Host — the two remaining app-wide stall mechanisms plus main-thread pins
found by mining all nine hang reports:
- LinuxProcess.startStdinRelay wrote to a BLOCKING stdin fd on a
width-limited cooperative-pool thread, non-cancellably; wedged guests
starved the whole concurrency runtime (decode loops, watchdogs — an
app-wide freeze surviving the reconcile fix). Writes now offload to a
per-process GCD queue (vendored patch #18).
- TranscriptWriter (actor) did blocking write/fsync on the cooperative
pool; it now runs on its own DispatchSerialQueue executor.
- UserMessageBubble's truncation probe typeset entire pasted-log-sized
messages through CoreText per layout pass (100% main-thread pins in
the 07-21 hang reports); certainly-long messages now skip the probe
and render a prefix while collapsed.
- toolGroupSignature JSON-encoded every tool input in the transcript up
to 12.5x/s on the MainActor; now a structural hash. The summary pass
is trailing-throttled to 0.4s, and flatItems joins streaming chunks
once instead of re-copying the prefix per delta.
- StatusFeedFetcher.parseDate allocated three formatters per call (86%
of a pool thread in the 07-26 report); now shared statics.
Guest (vminitd) — teardown data loss and epoll registration hazards:
- IOPair no longer closes on a bare EPOLLHUP with a backpressure flush
in flight (dropped the CLI's final output line); EPOLLOUT finishes the
flush, then EOF closes loss-free. ManagedProcess.setExit closes only
stdin, letting stdout/stderr self-close on EOF, with an 8s grace pass
(patch #16).
- Epoll events carry a registration generation; the supervisor ignores
stale events for recycled fd numbers. registerFd refuses EEXIST
instead of clobbering the existing handler. TerminalIO's stdin relay
writes a dup of the terminal fd so its backpressure registration
can't collide with the stdout relay's (patch #17).
- VsockProxy flushes bytes parked toward the surviving peer on hangup,
closes the dialing socket on a failed backend connect, and
StandardIO/TerminalIO clean up partially-created pairs on setup
failure (patch #16).
Full suite: 1451+292+74+20 tests, two failures — both pre-existing
environmental (MacVM base image absent on this machine; a load-flaky
liveness test that passes 3/3 in isolation).
Co-Authored-By: Claude Fable 5 <[email protected]>
Host (dominant): AppStore.reconcileLocks polls every 3s on the MainActor
while any lock is held — effectively forever, since interrupted/errored
sessions deliberately retain locks. Each pass ran heldPathDisposition's
diverges() as three held×unmerged scans with two split-allocations per
pathsOverlap call, pinning the main thread for tens of seconds per pass
on a diverged trunk (hang-reports 2026-07-28: 100% of samples in
reconcileLocks→heldPathDisposition→pathsOverlap). That froze running
sessions' transcripts and starved the spawn path into the 60s
"produced no output" watchdog. pathsOverlap is now allocation-free
bytewise comparison with identical semantics, and divergentHeldPaths
answers all three questions from one O((held+unmerged)·depth) set.
Guest (persistence): VsockProxy threaded ONE offset pair through BOTH
relay directions; once the EAGAIN-return backpressure patch let pending
bytes persist, traffic in the other direction skewed the shared
counters, made the write leg unreachable, and spun the single
ProcessSupervisor poller thread forever — container-wide dead control
plane until VM recreation, triggered by exactly the backpressure the
host hang created. Each direction now owns its own pipe and counters
(OSFile.RelayDirection), and source EOF is only surfaced after the
pipe drains so SHUT_WR can't truncate a parked tail. Vendored patch
docs updated (#15); inert until the initfs image is rebuilt+repointed.
Co-Authored-By: Claude Fable 5 <[email protected]>
Overview doc so other agents/humans understand the shared-control-container
isolation work: the failure vectors + fixes (stdio wedge, connection leak,
control-plane HOL, OOM cross-kill, CPU/fork-bomb, per-session memory.max), the
host-vs-guest shipping surfaces, the per-exec cgroup layout + graceful fallback,
and the local vminit-image build/validate workflow + -nucleicN tag invariant.
