diff --git a/src/hooks/atlas/index.ts b/src/hooks/atlas/index.ts
index ffad04598..b2608187e 100644
--- a/src/hooks/atlas/index.ts
+++ b/src/hooks/atlas/index.ts
@@ -1,5 +1,4 @@
 import type { PluginInput } from "@opencode-ai/plugin"
-import { execSync } from "node:child_process"
 import { existsSync, readdirSync } from "node:fs"
 import { join } from "node:path"
 import {
@@ -12,6 +11,7 @@ import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../../features/ho
 import { log } from "../../shared/logger"
 import { createSystemDirective, SYSTEM_DIRECTIVE_PREFIX, SystemDirectiveTypes } from "../../shared/system-directive"
 import { isCallerOrchestrator, getMessageDir } from "../../shared/session-utils"
+import { collectGitDiffStats, formatFileChanges } from "../../shared/git-worktree"
 import type { BackgroundManager } from "../../features/background-agent"
 
 export const HOOK_NAME = "atlas"
@@ -269,113 +269,6 @@ function extractSessionIdFromOutput(output: string): string {
   return match?.[1] ?? "<session_id>"
 }
 
-interface GitFileStat {
-  path: string
-  added: number
-  removed: number
-  status: "modified" | "added" | "deleted"
-}
-
-function getGitDiffStats(directory: string): GitFileStat[] {
-  try {
-    const output = execSync("git diff --numstat HEAD", {
-      cwd: directory,
-      encoding: "utf-8",
-      timeout: 5000,
-      stdio: ["pipe", "pipe", "pipe"],
-    }).trim()
-
-    if (!output) return []
-
-    const statusOutput = execSync("git status --porcelain", {
-      cwd: directory,
-      encoding: "utf-8",
-      timeout: 5000,
-      stdio: ["pipe", "pipe", "pipe"],
-    }).trim()
-
-    const statusMap = new Map<string, "modified" | "added" | "deleted">()
-    for (const line of statusOutput.split("\n")) {
-      if (!line) continue
-      const status = line.substring(0, 2).trim()
-      const filePath = line.substring(3)
-      if (status === "A" || status === "??") {
-        statusMap.set(filePath, "added")
-      } else if (status === "D") {
-        statusMap.set(filePath, "deleted")
-      } else {
-        statusMap.set(filePath, "modified")
-      }
-    }
-
-    const stats: GitFileStat[] = []
-    for (const line of output.split("\n")) {
-      const parts = line.split("\t")
-      if (parts.length < 3) continue
-
-      const [addedStr, removedStr, path] = parts
-      const added = addedStr === "-" ? 0 : parseInt(addedStr, 10)
-      const removed = removedStr === "-" ? 0 : parseInt(removedStr, 10)
-
-      stats.push({
-        path,
-        added,
-        removed,
-        status: statusMap.get(path) ?? "modified",
-      })
-    }
-
-    return stats
-  } catch {
-    return []
-  }
-}
-
-function formatFileChanges(stats: GitFileStat[], notepadPath?: string): string {
-  if (stats.length === 0) return "[FILE CHANGES SUMMARY]\nNo file changes detected.\n"
-
-  const modified = stats.filter((s) => s.status === "modified")
-  const added = stats.filter((s) => s.status === "added")
-  const deleted = stats.filter((s) => s.status === "deleted")
-
-  const lines: string[] = ["[FILE CHANGES SUMMARY]"]
-
-  if (modified.length > 0) {
-    lines.push("Modified files:")
-    for (const f of modified) {
-      lines.push(`  ${f.path}  (+${f.added}, -${f.removed})`)
-    }
-    lines.push("")
-  }
-
-  if (added.length > 0) {
-    lines.push("Created files:")
-    for (const f of added) {
-      lines.push(`  ${f.path}  (+${f.added})`)
-    }
-    lines.push("")
-  }
-
-  if (deleted.length > 0) {
-    lines.push("Deleted files:")
-    for (const f of deleted) {
-      lines.push(`  ${f.path}  (-${f.removed})`)
-    }
-    lines.push("")
-  }
-
-  if (notepadPath) {
-    const notepadStat = stats.find((s) => s.path.includes("notepad") || s.path.includes(".sisyphus"))
-    if (notepadStat) {
-      lines.push("[NOTEPAD UPDATED]")
-      lines.push(`  ${notepadStat.path}  (+${notepadStat.added})`)
-      lines.push("")
-    }
-  }
-
-  return lines.join("\n")
-}
-
 interface ToolExecuteAfterInput {
   tool: string
   sessionID?: string
@@ -750,8 +643,8 @@ export function createAtlasHook(
       }
       
       if (output.output && typeof output.output === "string") {
