fix(plan): perbaiki fixture test shaping agar benar-benar men-drop pesan

Ditemukan implementer Task 5: fixture pesan pendek (~8 token nyata
lewat tiktoken untuk 20 pesan = ~160 token) tidak pernah melebihi
target 700 token (70% dari max_wire_tokens=1000), jadi force=true pun
tidak pernah men-drop satu pesan pun -- test placeholder-summary dan
keeps-most-recent lulus secara vakum tanpa benar-benar menguji jalur
drop. Diverifikasi ulang dengan context::tokens::count_tokens nyata:
fixture baru (20 pesan ~49 token = ~980 token total) melebihi target
700 dengan nyaman.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/superpowers/plans/2026-07-16-context-compaction-overhaul.md

@@ -1057,11 +1057,29 @@ mod tests {
         assert_eq!(result.len(), messages.len());
     }
 
+    /// Build a message whose real BPE token count is large enough that 20
+    /// of them (~49 tokens each, ~980 total — verified empirically with
+    /// `context::tokens::count_tokens`) comfortably exceed
+    /// `shape_messages`'s 70%-of-1000 = 700 token target, guaranteeing
+    /// several get dropped. A short fixture like `format!("message {i}")`
+    /// (~8 tokens each, ~160 total for 20) stays entirely under budget
+    /// with real BPE counting and would make these tests pass vacuously
+    /// (nothing ever gets dropped, so "must survive shaping" and "falls
+    /// back to placeholder" hold trivially without exercising the actual
+    /// drop logic) — this was a real bug caught during Task 5's first
+    /// implementation attempt.
+    fn padded_message(i: usize) -> String {
+        format!(
+            "message number {i} with some padding text {}",
+            "additional padding content to increase token count substantially ".repeat(5),
+        )
+    }
+
     #[test]
     fn shape_messages_always_preserves_the_first_system_message() {
         let mut messages = vec![ChatMessage::system("system prompt")];
         for i in 0..20 {
-            messages.push(ChatMessage::user(format!("message {i}")));
+            messages.push(ChatMessage::user(padded_message(i)));
         }
         let result = shape_messages(&messages, 100_000, 1000, true, None);
         assert_eq!(result[0].content.as_deref(), Some("system prompt"));
@@ -1071,7 +1089,7 @@ mod tests {
     fn shape_messages_without_a_client_falls_back_to_placeholder_summary() {
         let mut messages = vec![ChatMessage::system("system prompt")];
         for i in 0..20 {
-            messages.push(ChatMessage::user(format!("message number {i} with some padding text")));
+            messages.push(ChatMessage::user(padded_message(i)));
         }
         let result = shape_messages(&messages, 100_000, 1000, true, None);
         let has_placeholder = result.iter().any(|m| {
@@ -1084,7 +1102,7 @@ mod tests {
     fn shape_messages_keeps_most_recent_messages_over_older_ones() {
         let mut messages = vec![ChatMessage::system("system prompt")];
         for i in 0..20 {
-            messages.push(ChatMessage::user(format!("message number {i} with some padding text")));
+            messages.push(ChatMessage::user(padded_message(i)));
         }
         let result = shape_messages(&messages, 100_000, 1000, true, None);
         let last_content = messages.last().unwrap().content.clone();