diff --git a/packages/opencode/src/project/vcs.ts b/packages/opencode/src/project/vcs.ts
index dea25b91b4..e3243ba8eb 100644
--- a/packages/opencode/src/project/vcs.ts
+++ b/packages/opencode/src/project/vcs.ts
@@ -1,17 +1,111 @@
 import { Effect, Layer, ServiceMap } from "effect"
+import path from "path"
 import { Bus } from "@/bus"
 import { BusEvent } from "@/bus/bus-event"
 import { InstanceState } from "@/effect/instance-state"
 import { makeRunPromise } from "@/effect/run-service"
+import { AppFileSystem } from "@/filesystem"
 import { FileWatcher } from "@/file/watcher"
+import { Git } from "@/git"
+import { Snapshot } from "@/snapshot"
 import { Log } from "@/util/log"
-import { git } from "@/util/git"
 import { Instance } from "./instance"
 import z from "zod"
 
 export namespace Vcs {
   const log = Log.create({ service: "vcs" })
 
+  const count = (text: string) => {
+    if (!text) return 0
+    if (!text.endsWith("\n")) return text.split("\n").length
+    return text.slice(0, -1).split("\n").length
+  }
+
+  const work = Effect.fnUntraced(function* (fs: AppFileSystem.Interface, cwd: string, file: string) {
+    const full = path.join(cwd, file)
+    if (!(yield* fs.exists(full).pipe(Effect.orDie))) return ""
+    const buf = yield* fs.readFile(full).pipe(Effect.catch(() => Effect.succeed(new Uint8Array())))
+    if (Buffer.from(buf).includes(0)) return ""
+    return Buffer.from(buf).toString("utf8")
+  })
+
+  const nums = (list: Git.Stat[]) =>
+    new Map(list.map((item) => [item.file, { additions: item.additions, deletions: item.deletions }] as const))
+
+  const merge = (...lists: Git.Item[][]) => {
+    const out = new Map<string, Git.Item>()
+    lists.flat().forEach((item) => {
+      if (!out.has(item.file)) out.set(item.file, item)
+    })
+    return [...out.values()]
+  }
+
+  const files = Effect.fnUntraced(function* (
+    fs: AppFileSystem.Interface,
+    git: Git.Interface,
+    cwd: string,
+    ref: string | undefined,
+    list: Git.Item[],
+    map: Map<string, { additions: number; deletions: number }>,
+  ) {
+    const base = ref ? yield* git.prefix(cwd) : ""
+    const next = yield* Effect.forEach(
+      list,
+      (item) =>
+        Effect.gen(function* () {
+          const before = item.status === "added" || !ref ? "" : yield* git.show(cwd, ref, item.file, base)
+          const after = item.status === "deleted" ? "" : yield* work(fs, cwd, item.file)
+          const stat = map.get(item.file)
+          return {
+            file: item.file,
+            before,
+            after,
+            additions: stat?.additions ?? (item.status === "added" ? count(after) : 0),
+            deletions: stat?.deletions ?? (item.status === "deleted" ? count(before) : 0),
+            status: item.status,
+          } satisfies Snapshot.FileDiff
+        }),
+      { concurrency: 8 },
+    )
+    return next.toSorted((a, b) => a.file.localeCompare(b.file))
+  })
+
+  const track = Effect.fnUntraced(function* (
+    fs: AppFileSystem.Interface,
+    git: Git.Interface,
+    cwd: string,
+    ref: string | undefined,
+  ) {
+    if (!ref) return yield* files(fs, git, cwd, ref, yield* git.status(cwd), new Map())
+    const [list, stats] = yield* Effect.all([git.status(cwd), git.stats(cwd, ref)], { concurrency: 2 })
+    return yield* files(fs, git, cwd, ref, list, nums(stats))
+  })
+
+  const compare = Effect.fnUntraced(function* (
+    fs: AppFileSystem.Interface,
+    git: Git.Interface,
+    cwd: string,
+    ref: string,
+  ) {
+    const [list, stats, extra] = yield* Effect.all([git.diff(cwd, ref), git.stats(cwd, ref), git.status(cwd)], {
+      concurrency: 3,
+    })
+    return yield* files(
+      fs,
+      git,
+      cwd,
+      ref,
+      merge(
+        list,
+        extra.filter((item) => item.code === "??"),
+      ),
+      nums(stats),
+    )
+  })
+
+  export const Mode = z.enum(["git", "branch"])
+  export type Mode = z.infer<typeof Mode>
+
   export const Event = {
     BranchUpdated: BusEvent.define(
       "vcs.branch.updated",
@@ -23,7 +117,8 @@ export namespace Vcs {
 
