diff --git a/src/scribe/mcp/server.py b/src/scribe/mcp/server.py
index 7eb1c5a..4d8bd73 100644
--- a/src/scribe/mcp/server.py
+++ b/src/scribe/mcp/server.py
@@ -131,6 +131,12 @@ _READ_ONLY_TOOLS = frozenset({
     # looked at names that had one (#3191). rule_history records a pull the way
     # the getters above do.
     "rules_due_for_verification", "rule_history",
+    # What each retrieval surface's floor and budget currently are, and what
+    # has been changed about them (#4102). Both pure reads; `tune_retrieval` is
+    # the write and is deliberately NOT here. Read access matters more than
+    # usual for these two: a session that cannot see the bar in force, or the
+    # reason it was last moved, is a session that will move it again blind.
+    "retrieval_surfaces", "retrieval_tuning_history",
 })
 
 # Every tool that WRITES, by name. Nothing reads this set at runtime — a tool
@@ -166,6 +172,9 @@ _WRITE_TOOLS = frozenset({
     "create_rule", "create_project_rule", "update_rule", "move_rule", "delete_rule",
     "create_preference", "update_preference",
     "relate_rules", "unrelate_rules", "mark_rule_verified",
+    # retrieval tuning — a write in both senses: it moves the number the arm
+    # reads, and it appends the reason to the audit trail (#4102).
+    "tune_retrieval",
     # trash
     "restore", "purge_trash",
 })