fix(build): record the baked stamp clock, not the live one (#123308)

write-build-stamp.mjs rewrites the stamp's `builtAt` clock on every build, so the
whole-file hash moved under a receipt that had just recorded it. Two builds
overlapping on one tree failed with "Build inputs changed during compilation" for
a difference the build machinery itself made, and the caller turned that into
SystemExit(1).

Hash the stamp's provenance identity instead, key-sorted so a cosmetic
re-serialisation is not a change. The clock is excluded from that comparison but
recorded as `stampClock` — the value the bake actually embedded, captured from
the same read that produces __HERMES_INSTALL_STAMP__ — because packaging copies
the live stamp into the bundle after the receipt is written. Re-reading the stamp
at record time would certify a clock the output never contained, and
productCurrent would then report a bundle current whose packaged clock disagrees
with its baked main, which is exactly what detectBundleSwap must never do.

recordProduct still compares the prepared inputs, so a clock-only restamp cannot
throw. productCurrent additionally requires the recorded clock to match, so a
restamp between bake and packaging is a rebuild rather than a silent divergence.
A receipt predating the field compares by hash alone until the next build
rewrites it; the release packaging path never consults productCurrent.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/build/README.md

@@ -128,10 +128,17 @@ It records product/host identity, content hashes of workspace/shared sources and
 build inputs, and the exact supplied icon directory, desktop install stamp, and
 native-dependency tree. The desktop stamp is hashed as its provenance identity
 rather than its raw bytes: `write-build-stamp.mjs` rewrites the `builtAt` clock on
-every build, so hashing it byte-for-byte let the build's own first step invalidate
-the receipt it was about to write (#123308). Inputs are checked again before
-publication: a concurrent input change fails the build and preserves the previous
-output. Output validation
+every build, so hashing it byte-for-byte let a second build racing this one kill
+it with "inputs changed" for a difference the build machinery itself made
+(#123308). The clock is not dropped, only excluded from that comparison: the
+receipt records it as `stampClock`, the value the bake actually embedded, because
+packaging copies the live stamp file into the bundle *after* the receipt is
+written. A product whose packaged clock disagrees with the clock baked into its
+main process must not be reported current — `detectBundleSwap` would otherwise
+offer a relaunch for a bundle that was never replaced. A receipt predating the
+field is compared by hash alone until the next build rewrites it. Inputs are
+checked again before publication: a concurrent provenance change fails the build
+and preserves the previous output. Output validation
 checks renderer/main/preload/public bytes and the native file inventory; native
 bytes may change through signing after compilation. Native ABI verification remains
 with the native provider and desktop compiler.

scripts/build/desktop.mjs

@@ -59,11 +59,15 @@ export async function buildDesktop({ source, out, icons, stamp, nativeDeps, type
       cacheDir: join(scratch, 'vite-cache'),
       build: { outDir: product, emptyOutDir: true },
     })
-    await bundleElectronMain({ source, out: product, stamp })
+    // The receipt must carry the clock this output BAKED, not whatever the live
+    // stamp says by now: electron-builder copies that live file into the bundle
+    // after the receipt is written, and productCurrent must be able to tell that
+    // the two disagree (#123308).
+    const { stampClock } = await bundleElectronMain({ source, out: product, stamp })
     copyNativeTree({ nativeDeps, out: join(product, 'node_modules') })
     const result = checkDistBuilt(product)
     if (!result.ok) throw new Error(result.error)
-    recordProduct({ source, product: 'desktop', out: product, inputs })
+    recordProduct({ source, product: 'desktop', out: product, inputs, stampClock })
   }, { source })
   return { out }
 }

scripts/build/freshness.mjs

@@ -65,25 +65,55 @@ function outputHash(out) {
 }
 
 // The desktop install stamp is a real prepared input — buildDesktop bakes its bytes
-// into electron-main.mjs — but write-build-stamp.mjs rewrites `builtAt` on every build
-// (#123308). Hashing the whole file made the build's own first step invalidate the
-// receipt it was about to write, so a second build racing the first killed it on
-// "inputs changed". Hash the identity the output actually depends on instead:
-// the baked bytes change only when provenance does, never when the clock moves.
+// into electron-main.mjs — but write-build-stamp.mjs rewrites its `builtAt` clock on
+// every build (#123308). Hashing the whole file let a second build racing this one
+// kill it with "inputs changed" for a difference the build machinery itself made.
+// Hash the stamp's provenance identity instead: commit/payload/tag must still
+// invalidate, and only the clock is ignored.
+//
+// The clock is NOT dropped, only excluded from this comparison. It is recorded
+// separately in the receipt as `stampClock` — the value the bake actually used —
+// because the output really does embed it: outputHash covers dist/ at build time,
+// but electron-builder's extraResources copies the live stamp file into the bundle
+// afterwards (electron-builder.config.cjs), so a restamp landing between the two
+// would ship a bundle whose Resources/install-stamp.json disagrees with the baked
+// main, and detectBundleSwap (bundle-swap.ts) would report a swap for a bundle
+// that was never replaced. The path differs per packager (the desktop workspace
+// stamp, the release bundle's own stamp, a Nix store path); the race does not.
 const stampClockFields = new Set(['builtAt'])
 