   export const Info = z
     .object({
-      branch: z.string(),
+      branch: z.string().optional(),
+      default_branch: z.string().optional(),
     })
     .meta({
       ref: "VcsInfo",
@@ -33,37 +128,35 @@ export namespace Vcs {
   export interface Interface {
     readonly init: () => Effect.Effect<void>
     readonly branch: () => Effect.Effect<string | undefined>
+    readonly defaultBranch: () => Effect.Effect<string | undefined>
+    readonly diff: (mode: Mode) => Effect.Effect<Snapshot.FileDiff[]>
   }
 
   interface State {
     current: string | undefined
+    root: Git.Base | undefined
   }
 
   export class Service extends ServiceMap.Service<Service, Interface>()("@opencode/Vcs") {}
 
-  export const layer = Layer.effect(
+  export const layer: Layer.Layer<Service, never, AppFileSystem.Service | Git.Service> = Layer.effect(
     Service,
     Effect.gen(function* () {
+      const fs = yield* AppFileSystem.Service
+      const git = yield* Git.Service
       const state = yield* InstanceState.make<State>(
         Effect.fn("Vcs.state")((ctx) =>
           Effect.gen(function* () {
             if (ctx.project.vcs !== "git") {
-              return { current: undefined }
+              return { current: undefined, root: undefined }
             }
 
-            const getCurrentBranch = async () => {
-              const result = await git(["rev-parse", "--abbrev-ref", "HEAD"], {
-                cwd: ctx.worktree,
-              })
-              if (result.exitCode !== 0) return undefined
-              const text = result.text().trim()
-              return text || undefined
-            }
-
-            const value = {
-              current: yield* Effect.promise(() => getCurrentBranch()),
-            }
-            log.info("initialized", { branch: value.current })
+            const get = () => Effect.runPromise(git.branch(ctx.directory))
+            const [current, root] = yield* Effect.all([git.branch(ctx.directory), git.defaultBranch(ctx.directory)], {
+              concurrency: 2,
+            })
+            const value = { current, root }
+            log.info("initialized", { branch: value.current, default_branch: value.root?.name })
 
             yield* Effect.acquireRelease(
               Effect.sync(() =>
@@ -71,12 +164,11 @@ export namespace Vcs {
                   FileWatcher.Event.Updated,
                   Instance.bind(async (evt) => {
                     if (!evt.properties.file.endsWith("HEAD")) return
-                    const next = await getCurrentBranch()
-                    if (next !== value.current) {
-                      log.info("branch changed", { from: value.current, to: next })
-                      value.current = next
-                      Bus.publish(Event.BranchUpdated, { branch: next })
-                    }
+                    const next = await get()
+                    if (next === value.current) return
+                    log.info("branch changed", { from: value.current, to: next })
+                    value.current = next
+                    Bus.publish(Event.BranchUpdated, { branch: next })
                   }),
                 ),
               ),
@@ -95,11 +187,34 @@ export namespace Vcs {
         branch: Effect.fn("Vcs.branch")(function* () {
           return yield* InstanceState.use(state, (x) => x.current)
         }),
+        defaultBranch: Effect.fn("Vcs.defaultBranch")(function* () {
+          return yield* InstanceState.use(state, (x) => x.root?.name)
+        }),
+        diff: Effect.fn("Vcs.diff")(function* (mode: Mode) {
+          const value = yield* InstanceState.get(state)
+          if (Instance.project.vcs !== "git") return []
+          if (mode === "git") {
+            return yield* track(
+              fs,
+              git,
+              Instance.directory,
+              (yield* git.hasHead(Instance.directory)) ? "HEAD" : undefined,
+            )
+          }
+
+          if (!value.root) return []
+          if (value.current && value.current === value.root.name) return []
+          const ref = yield* git.mergeBase(Instance.directory, value.root.ref)
+          if (!ref) return []
+          return yield* compare(fs, git, Instance.directory, ref)
+        }),
       })
     }),
   )
 
