Fix: cumulative file tracking applies to both compaction and branch summarization

packages/coding-agent/docs/compaction.md

@@ -128,13 +128,12 @@ interface CompactionDetails {
 ```
 
 Hooks can store any JSON-serializable data in `details`. The default compaction tracks file operations, but custom compaction hooks can use their own structure.
-```
 
 ## Branch Summarization
 
 ### When It Triggers
 
-When you use `/tree` to navigate to a different branch, pi offers to summarize the work you're leaving. This preserves context so you can return later.
+When you use `/tree` to navigate to a different branch, pi offers to summarize the work you're leaving. This injects context from the left branch into the new branch.
 
 ### How It Works
 
@@ -163,11 +162,11 @@ After navigation with summary:
 
 ### Cumulative File Tracking
 
-Branch summaries track files cumulatively. When generating a new summary, pi extracts file operations from:
+Both compaction and branch summarization track files cumulatively. When generating a summary, pi extracts file operations from:
 - Tool calls in the messages being summarized
-- Previous branch summary `details` (if any)
+- Previous compaction or branch summary `details` (if any)
 
-This means nested summaries accumulate file tracking across the entire abandoned branch.
+This means file tracking accumulates across multiple compactions or nested branch summaries, preserving the full history of read and modified files.
 
 ### BranchSummaryEntry Structure