flowgraph/docs/architecture

status, last_updated

status	last_updated
reviewed	2026-05-21

@alkdev/flowgraph Architecture

Workflow graph library — DAG-based operation orchestration over graphology, with ujsx template composition and reactive execution.

Why This Exists

Flowgraph fills the gap between the operation registry (@alkdev/operations) and the call graph observability layer (@alkdev/alkhub). Operations define what can be called. The call graph records what was called. Flowgraph defines how calls are orchestrated — the structure, validation, and execution of workflows.

Without flowgraph:

• Workflows are ad-hoc — the hub coordinator manually chains registry.execute() calls with no structural validation, no type checking between steps, and no way to reuse workflow patterns.
• Call templates are hardcoded — the SDD pipeline (architect → reviewer → decomposer → coordinator → specialist) is a recurring pattern with no reusable definition.
• Abort cascading is manual — when the 3rd of 5 operations fails, the coordinator must explicitly cancel the remaining operations. Flowgraph's DAG enables structural abort propagation.
• No precondition checking — there's no way to validate that operation A's output schema is compatible with operation B's input schema before attempting the call.

Flowgraph provides three conceptual graphs, each built for a different purpose:

1. Operation Graph (Static) — built from OperationSpecs at startup; nodes are operations, edges are type-compatibility relationships. Enables cycle detection, topological ordering, and call template validation.

2. Call Graph (Dynamic) — built at runtime from call events; nodes are call invocations with status and timestamps, edges are parent-child relationships. Enables abort cascading, observability, and DAG queries.

3. Workflow Template (Declarative) — a ujsx tree that defines a reusable workflow structure. A template is a validated path through the operation graph, instantiated as a call graph at runtime.

Core Principle

The graph is the specification. The template is the authoring surface. The call graph is the execution record.

The operation graph provides static type checking and structural validation. The ujsx template provides human-readable, composable workflow definitions. The call graph captures what actually happened. Flowgraph is the bridge between all three.

Relationship to Sibling Packages

Package	Relationship
@alkdev/operations	Peer dependency. Provides OperationSpec, OperationRegistry, CallEvent, PendingRequestMap. Flowgraph consumes operation types but does not depend on a specific runtime.
@alkdev/ujsx	Direct dependency. Workflow templates are UNode trees rendered through HostConfigs. Flowgraph provides the workflow-specific host configurations (graphology DAG, reactive execution).
@alkdev/taskgraph	Pattern reference. Flowgraph follows the same graphology-wrapping pattern (FlowGraph class like TaskGraph class) but enforces DAG invariants instead of allowing cycles.
@alkdev/typebox	Direct dependency. All schemas are TypeBox Modules. Runtime validation, JSON Schema export, and Value.Check/Value.Errors.
@alkdev/pubsub	Consumer dependency, not flowgraph's dep. For event-driven call graph population. The hub coordinator uses pubsub to subscribe to call events and feed them to flowgraph — flowgraph itself works in-memory with no pubsub import.
@alkdev/cograph	Future consumer. The cognitive graph depends on flowgraph for workflow templates and execution tracking.

Current State

Flowgraph is in Phase 0/1 (exploration → architecture). No code exists yet. This architecture document set defines the WHAT and WHY before any implementation.

Architecture Documents

Document	Content
schema.md	TypeBox Module, TypeScript types, enums (CallStatus, EdgeType, NodeStatus), node/edge attribute schemas, SerializedGraph factory
operation-graph.md	Static graph from OperationSpecs, type-compatibility edges, construction paths, validation
call-graph.md	Dynamic graph from call events, node lifecycle, abort cascading, fromCallEvents construction
workflow-templates.md	ujsx components (<Operation>, <Sequential>, <Parallel>, <Conditional>, <Map>), composition rules, template→DAG hydration, serialization
host-configs.md	Graphology HostConfig (template→DAG analysis), Reactive HostConfig (template→execution engine), Instance types, removeChild
reactive-execution.md	Signal-driven status propagation, computed preconditions, abort cascade via signals, ReactiveRoot integration, lifecycle and ownership, error boundaries
analysis.md	Type-compatibility checking (input/output schema matching), compatibility depth, precondition validation, execution ordering, performance characteristics
error-handling.md	FlowgraphError hierarchy, CycleError, TypeIncompatError, ValidationError, error collection strategy
build-distribution.md	Package structure, exports map, dependencies, platform targets
flowgraph-api.md	FlowGraph class public API: constructor, type parameters, methods, delegation model, immutability guarantees
consumer-integration.md	End-to-end walkthrough from operation specs to running workflow, common patterns, module dependency map

Design Decisions

ADR	Decision
001	ujsx tree as workflow template intermediate representation
002	Enforce DAG invariants — no cycles in flowgraph
003	Storage is not flowgraph's concern — in-memory graph with export/import boundary
004	No schema version field in serialized format — consumers wrap in their own versioned envelope
005	Execution Event Log as single source of truth — call protocol events as ground truth, status/result/call-graph as projections
006	edgeType as universal required attribute on all edges; single shared graph per FlowGraph instance

Open Questions

All unresolved design questions across the architecture are tracked in open-questions.md, organized by theme with cross-references between related questions.

Consumer Context

alkhub (hub-spoke coordinator)

The hub instantiates flowgraph to:

• Build the operation graph at startup from the registry
• Validate call templates before execution
• Populate call graphs at runtime from call protocol events
• Query call graphs for observability (what's running, what failed, what's blocked)
• Persist call graph state via export() → Postgres

OpenCode Plugin (future)

An OpenCode plugin that provides workflow tools:

• workflow.validate — validate a template against the operation graph
• workflow.run — instantiate a template as a call graph and execute it
• workflow.status — query a running call graph

Cograph (future)

The cognitive graph uses flowgraph's templates and operation graph to define procedural knowledge: which operations can be composed, what the valid execution paths are, and what preconditions each step requires.

