feat: add ssh_signing_key input for SSH commit signing (#784)

* feat: add ssh_signing_key input for SSH commit signing Add a new ssh_signing_key input that allows passing an SSH signing key for commit signing, as an alternative to the existing use_commit_signing (which uses GitHub API-based commits). When ssh_signing_key is provided: - Git is configured to use SSH signing (gpg.format=ssh, commit.gpgsign=true) - The key is written to ~/.ssh/claude_signing_key with 0600 permissions - Git CLI commands are used (not MCP file ops) - The key is cleaned up in a post step for security Behavior matrix: | ssh_signing_key | use_commit_signing | Result | |-----------------|-------------------|--------| | not set | false | Regular git, no signing | | not set | true | GitHub API (MCP), verified commits | | set | false | Git CLI with SSH signing | | set | true | Git CLI with SSH signing (ssh_signing_key takes precedence) * docs: add SSH signing key documentation - Update security.md with detailed setup instructions for both signing options - Explain that ssh_signing_key enables full git CLI operations (rebasing, etc.) - Add ssh_signing_key to inputs table in usage.md - Update bot_id/bot_name descriptions to note they're needed for verified commits * fix: address security review feedback for SSH signing - Write SSH key atomically with mode 0o600 (fixes TOCTOU race condition) - Create .ssh directory with mode 0o700 (SSH best practices) - Add input validation for SSH key format - Remove unused chmod import - Add tests for validation logic
2026-01-22 14:24:13 +08:00 · 2026-01-02 10:37:25 -08:00
parent 154d0de144
commit 7e4bf87b1c
14 changed files with 458 additions and 12 deletions
--- a/action.yml
+++ b/action.yml
@@ -81,6 +81,10 @@ inputs:
    description: "Enable commit signing using GitHub's commit signature verification. When false, Claude uses standard git commands"
    required: false
    default: "false"
+  ssh_signing_key:
+    description: "SSH private key for signing commits. When provided, git will be configured to use SSH signing. Takes precedence over use_commit_signing."
+    required: false
+    default: ""
  bot_id:
    description: "GitHub user ID to use for git operations (defaults to Claude's bot ID)"
    required: false
@@ -181,6 +185,7 @@ runs:
        USE_STICKY_COMMENT: ${{ inputs.use_sticky_comment }}
        DEFAULT_WORKFLOW_TOKEN: ${{ github.token }}
        USE_COMMIT_SIGNING: ${{ inputs.use_commit_signing }}
+        SSH_SIGNING_KEY: ${{ inputs.ssh_signing_key }}
        BOT_ID: ${{ inputs.bot_id }}
        BOT_NAME: ${{ inputs.bot_name }}
        TRACK_PROGRESS: ${{ inputs.track_progress }}
@@ -334,6 +339,12 @@ runs:
          echo '```' >> $GITHUB_STEP_SUMMARY
        fi

+    - name: Cleanup SSH signing key
+      if: always() && inputs.ssh_signing_key != ''
+      shell: bash
+      run: |
+        bun run ${GITHUB_ACTION_PATH}/src/entrypoints/cleanup-ssh-signing.ts
+
    - name: Revoke app token
      if: always() && inputs.github_token == '' && steps.prepare.outputs.skipped_due_to_workflow_validation_mismatch != 'true'
      shell: bash
--- a/docs/security.md
+++ b/docs/security.md
@@ -38,7 +38,64 @@ The following permissions are requested but not yet actively used. These will en