-  const runPromise = makeRunPromise(Service, layer)
+  export const defaultLayer = layer.pipe(Layer.provide(Git.defaultLayer), Layer.provide(AppFileSystem.defaultLayer))
+
+  const runPromise = makeRunPromise(Service, defaultLayer)
 
   export function init() {
     return runPromise((svc) => svc.init())
@@ -108,4 +223,12 @@ export namespace Vcs {
   export function branch() {
     return runPromise((svc) => svc.branch())
   }
+
+  export function defaultBranch() {
+    return runPromise((svc) => svc.defaultBranch())
+  }
+
+  export function diff(mode: Mode) {
+    return runPromise((svc) => svc.diff(mode))
+  }
 }
diff --git a/packages/opencode/test/git/git.test.ts b/packages/opencode/test/git/git.test.ts
new file mode 100644
index 0000000000..a897a38e68
--- /dev/null
+++ b/packages/opencode/test/git/git.test.ts
@@ -0,0 +1,128 @@
+import { $ } from "bun"
+import { describe, expect, test } from "bun:test"
+import fs from "fs/promises"
+import path from "path"
+import { ManagedRuntime } from "effect"
+import { Git } from "../../src/git"
+import { tmpdir } from "../fixture/fixture"
+
+const weird = process.platform === "win32" ? "space file.txt" : "tab\tfile.txt"
+
+async function withGit<T>(body: (rt: ManagedRuntime.ManagedRuntime<Git.Service, never>) => Promise<T>) {
+  const rt = ManagedRuntime.make(Git.defaultLayer)
+  try {
+    return await body(rt)
+  } finally {
+    await rt.dispose()
+  }
+}
+
+describe("Git", () => {
+  test("branch() returns current branch name", async () => {
+    await using tmp = await tmpdir({ git: true })
+
+    await withGit(async (rt) => {
+      const branch = await rt.runPromise(Git.Service.use((git) => git.branch(tmp.path)))
+      expect(branch).toBeDefined()
+      expect(typeof branch).toBe("string")
+    })
+  })
+
+  test("branch() returns undefined for non-git directories", async () => {
+    await using tmp = await tmpdir()
+
+    await withGit(async (rt) => {
+      const branch = await rt.runPromise(Git.Service.use((git) => git.branch(tmp.path)))
+      expect(branch).toBeUndefined()
+    })
+  })
+
+  test("branch() returns undefined for detached HEAD", async () => {
+    await using tmp = await tmpdir({ git: true })
+    const hash = (await $`git rev-parse HEAD`.cwd(tmp.path).quiet().text()).trim()
+    await $`git checkout --detach ${hash}`.cwd(tmp.path).quiet()
+
+    await withGit(async (rt) => {
+      const branch = await rt.runPromise(Git.Service.use((git) => git.branch(tmp.path)))
+      expect(branch).toBeUndefined()
+    })
+  })
+
+  test("defaultBranch() uses init.defaultBranch when available", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await $`git branch -M trunk`.cwd(tmp.path).quiet()
+    await $`git config init.defaultBranch trunk`.cwd(tmp.path).quiet()
+
+    await withGit(async (rt) => {
+      const branch = await rt.runPromise(Git.Service.use((git) => git.defaultBranch(tmp.path)))
+      expect(branch?.name).toBe("trunk")
+      expect(branch?.ref).toBe("trunk")
+    })
+  })
+
+  test("status() handles special filenames", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await fs.writeFile(path.join(tmp.path, weird), "hello\n", "utf-8")
