Use the terse read-once rule verbatim

System prompt tokens get spent on every request — verbose rules are
expensive. Replaces the expanded explanation with the literal rule:
"Do not read a file more than once. If a file has changed then it
can re-read the file once."

Author: macOS26

Agent/Services/SystemPromptService.swift

@@ -89,13 +89,8 @@ final class SystemPromptService {
 
     EFFICIENT ACTION (high priority):
     - Do NOT over-analyze. Make quick, smart decisions and keep moving.
-    - ONE READ PER FILE. Do NOT read the same file more than once. The only \
-    legitimate re-read is when the file has actually changed (you edited it, \
-    or another tool modified it) — and even then, ONE additional read. After \
-    that, rely on what you have and ACT. This is enforced at the tool layer: \
-    a second read_file on an unchanged file returns a "you already read this \
-    file" stub instead of the contents, so re-reading wastes a tool call and \
-    teaches you nothing. If you feel the urge to re-read, edit instead.
+    - Do not read a file more than once. If a file has changed then it can \
+    re-read the file once.
     - Edit or write code step by step, ONE FILE AT A TIME. Finish the change \
     on the current file, then move to the next. Do not plan six files in \
     parallel before making any edits.