 ## Commit Signing

-Commits made by Claude through this action are no longer automatically signed with commit signatures. To enable commit signing set `use_commit_signing: True` in the workflow(s). This ensures the authenticity and integrity of commits, providing a verifiable trail of changes made by the action.
+By default, commits made by Claude are unsigned. You can enable commit signing using one of two methods:
+
+### Option 1: GitHub API Commit Signing (use_commit_signing)
+
+This uses GitHub's API to create commits, which automatically signs them as verified from the GitHub App:
+
+```yaml
+- uses: anthropics/claude-code-action@main
+  with:
+    use_commit_signing: true
+```
+
+This is the simplest option and requires no additional setup. However, because it uses the GitHub API instead of git CLI, it cannot perform complex git operations like rebasing, cherry-picking, or interactive history manipulation.
+
+### Option 2: SSH Signing Key (ssh_signing_key)
+
+This uses an SSH key to sign commits via git CLI. Use this option when you need both signed commits AND standard git operations (rebasing, cherry-picking, etc.):
+
+```yaml
+- uses: anthropics/claude-code-action@main
+  with:
+    ssh_signing_key: ${{ secrets.SSH_SIGNING_KEY }}
+    bot_id: "YOUR_GITHUB_USER_ID"
+    bot_name: "YOUR_GITHUB_USERNAME"
+```
+
+Commits will show as verified and attributed to the GitHub account that owns the signing key.
+
+**Setup steps:**
+
+1. Generate an SSH key pair for signing:
+
+   ```bash
+   ssh-keygen -t ed25519 -f ~/.ssh/signing_key -N "" -C "commit signing key"
+   ```
+
+2. Add the **public key** to your GitHub account:
+
+   - Go to GitHub → Settings → SSH and GPG keys
+   - Click "New SSH key"
+   - Select **Key type: Signing Key** (important)
+   - Paste the contents of `~/.ssh/signing_key.pub`
+
+3. Add the **private key** to your repository secrets:
+
+   - Go to your repo → Settings → Secrets and variables → Actions
+   - Create a new secret named `SSH_SIGNING_KEY`
+   - Paste the contents of `~/.ssh/signing_key`
+
+4. Get your GitHub user ID:
+
+   ```bash
+   gh api users/YOUR_USERNAME --jq '.id'
+   ```
+
+5. Update your workflow with `bot_id` and `bot_name` matching the account where you added the signing key.
+
+**Note:** If both `ssh_signing_key` and `use_commit_signing` are provided, `ssh_signing_key` takes precedence.

 ## ⚠️ Authentication Protection

--- a/docs/usage.md
+++ b/docs/usage.md
@@ -71,9 +71,10 @@ jobs:
 | `branch_prefix`                  | The prefix to use for Claude branches (defaults to 'claude/', use 'claude-' for dash format)                                                                                           | No       | `claude/`     |
 | `settings`                       | Claude Code settings as JSON string or path to settings JSON file                                                                                                                      | No       | ""            |
 | `additional_permissions`         | Additional permissions to enable. Currently supports 'actions: read' for viewing workflow results                                                                                      | No       | ""            |
-| `use_commit_signing`             | Enable commit signing using GitHub's commit signature verification. When false, Claude uses standard git commands                                                                      | No       | `false`       |
-| `bot_id`                         | GitHub user ID to use for git operations (defaults to Claude's bot ID)                                                                                                                 | No       | `41898282`    |
-| `bot_name`                       | GitHub username to use for git operations (defaults to Claude's bot name)                                                                                                              | No       | `claude[bot]` |
+| `use_commit_signing`             | Enable commit signing using GitHub's API. Simple but cannot perform complex git operations like rebasing. See [Security](./security.md#commit-signing)                                 | No       | `false`       |
+| `ssh_signing_key`                | SSH private key for signing commits. Enables signed commits with full git CLI support (rebasing, etc.). See [Security](./security.md#commit-signing)                                   | No       | ""            |
+| `bot_id`                         | GitHub user ID to use for git operations (defaults to Claude's bot ID). Required with `ssh_signing_key` for verified commits                                                           | No       | `41898282`    |
+| `bot_name`                       | GitHub username to use for git operations (defaults to Claude's bot name). Required with `ssh_signing_key` for verified commits                                                        | No       | `claude[bot]` |
 | `allowed_bots`                   | Comma-separated list of allowed bot usernames, or '\*' to allow all bots. Empty string (default) allows no bots                                                                        | No       | ""            |
 | `allowed_non_write_users`        | **⚠️ RISKY**: Comma-separated list of usernames to allow without write permissions, or '\*' for all users. Only works with `github_token` input. See [Security](./security.md)         | No       | ""            |
 | `path_to_claude_code_executable` | Optional path to a custom Claude Code executable. Skips automatic installation. Useful for Nix, custom containers, or specialized environments                                         | No       | ""            |
--- a/src/entrypoints/cleanup-ssh-signing.ts
+++ b/src/entrypoints/cleanup-ssh-signing.ts
@@ -0,0 +1,21 @@
+#!/usr/bin/env bun
+
+/**
+ * Cleanup SSH signing key after action completes
+ * This is run as a post step for security purposes
+ */
+
+import { cleanupSshSigning } from "../github/operations/git-config";
+
+async function run() {
+  try {
+    await cleanupSshSigning();
+  } catch (error) {
+    // Don't fail the action if cleanup fails, just log it
+    console.error("Failed to cleanup SSH signing key:", error);
+  }
+}
+
+if (import.meta.main) {
+  run();
+}
--- a/src/entrypoints/collect-inputs.ts
+++ b/src/entrypoints/collect-inputs.ts
@@ -26,6 +26,7 @@ export function collectActionInputsPresence(): void {
    max_turns: "",
    use_sticky_comment: "false",
    use_commit_signing: "false",
+    ssh_signing_key: "",
  };

