diff --git a/context.lua b/context.lua
index 71058cc..095d110 100644
--- a/context.lua
+++ b/context.lua
@@ -319,11 +319,22 @@ function Context:to_messages()
     return msgs
 end
 
--- Evict the oldest pair (user + assistant) while we exceed max_turns. Returns
--- total turns evicted. Caller is responsible for rendering the §8 status line.
+-- Evict the oldest pair (user + assistant) while we exceed max_turns
+-- OR token_budget (Phase 8 pillar 5). Returns total turns evicted.
+-- Caller is responsible for rendering the §8 status line.
+--
+-- R2 guard: when system_prompt alone exceeds token_budget, the OR
+-- condition stays true even when turns are empty — would spin
+-- forever calling table.remove on a 0-length list. The `and
+-- #self.turns > 0` clause ensures we exit when there's nothing
+-- left to evict. Over-budget system_prompts (large [project]
+-- blocks, etc.) are then on the user to shrink via :tree off /
+-- :memory clear / etc.
 function Context:enforce_budget()
     local evicted = 0
-    while #self.turns > self.max_turns do
+    while (#self.turns > self.max_turns
+           or self:estimate_tokens() > self.token_budget)
+          and #self.turns > 0 do
         -- Collect evicted slice (pair: user + assistant)
         local pair = {}
         pair[#pair + 1] = self.turns[1]