Add a new feature roadmap and implementation plan for D&D prompt ordering to improve LLM provider caching

docs/roadmap/future.md

@@ -60,6 +60,30 @@ safety checks, and deterministic application of accepted changes.
 - Add media-type validators when non-JSON artifact representations are
   introduced.
 
+## LLM Runtime Evolution
+
+### Native Session Propagation
+
+- Once upstream Scriptorium exposes a session identifier on its run request,
+  propagate the existing `StructuredCompletionRequest.SessionID` through the
+  Scriptorium adapter's native session field.
+- Preserve the current `--session-id` invocation contract and its run-wide
+  propagation to every prompt-facing module and validator. Do not introduce a
+  second session configuration surface.
+- Retain session identity in checkpoint provenance so runs with different
+  sessions cannot reuse one another's LLM-derived checkpoints.
+- Define the upstream compatibility and prompt-variable transition explicitly:
+  native provider session behavior must not silently remove a `session_id`
+  prompt variable while maintained prompts still consume it.
+- Add adapter and assembled-run coverage for exact forwarding, trimming,
+  concurrent-run isolation, and unsupported-provider behavior once the
+  upstream contract is available.
+
+This work is blocked on native session support in the upstream Scriptorium
+package. Notarius already carries a run-scoped session ID through its CLI,
+pipeline requests, checkpoint identity, and prompt variables; the missing
+capability is native propagation across the LLM adapter boundary.
+
 ## Further Reference Evolution
 
 - Make prior-run artifacts easier to bind as references without changing the