fix: bust PWA cache on each release build

sw.js uses __BUILDVER__ token; build.ps1 replaces it with the git
version before go build (which embeds the patched file), then restores
the template via the finally block. Installed PWA clients receive new
assets after every release.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

build.ps1

@@ -31,17 +31,33 @@ try {
 
     $out = Join-Path $OutDir "roadamp.exe"
 
-    Write-Host "Building roadamp $Version → $out" -ForegroundColor Cyan
+    Write-Host "Building roadamp $Version -> $out" -ForegroundColor Cyan
 
-    $env:GOOS   = "windows"
-    $env:GOARCH = "amd64"
-    $env:CGO_ENABLED = "0"
+    # ── Patch sw.js with build version ────────────────────────────────────────
+    # The service worker embeds a cache-bust token so installed PWA clients
+    # pick up new assets after each release. We replace __BUILDVER__ in the
+    # source file, run go build (which embeds it), then restore via git.
+    $swPath = Join-Path $PSScriptRoot 'web\static\sw.js'
+    $swOriginal = Get-Content $swPath -Raw
+    try {
+        $swPatched = $swOriginal -replace '__BUILDVER__', $Version
+        [System.IO.File]::WriteAllText($swPath, $swPatched, [System.Text.Encoding]::UTF8)
 
-    go build `
-        -trimpath `
-        -ldflags "-s -w -X main.Version=$Version" `
-        -o $out `
-        ./cmd/roadamp
+        # ── Compile ───────────────────────────────────────────────────────────
+        $env:GOOS        = "windows"
+        $env:GOARCH      = "amd64"
+        $env:CGO_ENABLED = "0"
+
+        go build `
+            -trimpath `
+            -ldflags "-s -w -X main.Version=$Version" `
+            -o $out `
+            ./cmd/roadamp
+    }
+    finally {
+        # Always restore sw.js so the template token is preserved in the repo.
+        [System.IO.File]::WriteAllText($swPath, $swOriginal, [System.Text.Encoding]::UTF8)
+    }
 
     $size = [math]::Round((Get-Item $out).Length / 1MB, 2)
     Write-Host "Done  $out  (${size} MB)" -ForegroundColor Green

web/static/sw.js

@@ -1,6 +1,9 @@
-'use strict';
+'use strict';
 
-const CACHE = 'roadamp-v1';
+// Cache name is injected by build.ps1 (token replaced with git version).
+// When the binary is built without the script, __BUILDVER__ stays literal
+// and the SW still works — it just won't auto-bust on updates.
+const CACHE = 'roadamp-__BUILDVER__';
 const SHELL = ['/', '/app.js', '/style.css', '/manifest.json', '/icon.svg'];
 
 self.addEventListener('install', e => {