feat: add bounded npc memory retention

docs/SIMULATION_STATE_SCHEMA.md

@@ -3,7 +3,7 @@
 ## Current contract
 
 `SimulationStateRecord` is the versioned JSON boundary for the current
-simulation. The current world schema is v6 and captures:
+simulation. The current world schema is v7 and captures:
 
 - simulation seed, tick interval, tick count, clock remainder, and elapsed
   clock ticks;
@@ -18,14 +18,15 @@ simulation. The current world schema is v6 and captures:
 - directed relationship records with familiarity, trust, and the stable event
   ID that last changed trust;
 - per-NPC known-event records that reference objective event history without
-  copying it, including first-acquisition method and communicator provenance.
+  copying it, including first-acquisition method, acquisition tick, and
+  historical communicator provenance.
 
 The top-level identity is:
 
 ```json
 {
   "schema": "the_steward.simulation",
-  "schema_version": 6
+  "schema_version": 7
 }
 ```
 
@@ -57,7 +58,7 @@ its future random sequence.
 It also verifies clock remainder, resource amount/reservation/enabled
 round-tripping, presentation unload/rebind, directed relationship/cause
 round-tripping, divergent known-event state, communicated provenance, and
-rejection of unsupported schemas.
+deterministic retention boundaries, and rejection of unsupported schemas.
 
 NPCStateRecord v2 adds the resolved travel destination and whether it is
 active. Nested v1 NPC records migrate explicitly with no invented active
@@ -120,10 +121,31 @@ event.
 World schema v5 migrates actor-owned knowledge to `performed`; non-actor
 knowledge becomes `legacy` because v5 may contain either a proximity witness or
 an older implied relationship fact. Parsing never invents that missing
-provenance. Current communicated records require a distinct existing source
-who knows the same event through `performed` or `witnessed` acquisition. This
-enforces the current one-hop boundary and makes validation independent of array
-ordering.
+provenance. At runtime, communication requires a distinct source who currently
+knows the event through `performed` or `witnessed` acquisition. Persisted
+records validate that direct-method snapshot even after the source forgets.
+This enforces the current one-hop boundary and makes validation independent of
+array ordering.
+
+SimulationStateRecord v7 / KnownEventStateRecord v3 adds `acquired_tick` and a
+snapshot of the direct speaker's acquisition method. Direct facts use the
+objective event tick; newly communicated facts use the conversation tick. The
+speaker snapshot keeps historical provenance valid even if the speaker later
+forgets their own copy, while runtime communication still requires a currently
+known performed/witnessed fact and remains one-hop.
+
+World schema v6 migrates direct acquisition to the objective event tick.
+Communicated and ambiguous legacy facts receive a fresh retention lease at the
+saved simulation tick because their exact acquisition time was not previously
+stored. The v6 source record supplies the persisted direct-method snapshot.
+
+Importance is intentionally derived rather than duplicated: a fact is
+`lasting` while it is the current trust cause for one of that knower's directed
+relationships; every other fact is `recent`. Current causal facts are protected
+so relationship state remains explainable. Each NPC keeps at most three recent
+facts, and recent facts at least one simulated day old are removed at the next
+deterministic daily-sized review. The objective event stream is never pruned by
+this rule.
 
 ## Resource authority
 
@@ -161,11 +183,11 @@ This phase does not yet provide:
 
 - a save-slot menu, metadata, thumbnails, autosaves, or multiple profiles;
 - migrations from any historical world schema other than the explicitly
-  supported v1–v5 layouts;
+  supported v1–v6 layouts;
 - player inventory or player relationship records;
 - broader relationship dimensions, line-of-sight/hearing evidence,
-  acquisition timestamps, importance/retention, memory decay, or multi-hop
-  rumours;
+  continuous or personalized memory decay, reinforcement, false beliefs, or
+  multi-hop rumours;
 - persistence for the player transform or presentation-only scene state.
 
 Those features should build on this boundary rather than inventing parallel