diff --git a/src/lib/vcs/__tests__/types.test.ts b/src/lib/vcs/__tests__/types.test.ts
new file mode 100644
index 00000000..0bc55b4a
--- /dev/null
+++ b/src/lib/vcs/__tests__/types.test.ts
@@ -0,0 +1,295 @@
+import { describe, it, expect } from 'vitest';
+import type {
+  Workspace,
+  WorkspaceResult,
+  MergeResult,
+  RebaseResult,
+  DeleteBranchOptions,
+  DeleteBranchResult,
+  PushOptions,
+  FinalizeTemplateVars,
+  FinalizeCommands,
+  VcsConfig,
+} from '../types.js';
+
+// ── AC-I-002-1: Workspace can replace Worktree from git.ts ──────────────
+
+describe('Workspace type', () => {
+  it('has all fields required by Worktree (backward compat)', () => {
+    const ws: Workspace = {
+      path: '/tmp/worktrees/bd-deoi',
+      branch: 'foreman/bd-deoi',
+      head: 'abc123def456',
+      bare: false,
+    };
+    expect(ws.path).toBe('/tmp/worktrees/bd-deoi');
+    expect(ws.branch).toBe('foreman/bd-deoi');
+    expect(ws.head).toBe('abc123def456');
+    expect(ws.bare).toBe(false);
+  });
+
+  it('accepts a jj change ID as head', () => {
+    const ws: Workspace = {
+      path: '/tmp/jj-workspace',
+      branch: 'trunk()',
+      head: 'yklonqvs',   // jj short change ID
+      bare: false,
+    };
+    expect(ws.head).toBe('yklonqvs');
+  });
+
+  it('accepts a jj bookmark name as branch', () => {
+    const ws: Workspace = {
+      path: '/tmp/jj-workspace',
+      branch: 'my-bookmark',
+      head: 'abc',
+      bare: false,
+    };
+    expect(ws.branch).toBe('my-bookmark');
+  });
+
+  it('bare field is required and boolean', () => {
+    const ws: Workspace = { path: '/', branch: 'main', head: 'a1b2c3', bare: false };
+    expect(typeof ws.bare).toBe('boolean');
+  });
+});
+
+// ── WorkspaceResult ─────────────────────────────────────────────────────
+
+describe('WorkspaceResult type', () => {
+  it('has workspacePath and branchName', () => {
+    const result: WorkspaceResult = {
+      workspacePath: '/tmp/worktrees/bd-deoi',
+      branchName: 'foreman/bd-deoi',
+    };
+    expect(result.workspacePath).toContain('bd-deoi');
+    expect(result.branchName).toBe('foreman/bd-deoi');
+  });
+});
+
+// ── MergeResult ─────────────────────────────────────────────────────────
+
+describe('MergeResult type', () => {
+  it('success:true has no conflicts', () => {
+    const result: MergeResult = { success: true };
+    expect(result.success).toBe(true);
+    expect(result.conflicts).toBeUndefined();
+  });
+
+  it('success:false can have conflicts array', () => {
+    const result: MergeResult = {
+      success: false,
+      conflicts: ['src/lib/git.ts', 'package.json'],
+    };
+    expect(result.conflicts).toHaveLength(2);
+  });
+
+  it('conflicts field is optional', () => {
+    const minimal: MergeResult = { success: false };
+    expect(minimal.conflicts).toBeUndefined();
+  });
+});
+
+// ── RebaseResult ────────────────────────────────────────────────────────
+
+describe('RebaseResult type', () => {
+  it('clean rebase has no conflicting files', () => {
+    const result: RebaseResult = { success: true, hasConflicts: false };
+    expect(result.conflictingFiles).toBeUndefined();
+  });
+
+  it('conflict rebase includes conflictingFiles', () => {
+    const result: RebaseResult = {
+      success: false,
+      hasConflicts: true,
+      conflictingFiles: ['src/lib/git.ts'],
+    };
+    expect(result.hasConflicts).toBe(true);
+    expect(result.conflictingFiles).toContain('src/lib/git.ts');
+  });
+
+  it('conflictingFiles is optional', () => {
+    const result: RebaseResult = { success: false, hasConflicts: true };
+    expect(result.conflictingFiles).toBeUndefined();
+  });
+});
+
+// ── DeleteBranchOptions ─────────────────────────────────────────────────
+
+describe('DeleteBranchOptions type', () => {
+  it('both fields are optional', () => {
+    const opts: DeleteBranchOptions = {};
+    expect(opts.force).toBeUndefined();
+    expect(opts.targetBranch).toBeUndefined();
+  });
+
+  it('accepts force and targetBranch', () => {
+    const opts: DeleteBranchOptions = { force: true, targetBranch: 'dev' };
+    expect(opts.force).toBe(true);
+    expect(opts.targetBranch).toBe('dev');
+  });
+});
+
+// ── DeleteBranchResult ──────────────────────────────────────────────────
+
+describe('DeleteBranchResult type', () => {
+  it('has required boolean fields', () => {
+    const result: DeleteBranchResult = { deleted: true, wasFullyMerged: true };
+    expect(typeof result.deleted).toBe('boolean');
+    expect(typeof result.wasFullyMerged).toBe('boolean');
+  });
+
+  it('can represent a force-deleted unmerged branch', () => {
+    const result: DeleteBranchResult = { deleted: true, wasFullyMerged: false };
+    expect(result.deleted).toBe(true);
+    expect(result.wasFullyMerged).toBe(false);
+  });
+});
+
+// ── PushOptions ─────────────────────────────────────────────────────────
+
+describe('PushOptions type', () => {
+  it('all fields are optional', () => {
+    const opts: PushOptions = {};
+    expect(opts.force).toBeUndefined();
+    expect(opts.allowNew).toBeUndefined();
+  });
+
+  it('accepts jj-specific allowNew', () => {
+    const opts: PushOptions = { allowNew: true };
+    expect(opts.allowNew).toBe(true);
+  });
+
+  it('accepts force push', () => {
+    const opts: PushOptions = { force: true };
+    expect(opts.force).toBe(true);
+  });
+});
+
+// ── FinalizeTemplateVars ────────────────────────────────────────────────
+
+describe('FinalizeTemplateVars type', () => {
+  it('has all required fields', () => {
+    const vars: FinalizeTemplateVars = {
+      seedId: 'bd-deoi',
+      seedTitle: 'Define Shared VCS Types',
+      baseBranch: 'dev',
+      worktreePath: '/tmp/worktrees/bd-deoi',
+    };
+    expect(vars.seedId).toBe('bd-deoi');
+    expect(vars.baseBranch).toBe('dev');
+  });
+});
+
+// ── AC-I-002-2: FinalizeCommands has all 6 required fields ──────────────
+
+describe('FinalizeCommands type', () => {
+  it('has all 6 required fields', () => {
+    const cmds: FinalizeCommands = {
+      stageCommand: 'git add -A',
+      commitCommand: 'git commit -m "feat: implement task"',
+      pushCommand: 'git push origin foreman/bd-deoi',
+      rebaseCommand: 'git rebase origin/dev',
+      branchVerifyCommand: 'git ls-remote --heads origin foreman/bd-deoi',
+      cleanCommand: 'git worktree remove /tmp/worktrees/bd-deoi',
+    };
+    // Verify all 6 are present and string-typed
+    expect(typeof cmds.stageCommand).toBe('string');
+    expect(typeof cmds.commitCommand).toBe('string');
+    expect(typeof cmds.pushCommand).toBe('string');
+    expect(typeof cmds.rebaseCommand).toBe('string');
+    expect(typeof cmds.branchVerifyCommand).toBe('string');
+    expect(typeof cmds.cleanCommand).toBe('string');
+  });
+
+  it('accepts empty strings for no-op commands (e.g. jj auto-staging)', () => {
+    const cmds: FinalizeCommands = {
+      stageCommand: '',    // jj auto-stages
+      commitCommand: 'jj commit -m "feat: implement task"',
+      pushCommand: 'jj git push --allow-new',
+      rebaseCommand: 'jj rebase -d main',
+      branchVerifyCommand: 'jj bookmark list',
+      cleanCommand: 'jj workspace forget foreman-bd-deoi',
+    };
+    expect(cmds.stageCommand).toBe('');
+  });
+});
+
+// ── VcsConfig ───────────────────────────────────────────────────────────
+
+describe('VcsConfig type', () => {
+  it('backend is required and must be git | jujutsu | auto', () => {
+    const cfgGit: VcsConfig = { backend: 'git' };
+    const cfgJj: VcsConfig = { backend: 'jujutsu' };
+    const cfgAuto: VcsConfig = { backend: 'auto' };
+    expect(cfgGit.backend).toBe('git');
+    expect(cfgJj.backend).toBe('jujutsu');
+    expect(cfgAuto.backend).toBe('auto');
+  });
+
+  it('git and jujutsu sub-configs are optional', () => {
+    const cfg: VcsConfig = { backend: 'auto' };
+    expect(cfg.git).toBeUndefined();
+    expect(cfg.jujutsu).toBeUndefined();
+  });
+
+  it('accepts git useTown option', () => {
+    const cfg: VcsConfig = { backend: 'git', git: { useTown: true } };
+    expect(cfg.git?.useTown).toBe(true);
+  });
+
+  it('accepts jujutsu minVersion option', () => {
+    const cfg: VcsConfig = { backend: 'jujutsu', jujutsu: { minVersion: '0.25.0' } };
+    expect(cfg.jujutsu?.minVersion).toBe('0.25.0');
+  });
+
+  it('useTown and minVersion are optional within sub-configs', () => {
+    const cfg: VcsConfig = { backend: 'git', git: {} };
+    expect(cfg.git?.useTown).toBeUndefined();
+  });
+});
+
+// ── AC-I-002-3: Both GitBackend and JujutsuBackend can use all types ─────
+
+describe('Type compatibility across backends', () => {
+  it('Workspace works for a git backend scenario', () => {
+    // Simulating what GitBackend.createWorkspace() would return
+    const gitWorkspace: Workspace = {
+      path: '/tmp/worktrees/bd-deoi',
+      branch: 'foreman/bd-deoi',
+      head: '7c3d2e1f4a8b',   // git SHA
+      bare: false,
+    };
+    const result: WorkspaceResult = {
+      workspacePath: gitWorkspace.path,
+      branchName: gitWorkspace.branch,
+    };
+    expect(result.branchName).toBe('foreman/bd-deoi');
+  });
+
+  it('Workspace works for a jujutsu backend scenario', () => {
+    // Simulating what JujutsuBackend.createWorkspace() would return
+    const jjWorkspace: Workspace = {
+      path: '/tmp/jj-workspace/bd-deoi',
+      branch: 'foreman/bd-deoi',   // jj bookmark name
+      head: 'yklonqvs',             // jj short change ID
+      bare: false,
+    };
+    expect(jjWorkspace.head.length).toBeLessThan(40);  // jj IDs are shorter than git SHAs
+  });
+
+  it('MergeResult is usable by both backends', () => {
+    const gitMerge: MergeResult = { success: true };
+    const jjMerge: MergeResult = { success: false, conflicts: ['src/lib/git.ts'] };
+    expect(gitMerge.success).toBe(true);
+    expect(jjMerge.conflicts).toBeDefined();
+  });
+
+  it('PushOptions allowNew is usable by jj, ignorable by git', () => {
+    // Both backends accept the same PushOptions shape
+    const gitPushOpts: PushOptions = { force: false };
+    const jjPushOpts: PushOptions = { force: false, allowNew: true };
+    expect(gitPushOpts.allowNew).toBeUndefined();  // git ignores it
+    expect(jjPushOpts.allowNew).toBe(true);
+  });
+});
diff --git a/src/lib/vcs/types.ts b/src/lib/vcs/types.ts
new file mode 100644
index 00000000..54190f33
--- /dev/null
+++ b/src/lib/vcs/types.ts
@@ -0,0 +1,124 @@
+/**
+ * Shared VCS types for backend-agnostic workspace and operation representations.
+ * These types serve as the data contract for all VCS backend implementations
+ * (GitBackend, JujutsuBackend) and their consumers throughout Foreman.
