Refactor core Follow handling into stateless decisions

README.md

@@ -24,9 +24,9 @@ Approach
 --------
 
 Feder separates ActivityPub protocol logic from platform execution. The core
-should contain federation behavior such as inbox/outbox state, delivery
-decisions, and protocol-level rules. Runtimes provide platform-specific pieces
-such as networking, storage, clocks, scheduling, and execution.
+should contain deterministic protocol decisions. Runtimes provide
+platform-specific pieces such as networking, storage, clocks, scheduling, and
+execution.
 
 The first target is a Linux proof of concept for a small single-user
 ActivityPub server. Future runtimes may explore more constrained environments.

crates/feder-core/README.md

@@ -0,0 +1,17 @@
+Feder Core
+==========
+
+Pure ActivityPub decision logic for Feder.
+
+This crate does not perform HTTP, database, filesystem, clock, or random ID
+operations. A runtime provides the state and context needed for one decision,
+then applies the returned decision itself.
+
+
+Core decisions
+--------------
+
+~~~~ text
+stored state + policy + context + ActivityPub input
+    -> state changes + effects
+~~~~