dream: NREM does not exclude prior traces

NREM in the reframe is replay-and-consolidation of recent encoded
content. Excluding previously_retrieved sources turns NREM into
novelty-finding, which is Late REM's job. NREM should re-traverse
already-encoded content; that's what consolidation is.

The May 2 abort surfaced this — 52 sources accumulated in the
exclusion list, all of them in NREM's similarity band for the
recurring research/fabrication/teaching query. The dreamer hit
zero retrievable chunks not because the corpus was empty, but
because everything semantically aligned was excluded.

Late REM and Early REM keep the exclusion mechanism — novelty is
their job. Session-scoped exclusion (nrem_high_sources flowing
into Early REM) also preserved.

The 500/400 trim on retrieved_sources is preserved for the
remaining stages that still use it.

scripts/dream.py

@@ -473,7 +473,9 @@ def dream_pipeline():
 
     # ── Stage 1: NREM ──────────────────────────────────────────────────────
     print("\n[NREM] Retrieving...")
-    nrem_chunks = retrieve("nrem", excluded_sources=previously_retrieved | session_retrieved)
+    # NREM is replay-and-consolidation — does not exclude prior traces.
+    # Late REM and Early REM exclude prior content for novelty; NREM does not.
+    nrem_chunks = retrieve("nrem", excluded_sources=None)
     session_retrieved.update(c["source"] for c in nrem_chunks)
     # Track sources that scored above Early REM ceiling — these are the only ones Early REM should exclude
     nrem_high_sources = {c["source"] for c in nrem_chunks if c["similarity"] > 0.55}