  const allInputsJson = process.env.ALL_INPUTS;
--- a/src/github/context.ts
+++ b/src/github/context.ts
@@ -90,6 +90,7 @@ type BaseContext = {
    branchPrefix: string;
    useStickyComment: boolean;
    useCommitSigning: boolean;
+    sshSigningKey: string;
    botId: string;
    botName: string;
    allowedBots: string;
@@ -146,6 +147,7 @@ export function parseGitHubContext(): GitHubContext {
      branchPrefix: process.env.BRANCH_PREFIX ?? "claude/",
      useStickyComment: process.env.USE_STICKY_COMMENT === "true",
      useCommitSigning: process.env.USE_COMMIT_SIGNING === "true",
+      sshSigningKey: process.env.SSH_SIGNING_KEY || "",
      botId: process.env.BOT_ID ?? String(CLAUDE_APP_BOT_ID),
      botName: process.env.BOT_NAME ?? CLAUDE_BOT_LOGIN,
      allowedBots: process.env.ALLOWED_BOTS ?? "",
--- a/src/github/operations/git-config.ts
+++ b/src/github/operations/git-config.ts
@@ -6,9 +6,14 @@
 */

 import { $ } from "bun";
+import { mkdir, writeFile, rm } from "fs/promises";
+import { join } from "path";
+import { homedir } from "os";
 import type { GitHubContext } from "../context";
 import { GITHUB_SERVER_URL } from "../api/config";

+const SSH_SIGNING_KEY_PATH = join(homedir(), ".ssh", "claude_signing_key");
+
 type GitUser = {
  login: string;
  id: number;
@@ -54,3 +59,50 @@ export async function configureGitAuth(

  console.log("Git authentication configured successfully");
 }
+
+/**
+ * Configure git to use SSH signing for commits
+ * This is an alternative to GitHub API-based commit signing (use_commit_signing)
+ */
+export async function setupSshSigning(sshSigningKey: string): Promise<void> {
+  console.log("Configuring SSH signing for commits...");
+
+  // Validate SSH key format
+  if (!sshSigningKey.trim()) {
+    throw new Error("SSH signing key cannot be empty");
+  }
+  if (
+    !sshSigningKey.includes("BEGIN") ||
+    !sshSigningKey.includes("PRIVATE KEY")
+  ) {
+    throw new Error("Invalid SSH private key format");
+  }
+
+  // Create .ssh directory with secure permissions (700)
+  const sshDir = join(homedir(), ".ssh");
+  await mkdir(sshDir, { recursive: true, mode: 0o700 });
+
+  // Write the signing key atomically with secure permissions (600)
+  await writeFile(SSH_SIGNING_KEY_PATH, sshSigningKey, { mode: 0o600 });
+  console.log(`✓ SSH signing key written to ${SSH_SIGNING_KEY_PATH}`);
+
+  // Configure git to use SSH signing
+  await $`git config gpg.format ssh`;
+  await $`git config user.signingkey ${SSH_SIGNING_KEY_PATH}`;
+  await $`git config commit.gpgsign true`;
+
+  console.log("✓ Git configured to use SSH signing for commits");
+}
+
+/**
+ * Clean up the SSH signing key file
+ * Should be called in the post step for security
+ */
+export async function cleanupSshSigning(): Promise<void> {
+  try {
+    await rm(SSH_SIGNING_KEY_PATH, { force: true });
+    console.log("✓ SSH signing key cleaned up");
+  } catch (error) {
+    console.log("No SSH signing key to clean up");
+  }
+}
--- a/src/modes/agent/index.ts
+++ b/src/modes/agent/index.ts
@@ -4,7 +4,10 @@ import type { Mode, ModeOptions, ModeResult } from "../types";
 import type { PreparedContext } from "../../create-prompt/types";
 import { prepareMcpConfig } from "../../mcp/install-mcp-server";
 import { parseAllowedTools } from "./parse-tools";
-import { configureGitAuth } from "../../github/operations/git-config";
+import {
+  configureGitAuth,
+  setupSshSigning,
+} from "../../github/operations/git-config";
 import type { GitHubContext } from "../../github/context";
 import { isEntityContext } from "../../github/context";

@@ -79,7 +82,27 @@ export const agentMode: Mode = {

  async prepare({ context, githubToken }: ModeOptions): Promise<ModeResult> {
    // Configure git authentication for agent mode (same as tag mode)
-    if (!context.inputs.useCommitSigning) {
+    // SSH signing takes precedence if provided
+    const useSshSigning = !!context.inputs.sshSigningKey;
+    const useApiCommitSigning =
+      context.inputs.useCommitSigning && !useSshSigning;
+
+    if (useSshSigning) {
+      // Setup SSH signing for commits
+      await setupSshSigning(context.inputs.sshSigningKey);
+
+      // Still configure git auth for push operations (user/email and remote URL)
+      const user = {
+        login: context.inputs.botName,
+        id: parseInt(context.inputs.botId),
+      };
+      try {
+        await configureGitAuth(githubToken, context, user);
+      } catch (error) {
+        console.error("Failed to configure git authentication:", error);
+        // Continue anyway - git operations may still work with default config
+      }
+    } else if (!useApiCommitSigning) {
      // Use bot_id and bot_name from inputs directly
      const user = {
        login: context.inputs.botName,
--- a/src/modes/tag/index.ts
+++ b/src/modes/tag/index.ts
@@ -4,7 +4,10 @@ import { checkContainsTrigger } from "../../github/validation/trigger";
 import { checkHumanActor } from "../../github/validation/actor";
 import { createInitialComment } from "../../github/operations/comments/create-initial";
 import { setupBranch } from "../../github/operations/branch";
-import { configureGitAuth } from "../../github/operations/git-config";
+import {
+  configureGitAuth,
+  setupSshSigning,
+} from "../../github/operations/git-config";
 import { prepareMcpConfig } from "../../mcp/install-mcp-server";
 import {
  fetchGitHubData,
@@ -88,8 +91,28 @@ export const tagMode: Mode = {
    // Setup branch
    const branchInfo = await setupBranch(octokit, githubData, context);

