Add overlay runtime import for packed events

docs/runtime-rehost-plan.md

@@ -22,12 +22,12 @@ Implemented today:
 - snapshots, state dumps, save-slice projection, and normalized state diffing already exist in the
   CLI and fixture layers
 - checked-in runtime fixtures already cover deterministic stepping, periodic service, direct trigger
-  service, snapshot-backed inputs, save-slice-backed inputs, normalized state-fragment assertions,
-  and imported packed-event execution
+  service, snapshot-backed inputs, save-slice-backed inputs, overlay-import-backed inputs,
+  normalized state-fragment assertions, and imported packed-event execution
 
 That means the next implementation work is breadth, not bootstrap. The recommended next slice is
-wider packed-event target-family coverage plus company-collection import depth, not another
-persistence scaffold pass.
+captured-context overlay import for company-targeted packed events, not another persistence
+scaffold pass.
 
 ## Why This Boundary
 
@@ -366,30 +366,32 @@ Checked-in fixture families already include:
 
 ## Next Slice
 
-The recommended next implementation slice is wider packed-event target-family coverage on top of the
-captured save-slice workflow that now exists today.
+The recommended next implementation slice is captured-context overlay import on top of the
+save-slice and snapshot workflows that already exist today.
 
 Target behavior:
 
-- expand the executable import subset beyond the current direct-state and follow-on lanes only when
-  target resolution and field semantics are statically grounded enough to preserve headless
-  determinism
-- add the next imported object families needed to make currently parity-only packed rows executable,
-  starting with company-targeted effects
+- preserve save slices as partial state rather than pretending they reconstruct full live company
+  state
+- overlay save-derived packed-event state onto a captured runtime snapshot that already has the
+  needed company roster and other live context
+- upgrade currently blocked company-targeted packed rows when the overlaid base snapshot provides
+  every referenced company id
 - keep preserving unsupported packed rows as parity summaries instead of guessing executable meaning
 
 Public-model additions for that slice:
 
-- wider target-family summaries only where imported execution can be justified by current static
-  evidence
-- imported company/runtime context needed by the next packed-event target families
-- no shell queue/modal behavior in the runtime core
+- tracked overlay import documents that reference one base snapshot plus one save-slice document
+- runtime-side import outcome labels for packed records so blocked-missing-context and
+  blocked-unsupported cases stay explicit
+- fixture support for generic runtime-import documents, not just snapshots or save slices
 
 Fixture work for that slice:
 
-- save-slice-backed fixtures that prove real packed event records survive import and diff paths
-- regression fixtures that lock the current selective executable import boundary and the
-  unsupported/parity-only counts
+- overlay-backed fixtures that prove company-targeted packed rows execute deterministically against
+  captured company context
+- regression fixtures that lock the before/after boundary between save-slice-only imports and
+  overlay-backed imports
 - state-fragment assertions that lock both packed parity summaries and imported executable records
 
 Do not mix this slice with: