Run 174's Linux job failed on
ASilentlyCorruptedPackageOfTheSameSizeStillFailsAndDropsTheCache. It passed in
isolation on that same machine, and passed under full-suite load there too, so
it looked like a flake. It is not.
Measured on the runner:
same-mtime collisions: 141 / 200
fs type: zfs
Its /tmp is ZFS, whose timestamp granularity is coarse enough that a same-size
rewrite usually lands on the SAME last-write time. So the startup fast path —
size plus write time — cannot see that modification, and the test was right to
fail. LU1's commit message claimed "truncating or touching the package still
blocks launch"; on a coarse-timestamp filesystem the second half of that is
false. NTFS's 100 ns resolution is why it never showed on Windows.
Rather than relax the test until it passes, the contract is now stated as two
facts that are true everywhere instead of one that is not:
- A same-size corruption whose write time moves is caught at startup. The test
moves the timestamp explicitly instead of trusting the clock, so it asserts
the mechanism rather than the filesystem's resolution.
- A corruption preserving BOTH size and write time is NOT caught at startup and
IS caught by a forced full verification — which is exactly what the
launcher's Verify files button runs. New test, so the escape hatch is
covered rather than merely mentioned.
PreparedAssetVerificationCache now documents the limit with the measurement, so
the next reader does not have to rediscover it from a red pipeline.
Verified on Windows (11 passed) and five consecutive runs on the ZFS runner
itself (11 passed each). Full solution 14,375 passed, 0 failed.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Measured on the user's machine: %LOCALAPPDATA%\acdream\pak\acdream.pak is
29,908,271,024 bytes and SHA-256 over it takes 24.1 s at 1.16 GB/s. App
.OnFrameworkInitializationCompleted ran exactly that hash synchronously,
before constructing the window, and the digest came back identical to the one
install.json already recorded. So the launcher took roughly half a minute to
appear in order to re-confirm a fact that had not changed. A friend does not
see it only because they have no package installed yet — verification
short-circuits at "nothing installed" — so it would hit them the moment
first-run setup finished.
Startup now checks the cheap facts (size, last-write time) and skips only the
hash, and only when a previous FULL hash of that same file agreed with the
install record. Everything that should hash still does: install, update, the
crash-recovery backup path, and a new explicit "Verify files" button.
The remembered fact lives in a SIDECAR (install.verification.json), not as a
new field on the install record: LauncherInstallRecordStore reads install.json
with JsonUnmappedMemberHandling.Disallow, so a new property there would make an
older launcher build reject the record outright and demand a fresh ~28 GB bake
after a rollback. An unknown sidecar is simply ignored by builds that predate
it. The cache type never throws — it sits in front of a guarantee, so every
failure mode (missing, corrupt, unknown schema, unwritable) degrades to
"hash it again" rather than to a failed launch.
Two subtleties worth keeping:
- The write time is re-read after the hash and the entry is only written when
it is unchanged. A writer racing a multi-second hash would otherwise be
remembered under the OLD timestamp, and the next startup would trust a
digest that never covered those bytes.
- A hash that disagrees with the record invalidates the entry, so a stale
"verified" fact cannot outlive the evidence that produced it.
Tests: PreparedAssetVerificationCacheTests (10) counts hash invocations through
the store's injectable hasher and covers second-startup skip, forced full
verification, touched package, same-size silent corruption, resize, a cache
digest that disagrees with the record, three unreadable-cache shapes, and
backup recovery still hashing. Plus two LauncherWindowViewModel tests for the
Verify files command. Launcher.Core 335 passed, Launcher 57 passed.
Note for the first run after this ships: the very first startup still pays one
full hash to learn the digest for the installed file, and every startup after
that is instant.
Campaign LU slice LU1. Plan: docs/plans/2026-08-19-launcher-usability-campaign.md
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