-    // Configure git authentication if not using commit signing
-    if (!context.inputs.useCommitSigning) {
+    // Configure git authentication
+    // SSH signing takes precedence if provided
+    const useSshSigning = !!context.inputs.sshSigningKey;
+    const useApiCommitSigning =
+      context.inputs.useCommitSigning && !useSshSigning;
+
+    if (useSshSigning) {
+      // Setup SSH signing for commits
+      await setupSshSigning(context.inputs.sshSigningKey);
+
+      // Still configure git auth for push operations (user/email and remote URL)
+      const user = {
+        login: context.inputs.botName,
+        id: parseInt(context.inputs.botId),
+      };
+      try {
+        await configureGitAuth(githubToken, context, user);
+      } catch (error) {
+        console.error("Failed to configure git authentication:", error);
+        throw error;
+      }
+    } else if (!useApiCommitSigning) {
      // Use bot_id and bot_name from inputs directly
      const user = {
        login: context.inputs.botName,
@@ -135,8 +158,9 @@ export const tagMode: Mode = {
      ...userAllowedMCPTools,
    ];

-    // Add git commands when not using commit signing
-    if (!context.inputs.useCommitSigning) {
+    // Add git commands when using git CLI (no API commit signing, or SSH signing)
+    // SSH signing still uses git CLI, just with signing enabled
+    if (!useApiCommitSigning) {
      tagModeTools.push(
        "Bash(git add:*)",
        "Bash(git commit:*)",
@@ -147,7 +171,7 @@ export const tagMode: Mode = {
        "Bash(git rm:*)",
      );
    } else {
-      // When using commit signing, use MCP file ops tools
+      // When using API commit signing, use MCP file ops tools
      tagModeTools.push(
        "mcp__github_file_ops__commit_files",
        "mcp__github_file_ops__delete_files",
--- a/test/install-mcp-server.test.ts
+++ b/test/install-mcp-server.test.ts
@@ -32,6 +32,7 @@ describe("prepareMcpConfig", () => {
      branchPrefix: "",
      useStickyComment: false,
      useCommitSigning: false,
+      sshSigningKey: "",
      botId: String(CLAUDE_APP_BOT_ID),
      botName: CLAUDE_BOT_LOGIN,
      allowedBots: "",
--- a/test/mockContext.ts
+++ b/test/mockContext.ts
@@ -20,6 +20,7 @@ const defaultInputs = {
  branchPrefix: "claude/",
  useStickyComment: false,
  useCommitSigning: false,
+  sshSigningKey: "",
  botId: String(CLAUDE_APP_BOT_ID),
  botName: CLAUDE_BOT_LOGIN,
  allowedBots: "",
--- a/test/modes/detector.test.ts
+++ b/test/modes/detector.test.ts
@@ -20,6 +20,7 @@ describe("detectMode with enhanced routing", () => {
      branchPrefix: "claude/",
      useStickyComment: false,
      useCommitSigning: false,
+      sshSigningKey: "",
      botId: "123456",
      botName: "claude-bot",
      allowedBots: "",
--- a/test/permissions.test.ts
+++ b/test/permissions.test.ts
@@ -68,6 +68,7 @@ describe("checkWritePermissions", () => {
      branchPrefix: "claude/",
      useStickyComment: false,
      useCommitSigning: false,
+      sshSigningKey: "",
      botId: String(CLAUDE_APP_BOT_ID),
      botName: CLAUDE_BOT_LOGIN,
      allowedBots: "",
--- a/test/ssh-signing.test.ts
+++ b/test/ssh-signing.test.ts
@@ -0,0 +1,250 @@
+#!/usr/bin/env bun
+
+import {
+  describe,
+  test,
+  expect,
+  afterEach,
+  beforeAll,
+  afterAll,
+} from "bun:test";
+import { mkdir, writeFile, rm, readFile, stat } from "fs/promises";
+import { join } from "path";
+import { tmpdir } from "os";
+
+describe("SSH Signing", () => {
+  // Use a temp directory for tests
+  const testTmpDir = join(tmpdir(), "claude-ssh-signing-test");
+  const testSshDir = join(testTmpDir, ".ssh");
+  const testKeyPath = join(testSshDir, "claude_signing_key");
+  const testKey =
+    "-----BEGIN OPENSSH PRIVATE KEY-----\ntest-key-content\n-----END OPENSSH PRIVATE KEY-----";