-// An unreadable/non-JSON stamp is not an identity loss: its bytes still feed the hash,
-// so the file's content keeps deciding freshness and only the clock is ignored.
+// Key order is not part of provenance: write-build-stamp emits one fixed literal
+// order today, but a cosmetic re-serialisation must not force a rebuild.
+function stampIdentity(identity) {
+  return Object.fromEntries(Object.entries(identity)
+    .filter(([key]) => !stampClockFields.has(key))
+    .sort(([a], [b]) => (a < b ? -1 : a > b ? 1 : 0)))
+}
+
+// Missing and non-JSON stamps fall back to the whole-file tree hash rather than
+// failing: a missing input must keep reading as one distinct hash, never as a
+// throw, so a build that has not stamped yet stays "not current" instead of
+// aborting. Only a parsable stamp object can have its clock removed.
 function stampContentHash(path) {
-  let raw = readFileSync(path)
-  let identity
+  const parsed = readStamp(path)
+  return parsed ? createHash('sha256').update(JSON.stringify(stampIdentity(parsed))).digest('hex')
+    : treeHash(resolve(path), ['.'], () => false)
+}
+
+function readStamp(path) {
+  let identity = null
   try {
-    identity = JSON.parse(raw)
-  } catch { return treeHash(resolve(path), ['.'], () => false) }
-  if (!identity || typeof identity !== 'object' || Array.isArray(identity)) return treeHash(resolve(path), ['.'], () => false)
-  return createHash('sha256').update(JSON.stringify(
-    Object.fromEntries(Object.entries(identity).filter(([key]) => !stampClockFields.has(key))),
-  )).digest('hex')
+    identity = JSON.parse(readFileSync(path))
+  } catch { return null }
+  return identity && typeof identity === 'object' && !Array.isArray(identity) ? identity : null
+}
+
+/** The clock the output bakes, or null when the stamp is absent/unparsable. */
+function stampClock(prepared = {}) {
+  const path = prepared.stamp
+  if (!path) return null
+  const identity = readStamp(resolve(path))
+  return identity ? (identity.builtAt ?? null) : null
 }
 
 export function buildInputs(source, product, prepared = {}) {
@@ -99,23 +129,40 @@ function preparedPaths(inputs) {
   return Object.fromEntries(inputs.prepared.map(({ name, path }) => [name, path]))
 }
 
-export function recordProduct({ source, product, out, inputs }) {
+// The clock the compiler BAKED, not the clock on disk now. desktop.mjs must pass
+// the clock it read at bundleElectronMain: re-reading the stamp here would record
+// a restamp that landed in between as the baked value, and productCurrent would
+// then certify a product whose packaged clock disagrees with electron-main.mjs.
+// Undefined (tui/web, which have no stamp) is dropped from the receipt, which is
+// exactly the "predates this" shape productCurrent already tolerates.
+export function recordProduct({ source, product, out, inputs, stampClock }) {
   if (JSON.stringify(buildInputs(source, product, preparedPaths(inputs))) !== JSON.stringify(inputs)) {
     throw new Error('Build inputs changed during compilation; retry the build')
   }
   writeFileSync(join(out, receiptName), JSON.stringify({
     schema: 1, product, platform: process.platform, arch: process.arch, node: process.versions.node,
-    inputs, outputHash: outputHash(out),
+    inputs, stampClock, outputHash: outputHash(out),
   }) + '\n')
 }
 
 export function productCurrent({ source, product, out, prepared }) {
   try {
     const saved = JSON.parse(readFileSync(join(out, receiptName), 'utf8'))
+    const paths = prepared ?? preparedPaths(saved.inputs)
     return saved.schema === 1 && saved.product === product
       && saved.platform === process.platform && saved.arch === process.arch
       && saved.node === process.versions.node
-      && JSON.stringify(saved.inputs) === JSON.stringify(buildInputs(source, product, prepared ?? preparedPaths(saved.inputs)))
+      // The pre-build gate, unlike recordProduct, must also see the clock. A restamp
+      // that lands after the build (a racing write-build-stamp, or a second builder
+      // that reached extraResources first) leaves dist baking one builtAt while the
+      // live stamp says another, and packaging would then ship a bundle that
+      // detectBundleSwap reports as replaced. A receipt with no recorded clock
+      // predates this and stays comparable by hash alone. That branch is not a
+      // packaging hole: the release path (scripts/bundles/desktop.py) never consults
+      // this gate, it always stamps and compiles, and the source launchers that do
+      // consult it reuse the dist already on disk rather than packaging a new bundle.
+      && (saved.stampClock === undefined || saved.stampClock === stampClock(paths))
+      && JSON.stringify(saved.inputs) === JSON.stringify(buildInputs(source, product, paths))
       && saved.outputHash === outputHash(out)
   } catch { return false }
 }