Begin milestone 3 age persistence

docs/PORTING.md

@@ -12,10 +12,20 @@ split into independently testable milestones.
 2. **Books and linking** — descriptive/linking book data components, lectern-like
    interaction, safe teleportation, and return links. **Complete.**
 3. **Ages** — dimension definitions backed by data packs, deterministic seeds,
-   lifecycle management, and persistence.
+   lifecycle management, and persistence. Make the legacy-style animated
+   linking panel the built-in destination preview. Provide optional
+   Create/Ponder and Immersive Portals integrations as alternative rotating-
+   snapshot renderers. The configurable preview modes are `AUTO`,
+   `IMMERSIVE_PORTALS`, `PONDER`, and `LEGACY`; `AUTO` prefers Immersive
+   Portals when it is installed, then Create/Ponder, and finally the built-in
+   legacy animation.
 4. **Writing system** — pages, symbols, notebooks, desks, and book assembly.
 5. **Age grammar** — translate symbol combinations into modern biome, noise,
-   dimension-type, and worldgen configuration.
+   dimension-type, and worldgen configuration. Optional integrations with
+   TerraBlender provide composable biome-region generation, while Serene
+   Seasons and Ecliptic Seasons allow Age generation to participate in their
+   respective seasonal systems. None of these integrations are required for
+   Rivencraft's core world generation.
 6. **Instability** — deterministic validation and effects with server-safe
    behavior.
 7. **Structures and polish** — libraries, crystals, portals, recipes, models,
@@ -174,20 +184,28 @@ Return Link only for that initial arrival.
 Version 0.2.8 makes Return Link creation a server setting: `ON_CREATION`
 (default), `ALWAYS`, or `DISABLED`.
 
+Version 0.2.9.0 begins Milestone 3 with a server-owned, world-persistent Age
+registry. Each Age UUID resolves exactly once to an immutable random seed,
+generation profile, generation-version marker, canonical name, and creation
+time. The temporary vanilla-dimension adapter remains in place until runtime
+Age dimensions are introduced by a later release slice.
+
 The preview code is separated behind a renderer interface and uses an isolated
 Ponder level populated from server-authoritative destination snapshots.
 
 ## Version policy
 
-Versions follow `x.y.z`:
+Versions follow `x.y.z.b`:
 
 - `x`: major release point.
 - `y`: number of completed milestones.
-- `z`: iteration within the active milestone, including bug-fix releases.
+- `z`: release slice within the active milestone.
+- `b`: bug-fix and additional-work iteration within that release slice.
 
-Starting work on a milestone increments `z`. Completing it increments `y` and
-resets `z` to zero. The first milestone-2 slice is therefore `0.1.1`, and
-milestone 2 completion will be `0.2.0`.
+Starting a release slice increments `z` and resets `b` to zero. Completing a
+milestone increments `y` and resets both `z` and `b` to zero. The first
+milestone-2 slice is therefore `0.1.1.0`; a fix on that slice is `0.1.1.1`;
+and milestone 2 completion is `0.2.0.0`.
 
 ## Milestone 1 acceptance record