Add Daily recent changes comparison

docs/internal/prompt-input.md

@@ -16,7 +16,7 @@ Input:
 Output:
 
 - `promptinput.Package` JSON with report metadata, briefing content, source
-  warnings, RunID, and an empty Recent Changes section.
+  warnings, RunID, and a Recent Changes section.
 
 ## Boundaries
 
@@ -30,8 +30,8 @@ Output:
 - `promptinput.Validate` rejects missing or inconsistent required fields before
   render preflight.
 - `promptinput.Save` writes JSON atomically where practical.
-- Recent Changes is present as an empty `items` list until structured comparison
-  is implemented.
+- Recent Changes is present as an `items` list. It is empty when no prior
+  comparable snapshot exists or no meaningful changes are detected.
 
 ## Failure Behavior
 
@@ -43,6 +43,7 @@ the filesystem operation and path context.
 Inspect:
 
 - `internal/promptinput/package_test.go`
+- `internal/changes/daily_test.go`
 - `internal/app/app_test.go`
 
 ## Invariants