Execution routing: choose the execution envelope, not only the model

fak route answers one deliberately narrow question: which model plan should handle an aspect of a request? Real agent execution has at least three independent choices:

1. Harness route — which declared harness profile can execute the work (wire, repoint mechanism, and account-rotation capability).
2. Model/sub-model route — which model or ensemble handles this request, tool call, query, state operation, step, or scout.
3. Session route — start fresh, resume for continuity, fork portable state, or compact and resume when retained context is full.

fak execution-route composes those choices into one inspectable JSON envelope. It does not rename every choice “routing,” and it does not flatten them into one model string: each decision keeps its own reason and vocabulary.

Working spine

fak execution-route `
  --harnesses openai-generic,codex `
  --rotatable `
  --aspect tool_call `
  --tool write_repository `
  --session session-7 `
  --continuity `
  --context-utilization .91

The ordered harness list is operator policy. In this example openai-generic cannot rotate account homes, so the decision selects codex; the existing model router chooses the tool-call model plan; and the session decision is compact_resume because continuity is required above the default 80% threshold.

Boundaries

• Harness profiles remain declared by internal/harnessprofile and the dos.toml harnesses table. Execution routing consumes those profiles; it does not add another harness registry.
• Model policy remains the internal/modelroute manifest. The composed route embeds its full decision, including rule and reduction details for sub-model/ensemble plans.
• Session routing is declarative. It chooses a lifecycle action but does not own session storage, compaction, or migration.
• Candidate ordering and requirements are explicit inputs. The oracle does not infer quality, price, or account health that the caller did not supply.

This is the minimal end-to-end spine. Follow-on work should add measured harness capabilities/health, persistent session portability metadata, and gateway execution of the composed envelope rather than hiding those concerns in heuristic branches.