GeezerVison

Signing flow. One-time setup, what happens when the agent connects, and what happens on every commit:

sequenceDiagram
    autonumber
    actor U as User
    participant UI as Coder UI
    participant S as coderd
    participant DB as Database
    participant A as Workspace agent
    participant G as git
    participant C as coder binary (gitsign-ssh)

    rect rgba(127,127,127,0.1)
    Note over U,DB: One-time setup
    U->>UI: Check "Sign my commits with my Coder SSH key"
    UI->>S: PUT /api/v2/users/me/preferences
    S->>DB: Save sign_commits_with_ssh_key = true
    end

    rect rgba(127,127,127,0.1)
    Note over S,A: Each time the agent connects, for example after a restart
    A->>S: GetManifest (dRPC, Agent API v2.17)
    S->>DB: Experiment on? Read preference and public key
    S-->>A: Manifest with git_signing_public_key
    A->>A: Add 5 GIT_CONFIG_* env entries to new sessions
    end

    rect rgba(127,127,127,0.1)
    Note over U,C: Every commit or tag
    U->>G: git commit
    G->>C: coder -Y sign -n git -f PUBKEY -U BUFFER
    C->>S: GET /api/v2/workspaceagents/me/gitsshkey (agent token, same as coder gitssh)
    S-->>C: Key pair
    C->>C: Hash BUFFER with SHA-512 and sign SSHSIG in memory
    C->>G: Write BUFFER.sig
    G->>G: Embed signature in the commit object
    end

Which sessions sign:

flowchart TD
    start([New session in the workspace]) --> exp{git-commit-signing experiment on?}
    exp -- No --> none[No signing config. git behaves as usual]
    exp -- Yes --> pref{User checked Sign my commits?}
    pref -- No --> none
    pref -- Yes --> sign[GIT_CONFIG_* set: commit.gpgsign, tag.gpgsign, gpg.format=ssh, gpg.ssh.program=coder, user.signingkey]
    sign --> commit[git commit and git tag are signed in the workspace]

• Setting: a new sign_commits_with_ssh_key user preference in user_configs (no migration), exposed through the existing preferences API.
• Manifest: when the experiment and the setting are both on, the agent manifest carries the owner's public key in a new git_signing_public_key field. The Agent API is bumped to v2.17 for it.
• Agent: agent/agentgitsign injects the config through GIT_CONFIG_COUNT/GIT_CONFIG_KEY_n/GIT_CONFIG_VALUE_n, appended after any count the template already set.
• No wrapper: gpg.ssh.program is the coder binary itself. Git runs it with ssh-keygen style arguments, and RunWithSubcommands sends any -Y ... invocation to the hidden gitsign-ssh command. No coder command takes -Y.
• Signing: gitsign-ssh fetches the key pair with the existing GET /api/v2/workspaceagents/me/gitsshkey, parses it, hashes the payload with SHA-512, signs an SSHSIG blob in memory, and writes <payload>.sig. Verification operations pass through to ssh-keygen unchanged, exit code included.
• UI: the checkbox only appears when the experiment is enabled. The * wildcard only enables safe experiments.

• Key exposure: signing happens in the workspace with the same key the agent can already fetch for git push/pull. This adds no new exposure, but it doesn't keep the key out of the workspace either; that would need a separate signing key no endpoint returns.
• Precedence: environment config overrides the user's own signing config, including commit.gpgsign=false. This is acceptable for an opt-in setting.
• Timing: the agent reads the setting when it connects, so turning it on or off takes effect after the next agent connect, for example a workspace restart.
• Key rotation: rotating the key (coder publickey --reset) means new commits need the new key registered with the git provider.
• Windows: expected to work, since nothing in the path is OS-specific, but untested.
• Docs: none, because unsafe experiments don't need docs under docs/.style/content-guidelines.md.

• Signer: agent/agentgitsign SSHSIG signatures verify with ssh-keygen -Y verify for ed25519, ECDSA and RSA. A signature made for git is rejected under another namespace.
• CLI: tests cover signing end to end against the existing gitsshkey endpoint (verified with ssh-keygen), verification pass-through, argument parsing and -Y dispatch.
• Manifest: tests cover gating on the experiment and the setting.
• Agent: tests check the env block and that an existing GIT_CONFIG_COUNT is preserved.
• Frontend: a Vitest test for the toggle, plus Storybook stories.