Source Structure

src/
  component/           # ujsx components for workflow definition
    operation.ts        # <Operation name="classify" />
    sequential.ts       # <Sequential>...</Sequential>
    parallel.ts         # <Parallel>...</Parallel>
    conditional.ts      # <Conditional test={fn}>...</Conditional>
    map.ts              # <Map over={array} as="item">...</Map>
    index.ts
  host/
    graphology.ts       # HostConfig: ujsx tree → graphology DAG
    reactive.ts         # HostConfig: ujsx tree → reactive execution engine
  schema/
    enums.ts           # CallStatus, NodeStatus, EdgeType, OperationType
    node.ts             # OperationNodeAttributes, CallNodeAttributes
    edge.ts             # OperationEdgeAttrs, CallEdgeAttrs, TemplateEdgeAttrs
    graph.ts            # FlowGraphSerialized (graphology export format)
    index.ts
  graph/
    construction.ts     # FlowGraph class (like TaskGraph)
    validation.ts       # Cycle detection, type-compat validation, precondition checks
    queries.ts           # topologicalOrder, ancestors, descendants, hasCycles
    mutation.ts         # updateNode, updateEdge, removeNode, removeEdge
    index.ts
  reactive/
    workflow.ts         # ReactiveRoot for workflow state
    node-status.ts      # Per-node status signals + computed preconditions + blockedByFailure
    index.ts
  analysis/
    type-compat.ts      # Schema compatibility checking between operation input/output
    workflow.ts         # Execution ordering, precondition resolution, path validation
    defaults.ts         # Default status, edge type, etc.
    index.ts
  error/
    index.ts            # FlowgraphError, CycleError, TypeIncompatError, ValidationError
  index.ts              # Barrel export

Key Design Decisions

1. ujsx as Template IR

Workflow templates are UNode trees. This gives us:

• Composability — <Sequential> and <Parallel> compose naturally as parent-child structure
• Serialization — UNode trees are JSON, trivially stored and transmitted
• Host targets — the same template renders to a graphology DAG (analysis) or a reactive execution engine (runtime) via different HostConfig implementations
• Reconciler support — incremental template updates via ujsx's reconciler (add/remove/reorder steps without full rebuild)

This is a design decision worth documenting because it's a non-obvious choice. The alternative is to define templates as plain data structures (arrays of step objects), which is simpler but loses composability, host switching, and reconciler benefits.

2. DAG-Only, No Cycles

Flowgraph enforces acyclicity. The FlowGraph class rejects cycle-creating edges at mutation time (unlike TaskGraph, which allows cycles and detects them via hasCycles()). This is because:

• Operation graphs represent type flow — a cycle means an operation's output feeds back into its own input, which is almost certainly a design error.
• Call graphs represent execution order — cycles are physically impossible (you can't have a call that is its own ancestor).
• Workflow templates represent validated paths through the operation graph — they must be DAGs by construction.

3. Storage is Decoupled

Flowgraph handles in-memory graph construction, validation, and analysis. Persistence is the caller's concern. The export()/fromJSON() boundary provides a clean serialization format (graphology native JSON) that the hub can store in Postgres. This follows the same pattern as taskgraph.

4. Template → DAG → Execution is a Pipeline, Not a Monolith

The three representations serve different phases:

• Template (ujsx tree) → authoring, composition, serialization
• DAG (graphology) → validation, type checking, topological ordering
• Execution (reactive signals) → runtime status tracking, preconditions, abort propagation

Each can exist independently. You can validate a template without executing it. You can build a call graph from events without a template. You can run a reactive workflow directly from a DAG.

Document Lifecycle

Architecture documents use YAML frontmatter with status and last_updated fields:

---
status: draft | reviewed | stable | deprecated
last_updated: YYYY-MM-DD
---

Status	Meaning	Transitions
draft	Under active development. Content may change significantly. Implementation should not start until the document reaches reviewed.	→ reviewed when all open questions are resolved and cross-cutting issues are addressed.
reviewed	Architecture is final and reviewed. Implementation may begin. API contracts are specified but not yet verified by tests. Changes require a review cycle.	→ stable when implementation is complete and API contracts are verified by tests. → draft if a fundamental redesign is needed (rare).
stable	API contracts are locked and verified by tests. Changes require a review cycle and may warrant an ADR if they affect documented decisions.	→ deprecated when superseded. → draft if a fundamental redesign is needed (rare).
deprecated	Superseded by another document. Kept for reference. Links should point to the replacement.	Removed when no longer referenced.

ADR documents use a separate Status field in their body: Proposed, Accepted, Deprecated, or Superseded. ADRs never revert from Accepted.

References

• Call protocol architecture: @alkdev/alkhub_ts/docs/architecture/call-graph.md
• Call graph storage schema: @alkdev/alkhub_ts/docs/architecture/storage/call-graph.md
• Operation types and registry: @alkdev/operations/src/types.ts, @alkdev/operations/src/registry.ts
• ujsx architecture: @alkdev/ujsx/docs/architecture/
• ujsx research on flowgraph HostConfigs: @alkdev/ujsx/docs/research/reconciler/05-flowgraph-host-configs.md
• Taskgraph architecture: @alkdev/taskgraph_ts/docs/architecture/
• SDD process: docs/sdd_process.md