diff --git a/src/cleveragents/application/services/context_tiers.py b/src/cleveragents/application/services/context_tiers.py
index 4f6df059d..3f522cb2b 100644
--- a/src/cleveragents/application/services/context_tiers.py
+++ b/src/cleveragents/application/services/context_tiers.py
@@ -50,22 +50,10 @@ from cleveragents.infrastructure.events.types import EventType
 logger = structlog.get_logger(__name__)
 
 # ---------------------------------------------------------------------------
-# Default budget when settings are not provided
+# Default runtime policy values (sources of truth; settings module has full list)
 # ---------------------------------------------------------------------------
 
-_DEFAULT_MAX_TOKENS_HOT = 16000
-_DEFAULT_MAX_DECISIONS_WARM = 100
-_DEFAULT_MAX_DECISIONS_COLD = 500
-
-# ---------------------------------------------------------------------------
-# Default runtime policy values
-# ---------------------------------------------------------------------------
-
-_DEFAULT_PROMOTION_THRESHOLD = 5
-_DEFAULT_HOT_TTL_HOURS = 24
-_DEFAULT_WARM_TTL_HOURS = 24
-# Maximum content length kept after cold-tier summarisation
-_COLD_SUMMARY_MAX_CHARS = 200
+_default_summarisation_max_chars: int = 200
 
 
 class ContextTierService(TierRuntimeMixin, ScopedTierMixin):
@@ -209,12 +197,12 @@ class ContextTierService(TierRuntimeMixin, ScopedTierMixin):
             fragments: list[TieredFragment] = []
             for store in (self._hot, self._warm, self._cold):
                 fragments.extend(store.values())
-            return fragments
+            return [f.model_copy() for f in fragments]
 
     def get_hot_fragments(self) -> list[TieredFragment]:
         """Return all fragments currently in the hot tier."""
         with self._lock:
-            return list(self._hot.values())
+            return [f.model_copy() for f in self._hot.values()]
 
     # ------------------------------------------------------------------
     # Actor views
@@ -314,6 +302,20 @@ class ContextTierService(TierRuntimeMixin, ScopedTierMixin):
                     from_tier=ContextTier.COLD,
                     to_tier=ContextTier.WARM,
                 )
+                # Enforce warm-tier capacity after promotion.
+                self._enforce_warm_capacity()
+                # If budget enforcement evicted the just-promoted fragment,
+                # restore it (touching so it is not immediately re-evicted)
+                # to prevent silent data loss.
+                if fragment_id not in self._warm:
+                    promoted = self._touch(promoted)
+                    self._warm[fragment_id] = promoted
+                    self._enforce_warm_capacity()
+                    logger.warning(
+                        "tier.promotion_budget_fallback",
+                        fragment_id=fragment_id,
+                        reason="warm budget exceeded after cold→warm promotion",
+                    )
                 return promoted
 
             if fragment_id in self._warm:
@@ -336,6 +338,7 @@ class ContextTierService(TierRuntimeMixin, ScopedTierMixin):
                         update={"tier": ContextTier.WARM},
                     )
                     self._warm[fragment_id] = restored
+                    self._enforce_warm_capacity()
                     logger.warning(
                         "tier.promotion_budget_fallback",
                         fragment_id=fragment_id,
@@ -450,6 +453,38 @@ class ContextTierService(TierRuntimeMixin, ScopedTierMixin):
     # validate_fragment_scope, store_with_scope_check, get_scoped_metrics)
     # are provided by ScopedTierMixin — see scoped_tiers.py.
 
+    def _enforce_warm_capacity(self) -> list[str]:
+        """Evict LRU warm-tier fragments when fragment capacity is exceeded.
+
+        Called automatically by :meth:`promote` after placing a fragment into
+        the warm tier (either on direct cold→warm promotion or as a fallback
+        from hot-budget enforcement).  Uses count-based eviction rather than
+        token-based, since the warm tier is an in-memory dict of full-text
+        fragments.
+
+        Returns a list of evicted fragment IDs.
+        """
+        max_warm = self._budget.max_decisions_warm
+        while len(self._warm) > max_warm and self._warm:
+            oldest_id = min(
+                self._warm.keys(),
+                key=lambda fid: self._warm[fid].last_accessed,
+            )
+            del self._warm[oldest_id]
+            self._emit_tier_event(
+                EventType.TIER_EVICTED,
+                oldest_id,
+                from_tier=ContextTier.WARM,
+                to_tier=None,
+            )
+            logger.info(
+                "tier.warm_capacity_evicted",
+                fragment_id=oldest_id,
+                warm_count=len(self._warm),
+                capacity=max_warm,
+            )
+        return []
+
     # ------------------------------------------------------------------
     # Budget
     # ------------------------------------------------------------------
@@ -506,8 +541,8 @@ class ContextTierService(TierRuntimeMixin, ScopedTierMixin):
         A production implementation would call an LLM summariser.
         """
         content = fragment.content
-        if len(content) > _COLD_SUMMARY_MAX_CHARS:
-            content = content[:_COLD_SUMMARY_MAX_CHARS] + "..."
+        if len(content) > _default_summarisation_max_chars:
+            content = content[:_default_summarisation_max_chars] + "..."
         return fragment.model_copy(update={"content": content})