feat: add porcelain worktree parser with listWorktrees and parseWorktreeListPorcelain

Introduce git worktree list --porcelain parsing following upstream opencode patterns. Exports listWorktrees() for full worktree enumeration with branch info alongside existing detectWorktreePath().

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/start-work/worktree-detector.test.ts

@@ -2,7 +2,7 @@
 
 import { describe, expect, test, spyOn, beforeEach, afterEach } from "bun:test"
 import * as childProcess from "node:child_process"
-import { detectWorktreePath } from "./worktree-detector"
+import { detectWorktreePath, parseWorktreeListPorcelain, listWorktrees } from "./worktree-detector"
 
 describe("detectWorktreePath", () => {
   let execFileSyncSpy: ReturnType<typeof spyOn>
@@ -77,3 +77,113 @@ describe("detectWorktreePath", () => {
     })
   })
 })
+
+describe("parseWorktreeListPorcelain", () => {
+  test("#given porcelain output with multiple worktrees #when parsing #then returns all entries", () => {
+    // given
+    const output = [
+      "worktree /home/user/main-repo",
+      "HEAD abc1234",
+      "branch refs/heads/main",
+      "",
+      "worktree /home/user/worktrees/feature-a",
+      "HEAD def5678",
+      "branch refs/heads/feature-a",
+      "",
+    ].join("\n")
+
+    // when
+    const result = parseWorktreeListPorcelain(output)
+
+    // then
+    expect(result).toEqual([
+      { path: "/home/user/main-repo", branch: "main", bare: false },
+      { path: "/home/user/worktrees/feature-a", branch: "feature-a", bare: false },
+    ])
+  })
+
+  test("#given bare worktree #when parsing #then marks bare flag", () => {
+    // given
+    const output = [
+      "worktree /home/user/bare-repo",
+      "HEAD abc1234",
+      "bare",
+      "",
+    ].join("\n")
+
+    // when
+    const result = parseWorktreeListPorcelain(output)
+
+    // then
+    expect(result).toEqual([
+      { path: "/home/user/bare-repo", branch: undefined, bare: true },
+    ])
+  })
+
+  test("#given empty output #when parsing #then returns empty array", () => {
+    expect(parseWorktreeListPorcelain("")).toEqual([])
+  })
+
+  test("#given output without trailing newline #when parsing #then still captures last entry", () => {
+    // given
+    const output = [
+      "worktree /repo",
+      "HEAD abc1234",
+      "branch refs/heads/dev",
+    ].join("\n")
+
+    // when
+    const result = parseWorktreeListPorcelain(output)
+
+    // then
+    expect(result).toEqual([
+      { path: "/repo", branch: "dev", bare: false },
+    ])
+  })
+})
+
+describe("listWorktrees", () => {
+  let execFileSyncSpy: ReturnType<typeof spyOn>
+
+  beforeEach(() => {
+    execFileSyncSpy = spyOn(childProcess, "execFileSync").mockImplementation(
+      ((_file: string, _args: string[]) => "") as typeof childProcess.execFileSync,
+    )
+  })
+
+  afterEach(() => {
+    execFileSyncSpy.mockRestore()
+  })
+
+  test("#given valid git repo #when listing #then returns parsed worktree entries", () => {
+    // given
+    execFileSyncSpy.mockImplementation(
+      ((_file: string, _args: string[]) =>
+        "worktree /repo\nHEAD abc\nbranch refs/heads/main\n\n") as typeof childProcess.execFileSync,
+    )
+
+    // when
+    const result = listWorktrees("/repo")
+
+    // then
+    expect(result).toEqual([{ path: "/repo", branch: "main", bare: false }])
+    expect(execFileSyncSpy).toHaveBeenCalledWith(
+      "git",
+      ["worktree", "list", "--porcelain"],
+      expect.objectContaining({ cwd: "/repo" }),
+    )
+  })
+
+  test("#given non-git directory #when listing #then returns empty array", () => {
+    // given
+    execFileSyncSpy.mockImplementation((_file: string, _args: string[]) => {
+      throw new Error("not a git repository")
+    })
+
+    // when
+    const result = listWorktrees("/tmp/not-a-repo")
+
+    // then
+    expect(result).toEqual([])
+  })
+})