+
+  beforeAll(async () => {
+    await mkdir(testTmpDir, { recursive: true });
+  });
+
+  afterAll(async () => {
+    await rm(testTmpDir, { recursive: true, force: true });
+  });
+
+  afterEach(async () => {
+    // Clean up test key if it exists
+    try {
+      await rm(testKeyPath, { force: true });
+    } catch {
+      // Ignore cleanup errors
+    }
+  });
+
+  describe("setupSshSigning file operations", () => {
+    test("should write key file atomically with correct permissions", async () => {
+      // Create the directory with secure permissions (same as setupSshSigning does)
+      await mkdir(testSshDir, { recursive: true, mode: 0o700 });
+
+      // Write key atomically with proper permissions (same as setupSshSigning does)
+      await writeFile(testKeyPath, testKey, { mode: 0o600 });
+
+      // Verify key was written
+      const keyContent = await readFile(testKeyPath, "utf-8");
+      expect(keyContent).toBe(testKey);
+
+      // Verify permissions (0o600 = 384 in decimal for permission bits only)
+      const stats = await stat(testKeyPath);
+      const permissions = stats.mode & 0o777; // Get only permission bits
+      expect(permissions).toBe(0o600);
+    });
+
+    test("should create .ssh directory with secure permissions", async () => {
+      // Clean up first
+      await rm(testSshDir, { recursive: true, force: true });
+
+      // Create directory with secure permissions (same as setupSshSigning does)
+      await mkdir(testSshDir, { recursive: true, mode: 0o700 });
+
+      // Verify directory exists
+      const dirStats = await stat(testSshDir);
+      expect(dirStats.isDirectory()).toBe(true);
+
+      // Verify directory permissions
+      const dirPermissions = dirStats.mode & 0o777;
+      expect(dirPermissions).toBe(0o700);
+    });
+  });
+
+  describe("setupSshSigning validation", () => {
+    test("should reject empty SSH key", () => {
+      const emptyKey = "";
+      expect(() => {
+        if (!emptyKey.trim()) {
+          throw new Error("SSH signing key cannot be empty");
+        }
+      }).toThrow("SSH signing key cannot be empty");
+    });
+
+    test("should reject whitespace-only SSH key", () => {
+      const whitespaceKey = "   \n\t  ";
+      expect(() => {
+        if (!whitespaceKey.trim()) {
+          throw new Error("SSH signing key cannot be empty");
+        }
+      }).toThrow("SSH signing key cannot be empty");
+    });
+
+    test("should reject invalid SSH key format", () => {
+      const invalidKey = "not a valid key";
+      expect(() => {
+        if (
+          !invalidKey.includes("BEGIN") ||
+          !invalidKey.includes("PRIVATE KEY")
+        ) {
+          throw new Error("Invalid SSH private key format");
+        }
+      }).toThrow("Invalid SSH private key format");
+    });
+
+    test("should accept valid SSH key format", () => {
+      const validKey =
+        "-----BEGIN OPENSSH PRIVATE KEY-----\nkey-content\n-----END OPENSSH PRIVATE KEY-----";
+      expect(() => {
+        if (!validKey.trim()) {
+          throw new Error("SSH signing key cannot be empty");
+        }
+        if (!validKey.includes("BEGIN") || !validKey.includes("PRIVATE KEY")) {
+          throw new Error("Invalid SSH private key format");
+        }
+      }).not.toThrow();
+    });
+  });
+
+  describe("cleanupSshSigning file operations", () => {
+    test("should remove the signing key file", async () => {
+      // Create the key file first
+      await mkdir(testSshDir, { recursive: true });
+      await writeFile(testKeyPath, testKey, { mode: 0o600 });
+
+      // Verify it exists
+      const existsBefore = await stat(testKeyPath)
+        .then(() => true)
+        .catch(() => false);
+      expect(existsBefore).toBe(true);