-        const gitStats = getGitDiffStats(ctx.directory)
-        const fileChanges = formatFileChanges(gitStats)
+    const gitStats = collectGitDiffStats(ctx.directory)
+    const fileChanges = formatFileChanges(gitStats)
         const subagentSessionId = extractSessionIdFromOutput(output.output)
 
         const boulderState = readBoulderState(ctx.directory)
diff --git a/src/shared/git-worktree/collect-git-diff-stats.ts b/src/shared/git-worktree/collect-git-diff-stats.ts
new file mode 100644
index 000000000..158a09d82
--- /dev/null
+++ b/src/shared/git-worktree/collect-git-diff-stats.ts
@@ -0,0 +1,29 @@
+import { execSync } from "node:child_process"
+import { parseGitStatusPorcelain } from "./parse-status-porcelain"
+import { parseGitDiffNumstat } from "./parse-diff-numstat"
+import type { GitFileStat } from "./types"
+
+export function collectGitDiffStats(directory: string): GitFileStat[] {
+  try {
+    const diffOutput = execSync("git diff --numstat HEAD", {
+      cwd: directory,
+      encoding: "utf-8",
+      timeout: 5000,
+      stdio: ["pipe", "pipe", "pipe"],
+    }).trim()
+
+    if (!diffOutput) return []
+
+    const statusOutput = execSync("git status --porcelain", {
+      cwd: directory,
+      encoding: "utf-8",
+      timeout: 5000,
+      stdio: ["pipe", "pipe", "pipe"],
+    }).trim()
+
+    const statusMap = parseGitStatusPorcelain(statusOutput)
+    return parseGitDiffNumstat(diffOutput, statusMap)
+  } catch {
+    return []
+  }
+}
diff --git a/src/shared/git-worktree/format-file-changes.ts b/src/shared/git-worktree/format-file-changes.ts
new file mode 100644
index 000000000..5afb58b8c
--- /dev/null
+++ b/src/shared/git-worktree/format-file-changes.ts
@@ -0,0 +1,46 @@
+import type { GitFileStat } from "./types"
+
+export function formatFileChanges(stats: GitFileStat[], notepadPath?: string): string {
+  if (stats.length === 0) return "[FILE CHANGES SUMMARY]\nNo file changes detected.\n"
+
+  const modified = stats.filter((s) => s.status === "modified")
+  const added = stats.filter((s) => s.status === "added")
+  const deleted = stats.filter((s) => s.status === "deleted")
+
+  const lines: string[] = ["[FILE CHANGES SUMMARY]"]
+
+  if (modified.length > 0) {
+    lines.push("Modified files:")
+    for (const f of modified) {
+      lines.push(`  ${f.path}  (+${f.added}, -${f.removed})`)
+    }
+    lines.push("")
+  }
+
+  if (added.length > 0) {
+    lines.push("Created files:")
+    for (const f of added) {
+      lines.push(`  ${f.path}  (+${f.added})`)
+    }
+    lines.push("")
+  }
+
+  if (deleted.length > 0) {
+    lines.push("Deleted files:")
+    for (const f of deleted) {
+      lines.push(`  ${f.path}  (-${f.removed})`)
+    }
+    lines.push("")
+  }
+
+  if (notepadPath) {
+    const notepadStat = stats.find((s) => s.path.includes("notepad") || s.path.includes(".sisyphus"))
+    if (notepadStat) {
+      lines.push("[NOTEPAD UPDATED]")
+      lines.push(`  ${notepadStat.path}  (+${notepadStat.added})`)
+      lines.push("")
+    }
+  }
+
+  return lines.join("\n")
+}
diff --git a/src/shared/git-worktree/git-worktree.test.ts b/src/shared/git-worktree/git-worktree.test.ts
new file mode 100644
index 000000000..27183018b
--- /dev/null
+++ b/src/shared/git-worktree/git-worktree.test.ts
@@ -0,0 +1,51 @@
+/// <reference types="bun-types" />
+
+import { describe, expect, test } from "bun:test"
+import { formatFileChanges, parseGitDiffNumstat, parseGitStatusPorcelain } from "./index"
+
+describe("git-worktree", () => {
+  test("#given status porcelain output #when parsing #then maps paths to statuses", () => {
+    const porcelain = [
+      " M src/a.ts",
+      "A  src/b.ts",
+      "?? src/c.ts",
+      "D  src/d.ts",
+    ].join("\n")
+
+    const map = parseGitStatusPorcelain(porcelain)
+    expect(map.get("src/a.ts")).toBe("modified")
+    expect(map.get("src/b.ts")).toBe("added")
+    expect(map.get("src/c.ts")).toBe("added")
+    expect(map.get("src/d.ts")).toBe("deleted")
+  })
+
+  test("#given diff numstat and status map #when parsing #then returns typed stats", () => {
+    const porcelain = [" M src/a.ts", "A  src/b.ts"].join("\n")
+    const statusMap = parseGitStatusPorcelain(porcelain)
