Better document lowestMinVersionForCollab, and set to 1.4

packages/runtime/runtime-utils/src/compatibilityBase.ts

@@ -34,17 +34,23 @@ export const defaultMinVersionForCollab =
 	"2.0.0-defaults" as const satisfies MinimumVersionForCollab;
 
 /**
- * We don't want allow a version before the major public release of the LTS version.
- * Today we use "1.0.0", because our policy supports N/N-1 & N/N-2, which includes
- * all minor versions of N. Though LTS starts at 1.4.0, we should stay consistent
- * with our policy and allow all 1.x versions to be compatible with 2.x.
+ * The lowest supported value of {@link @fluidframework/runtime-definitions#MinimumVersionForCollab}.
+ * @remarks
+ * In each new major version, this may be bumped to indicate which version of the Fluid Framework client libraries are no longer supported for collaboration.
+ * @privateRemarks
+ * At the time this was defined (and also at the time 2.0 was released), all version of 1.x below 1.4 were no longer supported.
+ * Therefore it makes sense to not support any version below 1.4.0.
+ * Supporting 1.4 is sufficient to support all 1.x versions which were maintained at the time this constant was introduced.
+ *
+ * Future major versions will have to decide which versions of every supported major (including 1.x if still supported) they want to support:
+ * continuing to support whatever version of 1.x is the oldest supported one at the time of the major release, would make sense for 3.0.
  *
  * @privateRemarks
  * Exported for use in tests.
  *
  * @internal
  */
-export const lowestMinVersionForCollab = "1.0.0" as const satisfies MinimumVersionForCollab;
+export const lowestMinVersionForCollab = "1.4.0" as const satisfies MinimumVersionForCollab;
 
 /**
  * String in a valid semver format specifying bottom of a minor version