feat(sse): sync H-104 contract

Author: loong10k

src/main/java/io/github/easy4j/hermes/transport/RequestSemantics.java

@@ -0,0 +1,33 @@
+package io.github.easy4j.hermes.transport;
+
+/**
+ * Classifies request behavior so transport recovery cannot accidentally replay side-effecting work.
+ *
+ * @since 1.0.0
+ */
+public enum RequestSemantics {
+    /** A read may be retried only by HTTP retry policy; it is not an SSE observation reattach. */
+    READ(true, false),
+    /** Creating agent work must never be replayed merely because response observation failed. */
+    AGENT_CREATE(false, false),
+    /** Side-effecting control writes require an explicit verified idempotency contract before replay. */
+    CONTROL_WRITE(false, false),
+    /** Re-observing an already existing run may reconnect without creating new work. */
+    OBSERVE(false, true);
+
+    private final boolean transportReplaySafe;
+    private final boolean observationReattachAllowed;
+
+    RequestSemantics(boolean transportReplaySafe, boolean observationReattachAllowed) {
+        this.transportReplaySafe = transportReplaySafe;
+        this.observationReattachAllowed = observationReattachAllowed;
+    }
+
+    public boolean isTransportReplaySafe() {
+        return transportReplaySafe;
+    }
+
+    public boolean isObservationReattachAllowed() {
+        return observationReattachAllowed;
+    }
+}