Cross-linked from the vendored PATCHES.md.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
Adds an opt-in hard per-session memory ceiling on top of patch #9's scoped-OOM.
The exec already ships the full OCI Spec, so the limit rides
spec.linux.resources.memory.limit — no RPC/protobuf change:
- host framework: LinuxProcessConfiguration.memoryLimitInBytes; LinuxContainer.exec
stamps it onto the exec spec.
- guest: Server+GRPC.createProcess reads it back and applies it as the exec
cgroup's memory.max (new Cgroup2Manager.setMemoryMax) via createExec/ManagedProcess.
- Nucleic: ContainerServiceSettings.controlPerSessionMemoryGiB (default 0 = off),
applied only to the shared control container (ContainerManager.exec); wired
through ContainerEngine.exec.
So one session can't consume the whole shared container's memory before its own
(oom.group-scoped) OOM. Default off preserves #9's behavior. Compile-verified host
+ musl guest; rides the pending -nucleic2 image, still runtime-pending.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
Restructures the guest cgroup layout so each exec gets its OWN child cgroup
(/container/<id>/<execID>) with memory.oom.group=1, a fair cpu.weight, and a
pids.max backstop — so one control session can't OOM-kill, starve, or fork-bomb
its siblings in the shared container. The container init moves to its own leaf
so the container cgroup can delegate controllers to children (cgroup v2
no-internal-process rule). New Cgroup2Manager helpers: setOomGroup/setCpuWeight/
setPidsMax/remove.
Best-effort with graceful fallback: any failure in the per-exec setup wipes the
partial state and reverts to today's flat layout, and each exec falls back to the
container cgroup — a cgroup hiccup degrades to current behavior, never a failed
start.
COMPILE-VERIFIED via the musl cross-build; NOT yet runtime-validated. Built as
image tag -nucleic2; vminitReference stays on the validated -nucleic1 until
-nucleic2 is checked in a real container. A hard host-configured per-exec
memory.max (exec-RPC resources field) remains a follow-up.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
cctl login stores the credential in the macOS Keychain, which cctl images push
reads automatically — so pushing needs no REGISTRY_* env vars after a one-time
login. Env vars remain as a fallback.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
The swiftly toolchain used by the vminit-image CI resolves Foundation/
Virtualization but not the 'os' overlay, so 'import os' failed with
"no such module 'os'". Guarding the diagnostic logger degrades it to a
no-op under such toolchains while local (Xcode) builds keep it.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
Host-side (ships with a normal swift build):
- LinuxProcess: non-blocking stdio relay (O_NONBLOCK + nucleicDrainNonBlocking)
so a wedged stream can't head-of-line-block sibling execs' relays; atomic
stdio-or-abort start (patches #5, #6).
- Vminitd: bounded deleteProcess timeout so teardown can't hang a wedged
channel (patch #7).
- ContainerizedProcessHandle: call LinuxProcess.delete() after exit and on
force-close — fixes a per-turn leak (per-exec vsock/gRPC connection +
runConnections() task) in the long-lived shared control container. Likely
the "degrades until app restart" root cause.
- ClaudeCodeBackend: map the atomic-start abort to a recoverable AgentError so
a failed launch settles as retryable instead of locking the composer.
Guest-side (rides the custom vminitd initfs; inert until the image is built):
- ManagedProcess: offload the blocking start off the gRPC event loop (patch #8).
- Per-exec cgroups (patch #9) recorded as design only — cross-cutting.
Pipeline:
- .github/workflows/vminit-image.yml builds vminitd from the vendored source
and pushes ghcr.io/abkslm/vminit; ContainerEngine.vminitReference repointed
at the custom image.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
abkslmandClaude Fable 5