Sylpheed/docker/decoder

The RE agent container

A container an autonomous Claude Code agent can be turned loose in: it builds and runs both halves of the project — Xenia Canary as the behaviour oracle and Sylpheed Reborn as the port — and carries the dynamic-RE toolkit that drives the emulator, reads its guest memory and photographs its screen.

./sylph-agent build            # build the image
./sylph-agent doctor           # prove it can do the four things it exists for
./sylph-agent shell            # poke around
./sylph-agent agent            # Claude Code, --dangerously-skip-permissions
./sylph-agent loose            # turn it loose: detached, /loop, self-paced
./sylph-agent remote           # link to chat with it from anywhere
./sylph-agent attach           # chat with it locally
./sylph-agent logs -f          # watch it
./sylph-agent stop             # stop it

On the loose

./sylph-agent loose starts Claude Code detached, with --dangerously-skip-permissions, running /loop on the task in loop-task.md — work the RE backlog one item at a time, commit to auto/* branches, never push, record withdrawn results rather than deleting them. Pass your own task as an argument, or set SYLPH_LOOP_INTERVAL=30m for a fixed cadence instead of letting it self-pace.

It runs -d without --rm, so the transcript survives the container exiting — for an unattended run that is the only record of what happened.

Talking to it

Two channels, both live while it works:

• ./sylph-agent remote prints a https://claude.ai/code/session_… link. loose starts Claude Code with --remote-control, so the session registers with your account and you can chat with it from claude.ai or your phone — which is the point of a detached run. Disable with SYLPH_REMOTE=0, rename with SYLPH_REMOTE_NAME.

  Registration takes a minute or two after launch, so remote waits for it rather than reporting "not found" to what is really "not yet".

• ./sylph-agent attach joins the container's own terminal. Type to talk to it; Ctrl-P Ctrl-Q detaches and leaves it running. Do not press Ctrl-C — that goes to the agent.

The pty is forced to 200×50 (stty_init in bin/claude-autonomous). A detached docker run -t is 80×24, and Claude Code hard-wraps to the terminal width, which truncated the Remote Control URL to …/session_01… in the one place you need to read it — and made docker logs almost unreadable besides.

It cannot push. No git credentials are mounted, deliberately: a human reviews before anything leaves the box. Review with git -C <project>/Syplheed-Reborn log --oneline main..auto/<topic>.

The four gates

Claude Code has four one-time prompts, and each one is a silent, permanent hang for an agent with nobody at the keyboard — no error, no log line, just a container that looks healthy and does nothing. All four are handled:

gate	how
theme picker	hasCompletedOnboarding + lastOnboardingVersion in ~/.claude.json
"do you trust this folder?"	projects.<path>.hasTrustDialogAccepted
Bypass Permissions disclaimer	answered in a pty by bin/claude-autonomous — it has no config key, by design
fullscreen-renderer upsell	fullscreenUpsellSeenCount, because it fires mid-session, after the pty wrapper has handed over

Config keys were read out of the shipped binary's own strings rather than guessed. The pty wrapper matches single words: Claude Code draws its UI with absolute-column escapes between words, so Yes, I accept arrives as Yes,\x1b[13GI\x1b[15Gaccept and a multi-word pattern never matches — which looks exactly like the wrapper not running at all. It stops matching once the session is live, so nothing later can be answered by accident.

The resource cap

The container gets half the machine, computed at launch so it stays half on any box:

	how
CPU	--cpus $(nproc)/2
memory	--memory = half MemTotal, --memory-swap equal to it
/dev/shm	a third of the memory cap, min 1 GiB, mounted exec
build jobs	derived inside the container from available memory, not cores

Two of those deserve a word.

No swap headroom. --memory-swap is set equal to --memory, so the container cannot swap. That is deliberate: a swapping build thrashes the whole host, which is precisely the failure the cap exists to prevent. A build that would have swapped gets OOM-killed inside the container instead, and the host stays usable.

/dev/shm is not incidental. Xenia backs the guest address space with /dev/shm/xenia_memory_*, and the whole live-memory toolkit (gmem.py, gpoke.py, mission_state.py) reads it from there. Docker's default is 64 MiB, which is far too small for a 512 MiB console — and it fails as an obscure mmap error rather than an out-of-space message.

Build parallelism is memory-bound. A full-parallel build of this tree has OOM-killed the host outright, so the entrypoint computes jobs from available memory (≈1.5 GiB per C++ TU) and exports it as SYLPH_JOBS, CARGO_BUILD_JOBS and CMAKE_BUILD_PARALLEL_LEVEL. Override with SYLPH_CPUS / SYLPH_MEM_GB.

Inside

command	what
build-canary [Release|Debug]	configure + build Canary
build-reborn [build|test|ci]	build/test Reborn, with the disc env wired up
run-canary [flags…]	launch Canary with the settings this title needs
screenshot [out.png]	grab the display
sylph-doctor	self-check
tools/re-capture/*	the RE toolkit, already on PATH

Layout: project at /work, HOME=/sylph-home/re, DISPLAY=:98 — the values tools/re-capture/*.sh already assume, so the existing toolkit runs unmodified.

Build outputs live outside the bind mount (CARGO_TARGET_DIR, XENIA_BUILD_DIR, both named Docker volumes). The host builds the same trees, and sharing target/ or build/ makes host and container reconfigure and relink everything the other just did.

Screenshots

Two layers, and the distinction matters:

• /usr/local/bin/screenshot — raw full-root PNG (ImageMagick, falling back to ffmpeg's x11grab, then xwd).
• tools/re-capture/bin/screenshot — first on PATH, wraps the above and crops to the game surface.

