sim-one-alpha

D9: Use A Flue-Native Application Graph Coordinator

Status: accepted for specification; implementation pending.

Question

Should SIM-ONE Alpha add LangGraph as a second agent runtime, use a Flue workflow as the graph scheduler, or build the task coordinator around Flue’s existing agent surfaces?

Decision

Build a small application-owned TypeScript task-graph coordinator and use Flue agents, subagents, tools, skills, MCP connections, sessions, streams, and persistence as node executors.

Do not add LangGraph as a runtime dependency. Borrow its proven architectural mechanisms where they fit: typed state channels and reducers, partial updates, conditional edges, checkpointed threads, interrupts, private subgraph state, and explicit runtime context.

Do not use a Flue workflow as the TLG scheduler. Flue workflows may package bounded operations, but interrupted workflow functions do not resume from an arbitrary completed step. The SIM-ONE coordinator and Memory Helper own checkpoint and resume behavior.

Rationale

SIM-ONE Alpha is a Flue product. A second agent runtime would duplicate model, tool, subagent, persistence, event, and deployment concerns. A narrow coordinator supplies the missing graph semantics without weakening Flue ownership.

Rejected Alternatives

• Adding @langchain/langgraph and routing model work outside Flue.
• Encoding the graph entirely in prompt instructions.
• Running the whole task as one non-resumable Flue workflow.
• Keeping one hardcoded while loop per worker.

Consequences

• The coordinator must have validated definitions, a scheduler, reducer registry, checkpointer, interrupt handling, and executor adapters.
• Model execution still goes through Flue.
• Task state and recovery remain application-owned and testable without a live model.
• Flue version-matched documentation remains authoritative for agent and subagent behavior.

Affected Graph Consumers

• plan-implementation
• implement-core-contracts
• implement-agent-runtime
• implement-ingress-operations
• integrate-and-repair
• review-architecture-security
• specify-task-lifecycle-architecture
• verify-release-reconciliation-specifications

Revisit Trigger

Revisit if Flue adds a durable, resumable, step-checkpointed graph API that satisfies the same state, interrupt, context, and evidence contracts without duplicating the SIM-ONE coordinator.

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