Workflow concepts: the operator’s middle layer

fak traj concepts derives workflow concepts between fleet aggregates and individual tool calls. A concept groups sessions with similar tool sets and adjacent transitions, then exposes:

• a stable wf-… selector;
• prevalence (sessions, share) and call error rate;
• an explainable medoid signature and ranked tool label; and
• exemplar session IDs for immediate drill-down.

fak traj concepts --corpus runs.jsonl
fak traj concepts --corpus runs.jsonl --concept wf-12ab34cd
fak traj concepts --corpus runs.jsonl --json --threshold .65

The default algorithm is intentionally deterministic and inspectable: weighted Jaccard over tool-name and adjacent-transition features, followed by connected components. It is not semantic task clustering. Operators should use it to find a recurring workflow family, inspect its exemplars, and only then steer policy, routing, prompts, or tooling. The --threshold knob controls whether nearby workflows merge; raising it produces narrower concepts.

This creates the navigation path aggregate → workflow concept → exemplar session → exact call without requiring an embedding service or turning an opaque cluster into an automatic policy decision.