overthinkos/agent-forwarding

agent-forwarding -- SSH/GPG Agent Forwarding Support

Pure composition candy. This candy carries no shell config of its own; per-tool shell init lives in each tool's home candy and is inherited transitively via require:. Specifically:

• direnv hook (bash/zsh/fish) → direnv candy's shell: block.
• SSH_AUTH_SOCK redirect to KeePassXC's published agent socket → keepassxc-keyring candy's shell: block (target:local only).
• GPG_TTY=$(tty) for the pinentry-qt → libsecret → KeePassXC chain → keepassxc-keyring candy's shell: block.

Putting any of these in agent-forwarding would scatter ownership: the direnv hook isn't a KeePassXC concern, KeePassXC's socket isn't a GPG concern. The composition stays declarative; agent-forwarding pulls in gnupg + direnv + ssh-client and inherits whatever each contributes.

Candy Properties

| Property | Value | |----------|-------| | Install files | charly.yml (metalayer) | | Composition | gnupg, direnv, ssh-client |

Usage

# charly.yml
my-image:
  candy:
    base: fedora
  my-image-candy:
    candy:
      - agent-forwarding

Included in all application boxes (27 total). Not included in base images (fedora, arch) or builder images (fedora-builder, arch-builder).

How Agent Forwarding Works

Agent forwarding is a runtime feature — sockets are bind-mounted from the host into the container at charly shell / charly start (direct mode) invocation time. This layer provides the container-side binaries (gpg, ssh, direnv) needed to use the forwarded sockets.

SSH Agent Forwarding

Host: $SSH_AUTH_SOCK (any path)
  → Container: /run/host-ssh-auth.sock
  + SSH_AUTH_SOCK=/run/host-ssh-auth.sock (env var)

The container's ssh and git commands automatically use the host's SSH keys. No SSH agent runs inside the container.

Verification: charly shell <image> -c 'ssh-add -l' lists host SSH keys.

GPG Agent Forwarding

Host: S.gpg-agent (detected via gpgconf --list-dirs agent-socket)
  → Container: $HOME/.gnupg/S.gpg-agent (HOME from ai.opencharly.home label)

The container's gpg finds the forwarded socket at its standard path. Private key operations (signing, decryption) go through the host's agent. No GPG agent or keyboxd runs inside the container.

The container has its own keyring. Public keys must be imported separately:

# Export from host, import into container
gpg --export --armor KEY_ID | charly shell <image> -c 'gpg --import'

Verification: charly shell <image> -c 'gpg-connect-agent --no-autostart /bye' connects to the host agent (shows "restricted mode" — this is normal for forwarded agent sockets).

Why NOT Quadlet

Agent socket paths are session-bound — they live under $XDG_RUNTIME_DIR and change between SSH sessions, reboots, and users. Quadlet .container files are static systemd units generated once. Baking socket paths into quadlets would cause boot failures on headless servers managed via SSH.

Agent forwarding is intentionally excluded from quadlet mode. Use charly shell or charly start (direct mode) for agent access.

Settings

| Setting | Default | Env Var | Description | |---------|---------|---------|-------------| | forward_gpg_agent | true | CHARLY_FORWARD_GPG_AGENT | Forward host GPG agent socket | | forward_ssh_agent | true | CHARLY_FORWARD_SSH_AGENT | Forward host SSH agent socket |

charly settings set forward_gpg_agent false    # Disable GPG forwarding globally
charly settings set forward_ssh_agent false    # Disable SSH forwarding globally
charly settings reset forward_gpg_agent        # Re-enable (back to default: true)

Per-Box Override (charly.yml)

# ~/.config/charly/charly.yml
immich:
  candy:
    forward_gpg_agent: false    # No GPG needed for photo management
    forward_ssh_agent: false    # Security: no host SSH access
charly-fedora:
  candy:
    forward_gpg_agent: true     # Explicit (same as default)

Resolution chain: charly.yml per-box > global setting > default (true).

Where Forwarding is Applied

| Command | Volumes (mounts) | Env vars | Notes | |---------|-------------------|----------|-------| | charly shell (new container) | Yes | Yes | Full forwarding | | charly shell (exec into running) | No | Yes | Env only; sockets from start time | | charly start (direct mode) | Yes | Yes | Full forwarding | | charly cmd | No | Yes | Exec into running container | | charly config / quadlet | No | No | Intentionally excluded |

Used In Boxes

charly-arch, arch-test, comfyui, charly-fedora, fedora-test, githubrunner, immich, immich-ml, jupyter, nvidia, ollama, openclaw, openclaw-full, python-ml, selkies-desktop, selkies-labwc-nvidia, sway-browser-vnc, unsloth-studio, valkey-test

Related Candies

• /charly-infrastructure:gnupg -- GnuPG encryption tools (part of this metalayer)
• /charly-coder:direnv -- direnv environment loader (part of this metalayer)
• /charly-infrastructure:ssh-client -- OpenSSH client (part of this metalayer)
• /charly-coder:sshd -- SSH server (separate, for images that need inbound SSH)
• /charly-infrastructure:gocryptfs -- encrypted filesystem (separate credential system)

Cross-References

• /charly-build:secrets -- charly secrets gpg for managing .secrets files, GPG key management (import-key, export-key, setup, doctor), KeePassXC integration; credential store for container secrets
• /charly-core:shell -- where SSH/GPG agent forwarding happens at runtime
• /charly-core:service -- charly start direct mode forwarding
• /charly-core:charly-config -- forward_gpg_agent, forward_ssh_agent settings
• /charly-core:deploy -- per-box forwarding overrides in charly.yml

Source

charly/agent_forward.go (socket detection, mount resolution), charly/runtime_config.go (settings).

When to Use This Skill

MUST be invoked when the task involves SSH or GPG agent forwarding, the .secrets + direnv workflow inside containers, or the agent-forwarding candy. Invoke this skill BEFORE reading source code.

Related

• /charly-image:layer — candy authoring reference (charly.yml schema, plan steps, service declarations)
• /charly-check:check — declarative testing (check: block, charly check box, charly check live)