+ *
+ * @module src/lib/vcs/types
+ */
+
+/** Replaces Worktree from git.ts. Backend-agnostic workspace representation. */
+export interface Workspace {
+  /** Absolute filesystem path to the workspace/worktree directory. */
+  path: string;
+  /** git branch name or jj bookmark name */
+  branch: string;
+  /** git commit hash or jj change ID */
+  head: string;
+  /** Always false for jj workspaces; may be true for git bare worktrees. */
+  bare: boolean;
+}
+
+/** Result of a createWorkspace() operation. */
+export interface WorkspaceResult {
+  /** Absolute path to the created workspace directory. */
+  workspacePath: string;
+  /** Branch/bookmark name created for this workspace; format: 'foreman/<seedId>' for both backends. */
+  branchName: string;
+}
+
+/** Result of a merge operation. */
+export interface MergeResult {
+  /** True if the merge completed without conflicts. */
+  success: boolean;
+  /** List of files with conflicts, if any. Omitted when merge succeeds cleanly. */
+  conflicts?: string[];
+}
+
+/** Result of a rebase operation. */
+export interface RebaseResult {
+  /** True if the rebase completed successfully. */
+  success: boolean;
+  /** True if the rebase encountered conflicts that require resolution. */
+  hasConflicts: boolean;
+  /** List of files with conflicts. Present only when hasConflicts is true. */
+  conflictingFiles?: string[];
+}
+
+/** Options for delete branch/bookmark operations. */
+export interface DeleteBranchOptions {
+  /** If true, force-delete even if not fully merged (equivalent to git branch -D). */
+  force?: boolean;
+  /**
+   * The target/base branch to check merge status against.
+   * Defaults to the repository's default branch if omitted.
+   */
+  targetBranch?: string;
+}
+
+/** Result of a delete branch/bookmark operation. */
+export interface DeleteBranchResult {
+  /** True if the branch/bookmark was successfully deleted. */
+  deleted: boolean;
+  /** True if the branch had been fully merged into the target before deletion. */
+  wasFullyMerged: boolean;
+}
+
+/** Options for push operations. */
+export interface PushOptions {
+  /** If true, force-push (overwrite remote history). Use with caution. */
+  force?: boolean;
+  /**
+   * Jujutsu-specific: passes --allow-new flag to allow pushing new bookmarks.
+   * GitBackend ignores this field.
+   */
+  allowNew?: boolean;
+}
+
+/** Template variables for backend-specific finalize command generation. */
+export interface FinalizeTemplateVars {
+  /** The seed/bead ID for this task (e.g. 'bd-deoi'). */
+  seedId: string;
+  /** Human-readable title of the seed/task. */
+  seedTitle: string;
+  /** The base branch to rebase onto (e.g. 'dev' or 'main'). */
+  baseBranch: string;
+  /** Absolute path to the worktree/workspace directory. */
+  worktreePath: string;
+}
+
+/**
+ * Backend-specific finalize commands for prompt rendering.
+ * The Finalize agent uses these pre-computed commands in its prompt so it
+ * doesn't need to know which VCS backend is in use. All fields are required;
+ * use an empty string for commands that are no-ops on a given backend.
+ */
+export interface FinalizeCommands {
+  /** Command to stage all changes (e.g. 'git add -A'). Empty string for backends with auto-staging (jj). */
+  stageCommand: string;
+  /** Command to commit staged changes with an appropriate message. */
+  commitCommand: string;
+  /** Command to push the branch/bookmark to the remote. */
+  pushCommand: string;
+  /** Command to rebase the workspace branch onto the base branch. */
+  rebaseCommand: string;
+  /** Command to verify the branch/bookmark exists on the remote after push. */
+  branchVerifyCommand: string;
+  /** Command to clean up the workspace after finalization. */
+  cleanCommand: string;
+}
+
+/** VCS configuration read from project config YAML (.foreman/config.yaml). */
+export interface VcsConfig {
+  /** Which VCS backend to use. 'auto' detects based on repository contents. */
+  backend: 'git' | 'jujutsu' | 'auto';
+  /** Git-specific configuration options. */
+  git?: {
+    /** If true, use git-town for branch management operations. Default: true. */
+    useTown?: boolean;
+  };
+  /** Jujutsu-specific configuration options. */
+  jujutsu?: {
+    /** Minimum jj version required; validated by 'foreman doctor'. */
+    minVersion?: string;
+  };
+}