+
+      // Clean up (same operation as cleanupSshSigning)
+      await rm(testKeyPath, { force: true });
+
+      // Verify it's gone
+      const existsAfter = await stat(testKeyPath)
+        .then(() => true)
+        .catch(() => false);
+      expect(existsAfter).toBe(false);
+    });
+
+    test("should not throw if key file does not exist", async () => {
+      // Make sure file doesn't exist
+      await rm(testKeyPath, { force: true });
+
+      // Should not throw (rm with force: true doesn't throw on missing files)
+      await expect(rm(testKeyPath, { force: true })).resolves.toBeUndefined();
+    });
+  });
+});
+
+describe("SSH Signing Mode Detection", () => {
+  test("sshSigningKey should take precedence over useCommitSigning", () => {
+    // When both are set, SSH signing takes precedence
+    const sshSigningKey = "test-key";
+    const useCommitSigning = true;
+
+    const useSshSigning = !!sshSigningKey;
+    const useApiCommitSigning = useCommitSigning && !useSshSigning;
+
+    expect(useSshSigning).toBe(true);
+    expect(useApiCommitSigning).toBe(false);
+  });
+
+  test("useCommitSigning should work when sshSigningKey is not set", () => {
+    const sshSigningKey = "";
+    const useCommitSigning = true;
+
+    const useSshSigning = !!sshSigningKey;
+    const useApiCommitSigning = useCommitSigning && !useSshSigning;
+
+    expect(useSshSigning).toBe(false);
+    expect(useApiCommitSigning).toBe(true);
+  });
+
+  test("neither signing method when both are false/empty", () => {
+    const sshSigningKey = "";
+    const useCommitSigning = false;
+
+    const useSshSigning = !!sshSigningKey;
+    const useApiCommitSigning = useCommitSigning && !useSshSigning;
+
+    expect(useSshSigning).toBe(false);
+    expect(useApiCommitSigning).toBe(false);
+  });
+
+  test("git CLI tools should be used when sshSigningKey is set", () => {
+    // This tests the logic in tag mode for tool selection
+    const sshSigningKey = "test-key";
+    const useCommitSigning = true; // Even if this is true
+
+    const useSshSigning = !!sshSigningKey;
+    const useApiCommitSigning = useCommitSigning && !useSshSigning;
+
+    // When SSH signing is used, we should use git CLI (not API)
+    const shouldUseGitCli = !useApiCommitSigning;
+    expect(shouldUseGitCli).toBe(true);
+  });
+
+  test("MCP file ops should only be used with API commit signing", () => {
+    // Case 1: API commit signing
+    {
+      const sshSigningKey = "";
+      const useCommitSigning = true;
+
+      const useSshSigning = !!sshSigningKey;
+      const useApiCommitSigning = useCommitSigning && !useSshSigning;
+
+      expect(useApiCommitSigning).toBe(true);
+    }
+
+    // Case 2: SSH signing (should NOT use API)
+    {
+      const sshSigningKey = "test-key";
+      const useCommitSigning = true;
+
+      const useSshSigning = !!sshSigningKey;
+      const useApiCommitSigning = useCommitSigning && !useSshSigning;
+
+      expect(useApiCommitSigning).toBe(false);
+    }
+
+    // Case 3: No signing (should NOT use API)
+    {
+      const sshSigningKey = "";
+      const useCommitSigning = false;
+
+      const useSshSigning = !!sshSigningKey;
+      const useApiCommitSigning = useCommitSigning && !useSshSigning;
+
+      expect(useApiCommitSigning).toBe(false);
+    }
+  });
+});
+
+describe("Context parsing", () => {
+  test("sshSigningKey should be parsed from environment", () => {
+    // Test that context.ts parses SSH_SIGNING_KEY correctly
+    const testCases = [
+      { env: "test-key", expected: "test-key" },
+      { env: "", expected: "" },
+      { env: undefined, expected: "" },
+    ];
+
+    for (const { env, expected } of testCases) {
+      const result = env || "";
+      expect(result).toBe(expected);
+    }
+  });
+});