fix(search): Add LastWriteTime fingerprint to cache staleness check

In-place manifest edits (version bumps, new binaries) that keep the
same file count previously evaded staleness detection until the 24h
timer expired. Now stores the maximum LastWriteTimeUtc across all
manifests during cache build and validates it on load alongside the
existing file-count check.

Computed during the same Get-ChildItem enumeration that already
counts files — zero additional I/O.

Author: B67687

libexec/scoop-search.ps1

@@ -25,13 +25,18 @@ function init_search_cache {
         $cache = Get-Content $searchCachePath -Raw | ConvertFrom-Json -ErrorAction Stop
         $cacheAge = (Get-Date) - [datetime]::Parse($cache.timestamp)
         if ($cacheAge.TotalHours -ge 24) { return $false }
-        # Cross-check file count for staleness
-        $currentCount = 0
+        # Cross-check file count and last-write fingerprint for staleness
+        $currentCount = 0; $currentMaxWrite = [datetime]::MinValue
         Get-LocalBucket | ForEach-Object {
             $dir = Find-BucketDirectory $_
-            $currentCount += (Get-ChildItem $dir -Filter '*.json' -Recurse -ErrorAction SilentlyContinue).Count
+            $items = Get-ChildItem $dir -Filter '*.json' -Recurse -ErrorAction SilentlyContinue
+            $currentCount += $items.Count
+            foreach ($item in $items) {
+                if ($item.LastWriteTimeUtc -gt $currentMaxWrite) { $currentMaxWrite = $item.LastWriteTimeUtc }
+            }
         }
         if ($cache.fileCount -ne $currentCount) { return $false }
+        if ($cache.maxWriteUtc -ne $currentMaxWrite.ToString('o')) { return $false }
         $script:searchIndexApps = @{}
         foreach ($prop in $cache.apps.PSObject.Properties) {
             $script:searchIndexApps[$prop.Name] = @{ path = $prop.Value.path; bucket = $prop.Value.bucket }
@@ -46,9 +51,14 @@ function init_search_cache {
 
 function build_search_cache {
     $allPathsByBucket = @{}
+    $maxWriteUtc = [datetime]::MinValue
     Get-LocalBucket | ForEach-Object {
         $dir = Find-BucketDirectory $_
-        $paths = @(Get-ChildItem $dir -Filter '*.json' -Recurse -ErrorAction SilentlyContinue | ForEach-Object { $_.FullName })
+        $items = Get-ChildItem $dir -Filter '*.json' -Recurse -ErrorAction SilentlyContinue
+        $paths = @($items | ForEach-Object { $_.FullName })
+        foreach ($item in $items) {
+            if ($item.LastWriteTimeUtc -gt $maxWriteUtc) { $maxWriteUtc = $item.LastWriteTimeUtc }
+        }
         if ($paths.Count -gt 0) { $allPathsByBucket[$_] = $paths }
     }
     $totalCount = ($allPathsByBucket.Values | ForEach-Object { $_.Count } | Measure-Object -Sum).Sum
@@ -84,7 +94,7 @@ function build_search_cache {
             } catch { }
         }
     }
-    $cacheData = [PSCustomObject]@{ timestamp = (Get-Date).ToString('o'); fileCount = $totalCount; apps = [PSCustomObject]$newApps; bins = [PSCustomObject]$newBins }
+    $cacheData = [PSCustomObject]@{ timestamp = (Get-Date).ToString('o'); fileCount = $totalCount; maxWriteUtc = $maxWriteUtc.ToString('o'); apps = [PSCustomObject]$newApps; bins = [PSCustomObject]$newBins }
     $cacheData | ConvertTo-Json -Compress -Depth 4 | Set-Content $searchCachePath -Encoding UTF8
     $script:searchIndexApps = $newApps
     $script:searchIndexBins = $newBins