ai-workflow-skill/docs/architecture.md

Agent Coordination Architecture

Purpose

This document defines the system split between the worker-facing inbox layer and the leader-facing orch layer.

The design target is a local, file-portable agent coordination stack:

• inbox: durable communication bus
• orch: task graph and scheduling control plane
• worktree-backed task execution for code-writing workers
• optional user-facing council review workflow on top of orch
• shared SQLite database file
• leader and workers coordinated through stable CLI commands

Why Two Layers

inbox and orch solve different problems.

• inbox answers: how do agents exchange durable messages, claim work, report progress, and return results?
• orch answers: what work exists, which tasks are ready, who should get them, and what happens after a block, failure, or retry?

If inbox is reduced to pure chat storage, the scheduler must reconstruct state from message history and ownership becomes ambiguous. If inbox tries to become a full scheduler, worker concerns and leader concerns get mixed into one unstable interface.

Role Model

• user: talks only to the leader
• leader: owns the overall goal, task graph, acceptance criteria, and final integration
• worker: executes one assigned task at a time and reports through inbox
• inbox: durable thread/message/lease/artifact store
• orch: run/task/dependency/dispatch state machine built on top of inbox

Default Usage Rules

• The leader should use orch as the default control surface.
• The leader may use inbox directly for inspection or manual repair.
• Workers should use inbox only.
• Workers should not use orch.
• User-facing discussion stays with the leader.
• Code-writing workers should run in orch-assigned Git worktrees, not in the user's primary checkout.

Shared Storage Model

Both CLIs should point at the same SQLite file.

• inbox owns communication tables such as threads, messages, leases, and artifacts.
• orch owns scheduling tables such as runs, tasks, dependencies, and attempts.
• both layers append to a shared event stream for blocking waits
• orch dispatch creates or updates inbox threads.
• orch reconcile reads inbox state and updates task state.

This preserves a clean boundary while keeping deployment simple.

Worker Execution Model

For code tasks, execution should be isolated from the user's primary checkout.

• orch dispatch should create a task-attempt worktree
• the assigned worktree path should be stored in attempt metadata and inbox task payload
• the worker runtime should execute inside that worktree
• strict mode should require a committed base revision

See worktree-execution.md for the full lifecycle.

Event-Driven Waiting

The leader does not receive worker messages as an in-memory push. Workers write state into inbox, and the leader must read it back through CLI commands.

The intended solution is event-driven blocking waits, not ad hoc sleep loops.

• leaders should use orch wait
• blocked workers should use inbox wait-reply
• low-level polling may still exist internally, but it should be hidden inside the CLI

This means there is still one logical leader. The extra behavior is a blocking wait primitive, not a second leader.

Shared Event Stream

To support blocking waits cleanly, both layers should append rows to a shared events table.

Typical emitters:

• inbox: claim, progress, blocked, answer, done, fail, cancel
• orch: dispatch, answer, retry, reassign, cancel, reconcile-driven task state changes

Typical consumers:

• orch wait: watches run-scoped task events for the leader
• inbox wait-reply: watches thread-scoped reply events for a blocked worker

Every waiter should use a monotonic cursor such as event_id or message_id, so it can resume safely without reprocessing old events.

Recommended Binary Layout

The recommended v1 shape is:

• inbox binary for communication primitives
• orch binary for leader-side planning and scheduling
• one shared --db PATH

If packaging later favors a single binary, the same model can be exposed as command groups:

• agentctl inbox ...
• agentctl orch ...

Responsibility Split

inbox should own:

• directed messages
• durable threads
• worker claiming and leases
• progress, blocked, result, and failure events
• artifact references
• thread history and watch functionality
• thread-scoped waiting for replies

orch should own:

• runs
• task graph and dependencies
• ready queue calculation
• dispatch decisions
• task-attempt worktree allocation
• blocked queue review for the leader
• retries, reassignment, and cancellation
• mapping task attempts to inbox threads
• run-scoped waiting for actionable events
• reusable higher-level workflows such as council review

What Not To Mix

Do not put these into inbox:

• dependency graph logic
• automatic worker selection policy
• retry policy
• acceptance-driven task completion logic

Do not put these into orch:

• worker claiming
• low-level message append/reply primitives
• raw thread history storage

Reading Order

• inbox-cli.md: worker-facing bus and low-level message protocol
• orch-cli.md: leader-facing scheduler and task graph control plane
• worktree-execution.md: strict worktree model for code-writing task attempts
• council-review.md: user-facing three-reviewer brainstorm and voting workflow
• implementation-roadmap.md: handoff-oriented implementation order and next steps
• blog-project-example.md: concrete example using both layers

Skills

The intended skill split mirrors the CLI split.

• inbox skill: used when an agent needs to fetch work, claim a thread, send progress, ask blocked questions, reply, or return results through inbox
• orchestrator skill: used when the leader needs to create runs, decompose tasks, manage dependencies, dispatch ready work, inspect blocks, answer them, retry failures, or reassign work through orch
• council-review skill: used when the user explicitly wants a structured three-reviewer brainstorm or review with grouped and tallied recommendations