+
+    await withGit(async (rt) => {
+      const status = await rt.runPromise(Git.Service.use((git) => git.status(tmp.path)))
+      expect(status).toEqual(
+        expect.arrayContaining([
+          expect.objectContaining({
+            file: weird,
+            status: "added",
+          }),
+        ]),
+      )
+    })
+  })
+
+  test("diff(), stats(), and mergeBase() parse tracked changes", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await $`git branch -M main`.cwd(tmp.path).quiet()
+    await fs.writeFile(path.join(tmp.path, weird), "before\n", "utf-8")
+    await $`git add .`.cwd(tmp.path).quiet()
+    await $`git commit --no-gpg-sign -m "add file"`.cwd(tmp.path).quiet()
+    await $`git checkout -b feature/test`.cwd(tmp.path).quiet()
+    await fs.writeFile(path.join(tmp.path, weird), "after\n", "utf-8")
+
+    await withGit(async (rt) => {
+      const [base, diff, stats] = await Promise.all([
+        rt.runPromise(Git.Service.use((git) => git.mergeBase(tmp.path, "main"))),
+        rt.runPromise(Git.Service.use((git) => git.diff(tmp.path, "HEAD"))),
+        rt.runPromise(Git.Service.use((git) => git.stats(tmp.path, "HEAD"))),
+      ])
+
+      expect(base).toBeTruthy()
+      expect(diff).toEqual(
+        expect.arrayContaining([
+          expect.objectContaining({
+            file: weird,
+            status: "modified",
+          }),
+        ]),
+      )
+      expect(stats).toEqual(
+        expect.arrayContaining([
+          expect.objectContaining({
+            file: weird,
+            additions: 1,
+            deletions: 1,
+          }),
+        ]),
+      )
+    })
+  })
+
+  test("show() returns empty text for binary blobs", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await fs.writeFile(path.join(tmp.path, "bin.dat"), new Uint8Array([0, 1, 2, 3]))
+    await $`git add .`.cwd(tmp.path).quiet()
+    await $`git commit --no-gpg-sign -m "add binary"`.cwd(tmp.path).quiet()
+
+    await withGit(async (rt) => {
+      const text = await rt.runPromise(Git.Service.use((git) => git.show(tmp.path, "HEAD", "bin.dat")))
+      expect(text).toBe("")
+    })
+  })
+})
diff --git a/packages/opencode/test/project/vcs.test.ts b/packages/opencode/test/project/vcs.test.ts
index 11463b7950..f55989caff 100644
--- a/packages/opencode/test/project/vcs.test.ts
+++ b/packages/opencode/test/project/vcs.test.ts
@@ -23,7 +23,7 @@ function withVcs(
 ) {
   return withServices(
     directory,
-    Layer.merge(FileWatcher.layer, Vcs.layer),
+    Layer.merge(FileWatcher.layer, Vcs.defaultLayer),
     async (rt) => {
       await rt.runPromise(FileWatcher.Service.use((s) => s.init()))
       await rt.runPromise(Vcs.Service.use((s) => s.init()))
@@ -34,7 +34,15 @@ function withVcs(
   )
 }
 
+function withVcsOnly(
+  directory: string,
+  body: (rt: ManagedRuntime.ManagedRuntime<Vcs.Service, never>) => Promise<void>,
+) {
+  return withServices(directory, Vcs.defaultLayer, body)
+}
+
 type BranchEvent = { directory?: string; payload: { type: string; properties: { branch?: string } } }
+const weird = process.platform === "win32" ? "space file.txt" : "tab\tfile.txt"
 
