Timeline

The working tree -- the one place a version-control tool can lose a user's data -- had no crash simulation; only the log store did. A new faulty directory layer tears and freezes writes at a seeded crash point, and a sweep replays an update across every crash cut, reopens, and checks four invariants. Three hold: an untracked file the update must preserve is never touched, a crashed update recovers to its target through the undo journal, and the checkout record never names a check-in whose tree did not finish materializing. The fourth does not, and that is the point of the harness: the payload write lands in place rather than through the write-temp-and-rename the metadata already uses, so a crash mid-write can leave a managed file spliced from old and new bytes -- torn, but recoverable. The gate runs the three that hold; the fourth is pinned by a test asserting the splice IS produced, so it flips the day the write is made atomic. Crash-point enumeration follows TigerBeetle's storage model. check-in: 5401ce245f user: dmestas tags: trunk

Add sim/faulty_dir.zig, a decorator std.Io that cuts a run at a seeded mutating-op boundary the way a power loss does: the crashing write persists at most a torn prefix and every later mutation is a frozen no-op, so the checkout layer's own recovery moves no byte. Crash-point enumeration follows TigerBeetle's storage-fault-injection lineage, ported to the directory surface update.zig and checkout.zig write through.

Add sim/checkout_sweep.zig: it materializes a check-in, replays an A-to-B update.applyCheckin under a crash at every reachable cut, reopens, and asserts unmanaged files are preserved, the checkout record names only a complete target, and the tree recovers to the target via the undo journal. Joins the dst gate per seed at bounded cuts; the soak walks every boundary.

Finding: update.writePayload writes working files in place (createFile truncate, write, sync), not through the atomic write-temp+fsync+rename that checkout.write, the managed set, and the undo journal use. A crash mid-write can leave a file matching neither its pre- nor its post-image. The sweep pins this; a working-tree write-journal is the fix. closed check-in: 0cea021cf9 user: dmestas tags: h2-checkout-dst

Assert density was collapsing exactly where the working tree and the wire are touched: update.zig held 2 asserts across 2127 lines, serve.zig 3, transport.zig 2 -- against the hundreds in the artifact and sync cores. This pass adds 17 asserts stating invariants that already hold: the checkout-state transitions in update (managed-set, record and rollback image agreement around each applyCheckin stage), the request/response postconditions in serve (media, arity and body-ceiling), and the frame, redirect and body-cap postconditions in transport. Asserts only, no behaviour change; where a result had to be named to assert on it the error mapping is preserved exactly. All survive the deterministic simulation sweeps, which is the point of landing them before the checkout crash-recovery sweep that will hammer update. check-in: 9654d06838 user: dmestas tags: trunk