fix: cap per-entry memory length at 250 chars in context band

A 530-char program overview memory with confidence 0.96 was filling
the entire 25% project-memory budget at equal overlap score (3 tokens),
beating shorter query-relevant newly-promoted memories (confidence
0.5) on the confidence tiebreaker. The long memory legitimately
scored well, but its length starved every other memory from the band.

Fix: truncate each formatted entry to 250 chars with '...' so at
least 2-3 memories fit the ~700-char available budget. This doesn't
change ranking — the most relevant memory still goes first — but
it ensures the runner-up can also appear.

Harness fixture delta: Day 7 regression pass pending after deploy.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atocore/memory/service.py

@@ -413,8 +413,17 @@ def get_memories_for_context(
     if query_tokens is not None:
         pool = _rank_memories_for_query(pool, query_tokens)
 
+    # Per-entry cap prevents a single long memory from monopolizing
+    # the band. With 16 p06 memories competing for ~700 chars, an
+    # uncapped 530-char overview memory fills the entire budget before
+    # a query-relevant 150-char memory gets a slot. The cap ensures at
+    # least 2-3 entries fit regardless of individual memory length.
+    max_entry_chars = 250
     for mem in pool:
-        entry = f"[{mem.memory_type}] {mem.content}"
+        content = mem.content
+        if len(content) > max_entry_chars:
+            content = content[:max_entry_chars - 3].rstrip() + "..."
+        entry = f"[{mem.memory_type}] {content}"
         entry_len = len(entry) + 1
         if entry_len > available - used:
             continue