unavailableNodePolicy is project-scoped and can be set differently per project (block or fallback-local).

Current behavior: scheduler dispatch records effective node/source for each task, but health-based block/fallback enforcement is not yet applied in the scheduler dispatch path.

Example: different node defaults per project

• Project A (projects.nodeId assigned to remote host): runtime executes via RemoteNodeRuntime; defaultNodeId=edge-a routes unpinned tasks to edge-a.
• Project B (projects.nodeId unset): runtime stays local InProcessRuntime; defaultNodeId=edge-b still marks its task dispatch default independently.

See also:

• Settings Reference → Node Routing settings
• Task Management → Node Routing
• Architecture → Task Routing Architecture

Auto-Migration from Single-Project

On first run after upgrade:

• Existing project databases are detected
• Projects are registered into central DB automatically
• Existing single-project workflows continue working

Migration is idempotent and designed to avoid repeated re-registration.

Rollback Procedure

If central registry behavior needs to be reverted:

1. Delete ~/.fusion/fusion-central.db
2. Keep using per-project .fusion/fusion.db data
3. Fusion falls back to legacy/single-project behavior
4. Re-register projects later with fn init / fn project add

Runtime Architecture

ProjectRuntime interface

Each project runtime supports start/stop/status/metrics and access to scheduler/task store (for in-process mode).

HybridExecutor

HybridExecutor orchestrates all project runtimes and forwards project-attributed events.

IPC Protocol (child-process mode)

Host → worker commands include:

• START_RUNTIME
• STOP_RUNTIME
• GET_STATUS
• GET_METRICS
• GET_TASK_STORE
• GET_SCHEDULER
• PING

Worker → host events include:

• TASK_CREATED
• TASK_MOVED
• TASK_UPDATED
• ERROR_EVENT
• HEALTH_CHANGED

HybridExecutor Diagram

flowchart TD
    HE[HybridExecutor]
    PM[Project Manager]
    CC[CentralCore]

    HE --> PM
    HE --> CC

    PM --> A[Project A Runtime\n(in-process)]
    PM --> B[Project B Runtime\n(child-process)]
    PM --> C[Project C Runtime\n(in-process)]

    B --> IPC[IPC Worker Channel]

See also: Architecture, CLI Reference, and Missions.