Connect movement speed modifiers

Docs/MovementAndTimeScaleBaseline.md

@@ -115,3 +115,49 @@ Later movement work should separate:
 - stamina cost and recovery;
 - injury/load/terrain modifiers;
 - skill, age, care history, and condition effects.
+
+## Movement Modifier Implementation
+
+MVP movement speed is now calculated as:
+
+`base speed * movement modifier`
+
+The base speed is either the walking baseline or the short sprint baseline.
+The movement modifier is clamped so early gameplay remains controllable while
+still allowing meaningful penalties.
+
+Live inputs:
+
+- age placeholder, replicated on the character;
+- physical condition placeholder, replicated on the character;
+- strength placeholder, replicated on the character;
+- endurance placeholder, replicated on the character;
+- hunger from the survival component;
+- thirst from the survival component;
+- injury severity from the survival component;
+- carried item weight from the inventory component;
+- terrain movement multiplier hook, replicated on the character.
+
+Current rules:
+
+- dead characters have a `0.0` survival movement multiplier;
+- hunger below `50` gradually reduces movement to `0.85`;
+- thirst below `50` gradually reduces movement to `0.75`;
+- injury can reduce movement down to `0.5` at maximum injury severity;
+- carried weight has no penalty under comfortable carry weight;
+- carried weight scales down to `0.65` as it approaches heavy carry weight;
+- carried weight at or above heavy carry weight uses a `0.45` carry multiplier;
+- strength increases the effective comfort and heavy carry thresholds;
+- endurance improves the movement multiplier and reduces sprint stamina cost;
+- terrain can slow or slightly boost movement through a replicated multiplier.
+
+Reserved systems:
+
+- age is currently an editable/replicated placeholder until the lifecycle system
+  owns it;
+- physical condition is currently an editable/replicated placeholder until care,
+  illness, sleep, and long-term health systems own it;
+- strength and endurance are currently editable/replicated placeholders until
+  character progression owns them;
+- terrain is currently a hook for later surface, slope, mud, water, road, and
+  biome systems.