 /** Wait for a Vcs.Event.BranchUpdated event on GlobalBus, with retry polling as fallback */
 function nextBranchUpdate(directory: string, timeout = 10_000) {
@@ -123,3 +131,105 @@ describeVcs("Vcs", () => {
     })
   })
 })
+
+describe("Vcs diff", () => {
+  afterEach(async () => {
+    await Instance.disposeAll()
+  })
+
+  test("defaultBranch() falls back to main", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await $`git branch -M main`.cwd(tmp.path).quiet()
+
+    await withVcsOnly(tmp.path, async (rt) => {
+      const branch = await rt.runPromise(Vcs.Service.use((s) => s.defaultBranch()))
+      expect(branch).toBe("main")
+    })
+  })
+
+  test("defaultBranch() uses init.defaultBranch when available", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await $`git branch -M trunk`.cwd(tmp.path).quiet()
+    await $`git config init.defaultBranch trunk`.cwd(tmp.path).quiet()
+
+    await withVcsOnly(tmp.path, async (rt) => {
+      const branch = await rt.runPromise(Vcs.Service.use((s) => s.defaultBranch()))
+      expect(branch).toBe("trunk")
+    })
+  })
+
+  test("detects current branch from the active worktree", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await using wt = await tmpdir()
+    await $`git branch -M main`.cwd(tmp.path).quiet()
+    const dir = path.join(wt.path, "feature")
+    await $`git worktree add -b feature/test ${dir} HEAD`.cwd(tmp.path).quiet()
+
+    await withVcsOnly(dir, async (rt) => {
+      const [branch, base] = await Promise.all([
+        rt.runPromise(Vcs.Service.use((s) => s.branch())),
+        rt.runPromise(Vcs.Service.use((s) => s.defaultBranch())),
+      ])
+      expect(branch).toBe("feature/test")
+      expect(base).toBe("main")
+    })
+  })
+
+  test("diff('git') returns uncommitted changes", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await fs.writeFile(path.join(tmp.path, "file.txt"), "original\n", "utf-8")
+    await $`git add .`.cwd(tmp.path).quiet()
+    await $`git commit --no-gpg-sign -m "add file"`.cwd(tmp.path).quiet()
+    await fs.writeFile(path.join(tmp.path, "file.txt"), "changed\n", "utf-8")
+
+    await withVcsOnly(tmp.path, async (rt) => {
+      const diff = await rt.runPromise(Vcs.Service.use((s) => s.diff("git")))
+      expect(diff).toEqual(
+        expect.arrayContaining([
+          expect.objectContaining({
+            file: "file.txt",
+            status: "modified",
+          }),
+        ]),
+      )
+    })
+  })
+
+  test("diff('git') handles special filenames", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await fs.writeFile(path.join(tmp.path, weird), "hello\n", "utf-8")
+
+    await withVcsOnly(tmp.path, async (rt) => {
+      const diff = await rt.runPromise(Vcs.Service.use((s) => s.diff("git")))
+      expect(diff).toEqual(
+        expect.arrayContaining([
+          expect.objectContaining({
+            file: weird,
+            status: "added",
+          }),
+        ]),
+      )
+    })
+  })
+
+  test("diff('branch') returns changes against default branch", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await $`git branch -M main`.cwd(tmp.path).quiet()
+    await $`git checkout -b feature/test`.cwd(tmp.path).quiet()
+    await fs.writeFile(path.join(tmp.path, "branch.txt"), "hello\n", "utf-8")
+    await $`git add .`.cwd(tmp.path).quiet()
+    await $`git commit --no-gpg-sign -m "branch file"`.cwd(tmp.path).quiet()
+
+    await withVcsOnly(tmp.path, async (rt) => {
+      const diff = await rt.runPromise(Vcs.Service.use((s) => s.diff("branch")))
+      expect(diff).toEqual(
+        expect.arrayContaining([
+          expect.objectContaining({
+            file: "branch.txt",
+            status: "added",
+          }),
+        ]),
+      )
+    })
+  })
+})