+
+    const numstat = ["1\t2\tsrc/a.ts", "3\t0\tsrc/b.ts", "-\t-\tbin.dat"].join("\n")
+    const stats = parseGitDiffNumstat(numstat, statusMap)
+
+    expect(stats).toEqual([
+      { path: "src/a.ts", added: 1, removed: 2, status: "modified" },
+      { path: "src/b.ts", added: 3, removed: 0, status: "added" },
+      { path: "bin.dat", added: 0, removed: 0, status: "modified" },
+    ])
+  })
+
+  test("#given git file stats #when formatting #then produces grouped summary", () => {
+    const summary = formatFileChanges([
+      { path: "src/a.ts", added: 1, removed: 2, status: "modified" },
+      { path: "src/b.ts", added: 3, removed: 0, status: "added" },
+      { path: "src/c.ts", added: 0, removed: 4, status: "deleted" },
+    ])
+
+    expect(summary).toContain("[FILE CHANGES SUMMARY]")
+    expect(summary).toContain("Modified files:")
+    expect(summary).toContain("Created files:")
+    expect(summary).toContain("Deleted files:")
+    expect(summary).toContain("src/a.ts")
+    expect(summary).toContain("src/b.ts")
+    expect(summary).toContain("src/c.ts")
+  })
+})
diff --git a/src/shared/git-worktree/index.ts b/src/shared/git-worktree/index.ts
new file mode 100644
index 000000000..0bc363d0f
--- /dev/null
+++ b/src/shared/git-worktree/index.ts
@@ -0,0 +1,5 @@
+export type { GitFileStatus, GitFileStat } from "./types"
+export { parseGitStatusPorcelain } from "./parse-status-porcelain"
+export { parseGitDiffNumstat } from "./parse-diff-numstat"
+export { collectGitDiffStats } from "./collect-git-diff-stats"
+export { formatFileChanges } from "./format-file-changes"
diff --git a/src/shared/git-worktree/parse-diff-numstat.ts b/src/shared/git-worktree/parse-diff-numstat.ts
new file mode 100644
index 000000000..3ea2b0f6d
--- /dev/null
+++ b/src/shared/git-worktree/parse-diff-numstat.ts
@@ -0,0 +1,27 @@
+import type { GitFileStat, GitFileStatus } from "./types"
+
+export function parseGitDiffNumstat(
+  output: string,
+  statusMap: Map<string, GitFileStatus>
+): GitFileStat[] {
+  if (!output) return []
+
+  const stats: GitFileStat[] = []
+  for (const line of output.split("\n")) {
+    const parts = line.split("\t")
+    if (parts.length < 3) continue
+
+    const [addedStr, removedStr, path] = parts
+    const added = addedStr === "-" ? 0 : parseInt(addedStr, 10)
+    const removed = removedStr === "-" ? 0 : parseInt(removedStr, 10)
+
+    stats.push({
+      path,
+      added,
+      removed,
+      status: statusMap.get(path) ?? "modified",
+    })
+  }
+
+  return stats
+}
diff --git a/src/shared/git-worktree/parse-status-porcelain.ts b/src/shared/git-worktree/parse-status-porcelain.ts
new file mode 100644
index 000000000..0623de5d9
--- /dev/null
+++ b/src/shared/git-worktree/parse-status-porcelain.ts
@@ -0,0 +1,25 @@
+import type { GitFileStatus } from "./types"
+
+export function parseGitStatusPorcelain(output: string): Map<string, GitFileStatus> {
+  const map = new Map<string, GitFileStatus>()
+  if (!output) return map
+
+  for (const line of output.split("\n")) {
+    if (!line) continue
+
+    const status = line.substring(0, 2).trim()
+    const filePath = line.substring(3)
+
+    if (!filePath) continue
+
+    if (status === "A" || status === "??") {
+      map.set(filePath, "added")
+    } else if (status === "D") {
+      map.set(filePath, "deleted")
+    } else {
+      map.set(filePath, "modified")
+    }
+  }
+
+  return map
+}
diff --git a/src/shared/git-worktree/types.ts b/src/shared/git-worktree/types.ts
new file mode 100644
index 000000000..eb4236990
--- /dev/null
+++ b/src/shared/git-worktree/types.ts
@@ -0,0 +1,8 @@
+export type GitFileStatus = "modified" | "added" | "deleted"
+
+export interface GitFileStat {
+  path: string
+  added: number
+  removed: number
+  status: GitFileStatus
+}
diff --git a/src/shared/index.ts b/src/shared/index.ts
index d42be5a75..4ea346972 100644
--- a/src/shared/index.ts
+++ b/src/shared/index.ts
@@ -41,5 +41,6 @@ export * from "./tmux"
 export * from "./model-suggestion-retry"
 export * from "./opencode-server-auth"
 export * from "./port-utils"
+export * from "./git-worktree"
 export * from "./safe-create-hook"
 export * from "./truncate-description"