ADR-330: Adaptive Pheromone Swarm Consensus

Status: Accepted and implemented Date: 2026-07-29 Issue: #2832 Supersedes: the research-only contract in draft PR #2833 Related: ADR-320, ADR-322, ADR-324, ADR-329

Decision

Ruflo adds the opt-in pheromone-adaptive swarm topology. It learns a bounded fitness signal after task outcomes and controls whether an agent is eligible for future Ruflo-managed dispatch. It does not terminate agents or expand any agent capability.

The public initialization contract is:

ruflo swarm init \
  --topology pheromone-adaptive \
  --max-agents 8

The topology starts in dry-run calibration mode. Applying suspensions requires the explicit --apsc-live flag:

ruflo swarm init \
  --topology pheromone-adaptive \
  --max-agents 8 \
  --apsc-live

This corrects the draft proposal's --maxAgents example. Kebab-case is the public CLI contract; camelCase remains the internal parsed/MCP representation.

Signal

Each observation is normalized before it reaches the coordinator:

raw = α × taskSuccess
    + β × (1 - normalizedLatency)
    + γ × consensusAlignment

Defaults are α=0.5, β=0.2, and γ=0.3. Inputs and weights are finite and bounded to [0,1]; weights are normalized to sum to one.

The raw terms are observations, not interchangeable physical measurements. Ruflo therefore does not compare raw scores directly across roles. It centers each observation on the role's EMA baseline:

roleNormalized = clamp(0.5 + raw - roleBaseline, 0, 1)
agentEMA        = decay × priorEMA + (1-decay) × roleNormalized

This prevents a coordinator or specialist with fewer discrete completions from being compared as though it were a task-producing coder.

Safety invariants

The optimizer cannot trade away these invariants:

1. coordinator, queen, security-architect, and security-auditor are protected by default.
2. An agent receives at least minSamples=3 observations before pruning.
3. At least minActiveAgents=3 remain eligible.
4. At most maxSuspendFraction=0.25 of active agents may be suspended in one observation round.
5. Suspension affects Ruflo scheduling eligibility only. It does not kill the process, discard context, revoke memory, or mutate permissions.
6. Dry-run is the default. Live mode is an explicit operator decision.
7. A suspended agent is reactivated after recovery or by deterministic bounded exploration.
8. Invalid or missing state fails open for dispatch: existing topologies and previous installations continue to execute.
9. Cross-process outcome updates use a workspace-scoped lock and atomic state replacement; concurrent hooks cannot silently overwrite one another.

Runtime integration

The implementation lives on the actual Ruflo paths:

• cli/src/services/pheromone-adaptive.ts: pure scoring and safety state
• cli/src/mcp-tools/swarm-tools.ts: persistence and MCP operations
• cli/src/mcp-tools/hooks-tools.ts: automatic post-task signal
• cli/src/mcp-tools/agent-tools.ts: scheduling eligibility gate
• cli/src/commands/swarm.ts: topology and inspection CLI
• shared/src/core/interfaces/coordinator.interface.ts: topology contract

The earlier draft named paths that do not exist in the repository. The implemented surface attaches to the persistent swarm store used by swarm_init and the tracked-agent execution path used by agent_execute.

MCP operations:

• swarm_pheromone_update
• swarm_pheromone_status

Human inspection:

ruflo swarm pheromone
ruflo agent metrics --format json

Manual observation:

ruflo swarm pheromone \
  --agent-id coder-1 \
  --role coder \
  --task-success 1 \
  --normalized-latency 0.2 \
  --consensus-alignment 0.9

hooks_post-task emits the same observation automatically when a pheromone-adaptive swarm is active.

Evaluation and claims

The Dream-cycle report cited a 50% agent reduction and 11.6% fitness increase from a different workload. Those numbers are upstream hypotheses, not Ruflo results.

Ruflo's benchmark reports:

• update latency distribution;
• active-agent reduction on a declared synthetic workload;
• quorum preservation;
• protected-role preservation;
• mean admitted-agent score before and after;
• exact configuration and seed.

Release text may claim only measured Ruflo results produced by that benchmark.

Backward compatibility

• All existing topology strings retain their behavior.
• Default topology remains hierarchical.
• adaptive is unchanged.
• Old swarm-state documents without apscState remain readable.
• Non-APSC agent_execute calls have no additional denial path.
• Dry-run APSC never denies dispatch.

Acceptance tests

1. The new topology initializes and persists through the existing swarm store.
2. APSC dry-run records decisions without changing eligibility.
3. Live APSC never crosses its active-agent floor.
4. Protected roles are never suspended.
5. A recovered agent can be reactivated.
6. Invalid score/config values are rejected.
7. hooks_post-task feeds active APSC state.
8. agent_execute refuses an agent only when live APSC marks that exact ID suspended.
9. Existing topology schemas and presets still parse.
10. Benchmark output distinguishes measured results from upstream claims.
11. Twenty concurrent outcome writers produce twenty persisted rounds and no residual lock file.
12. agent metrics exposes the per-agent EMA pheromone score, role, sample count, and current scheduling eligibility.