Closed-enum dispatcher for Lifeline target_type string → atom conversion.

Closed enum

Converts the producer-bounded target_type string values to atoms:

• "job" → :job
• "workflow" → :workflow
• "workflow_step" → :workflow_step
• "step" → :step

Current producer set

The current Lifeline repair preview and workflow handoff producers emit only "job", "workflow", and "workflow_step". The "step" value is included for forward compatibility per Phase 41 D-07.

Unknown values raise

There is intentionally no catch-all clause. An unknown target_type raises FunctionClauseError because the callers (Lifeline.repair_executed, Lifeline.host_follow_up, and LifelineLive workflow handoff) are internally trusted paths. An unknown target_type in production indicates a programming bug — a new producer was added without updating this module. The failure surfaces immediately rather than silently coercing an unknown value into an unbounded atom.