The crop is not cosmetic. Xenia's window is a GTK window whose menu bar pushes the 1280×720 game image down ~25 px, and every pixel oracle in the toolkit was measured against the bare game image. When that offset was unaccounted for, one run sat 300 s in front of a plainly visible MAIN MENU reporting "no main menu". The wrapper derives the offset from the window's own height rather than a per-display constant.

For finding a screen at all, prefer screen_id.py, which classifies by whole-image statistics instead of named pixels.

Vulkan

mesa-vulkan-drivers + vulkan-tools are installed, so Vulkan works with no host GPU via lavapipe (software — correct, slow). When the host has /dev/dri, the launcher passes the device through and adds the host's render and video GIDs, and the entrypoint uses the hardware ICD. Force software with SYLPH_VULKAN=sw. vulkaninfo --summary (or sylph-doctor) says which you got — and the entrypoint reports the device that actually enumerated, not the one it asked for, because "I passed /dev/dri" and "I have hardware Vulkan" are different claims.

⚠️ On an NVIDIA host, /dev/dri alone does nothing — Mesa cannot drive an NVIDIA card and the proprietary userspace lives outside the image. You need the NVIDIA Container Toolkit; the launcher detects the situation and tells you the three commands. Until then Canary runs on lavapipe, which is correct but has not been observed to reach a rendered frame in a couple of minutes — everything else (guest memory, the JIT, the live-memory toolkit) works fine on it.

Input, and why there is no virtual gamepad

run-canary passes --hid=file --pad_file=/tmp/xenia_pad.txt; drive it with tools/re-capture/pad.py. There is deliberately no /dev/uinput: input devices are not namespaced, so a virtual pad created in a container registers with the host's input stack and every scripted press leaks onto the user's desktop.

The trap that wasted a session: 360 menus poll XamInputGetKeystrokeEx, not GetState — with GetKeystroke stubbed the pad looks completely dead on a title screen while its own log shows the press arriving.

Settings that are requirements, not preferences

run-canary bakes these in; changing them will cost you an afternoon.

• --apu=sdl with SDL_AUDIODRIVER=dummy — and no --audio flag, which is not a cvar here (see below). There is no PulseAudio, so --apu=nop looks like the safe muted choice. It is not: the log fills with CreateDriver failed for index=0, the guest never gets past the intro movie, and the window stays black for 8+ minutes. SDL against a dummy device is silent and lets the title advance.
• One emulator at a time, enforced with a lockfile. Two at once perturbs both and the box.
• Stale /dev/shm/xenia_memory_* from a killed run is removed at launch — otherwise the memory readers find two candidates and pick the dead one.

Claude Code

Runs as an unprivileged agent user, because --dangerously-skip-permissions is refused under root. ./sylph-agent agent sets SYLPH_AUTONOMOUS=1 and the entrypoint adds the flag.

Auth comes from the host ~/.claude, bind-mounted read-write (token refresh needs to write). That directory also holds your memory and project state, so the container agent and you share it. Point SYLPH_CLAUDE_HOME at a separate directory to isolate it, or set ANTHROPIC_API_KEY instead.

~/.claude.json is different: mounted read-only at a staging path and copied in, so the container cannot rewrite your host config — and so a version skew between the container's Claude Code and yours cannot re-trigger onboarding.

The project is bind-mounted twice, at /work and at its own host path. The host path is what makes memory carry over: Claude Code derives its per-project state key from the working directory, so running at /work would hand the agent an empty project instead of the accumulated one. Verified — a loose run reports MEMORY=yes and reads back the same branch and backlog you see.

Host prerequisites

• A Vulkan SDK (LunarG), for building only. Canary's shader step calls spirv-opt --canonicalize-ids, which Ubuntu's packaged SPIRV-Tools (v2025.1) does not have — the build then dies ~500 objects in, and the error you see is a Python TypeError, not the real message. The launcher mounts the host's SDK read-only at its own path and sets VULKAN_SDK; that also guarantees the container produces byte-identical shaders to a host build.
• nvidia-container-toolkit, for hardware Vulkan — see below.

Things that will waste your afternoon

Each of these was hit while bringing this container up.

• An unknown xenia flag hangs; it does not error. ParseLaunchArguments calls ShowSimpleMessageBox before logging is initialised, and that SDL dialog blocks on XIfEvent forever with nobody to click it. The symptom is a 10×10 window, a completely empty log and no guest memory — which reads like a hang deep in the emulator. --audio is not a cvar in this tree despite appearing in the RE notes; --apu=sdl is the real one. If Canary appears to hang at startup, suspect a typo'd flag first.
• /dev/shm must be exec. Docker mounts it noexec, and xenia maps its JIT code cache out of a shm file. With noexec it dies at startup with "Unable to allocate code cache generated code storage / Cannot initalize processor", which reads like an address-space clash. The launcher uses --tmpfs /dev/shm:rw,exec,… rather than --shm-size.
• gdb needs root inside the container. --cap-add SYS_PTRACE is passed, but the host's kernel.yama.ptrace_scope=1 still blocks attaching to a non-descendant. Use sudo gdb -p <pid> (passwordless), or launch the target under gdb so it is a child.
• Named volumes need their mount points to exist in the image, or Docker creates them root-owned and the first write fails obscurely.

Known limitation

build-reborn ci runs the native legs only. just ci's wasm check does not build, for a pre-existing reason unrelated to any change under test: the workspace pins tokio = { features = ["full"] }, which pulls mio, which refuses to compile for wasm32-unknown-unknown.