diff --git a/src/cli/install-codex/git-bash.test.ts b/src/cli/install-codex/git-bash.test.ts
new file mode 100644
index 000000000..5407052fd
--- /dev/null
+++ b/src/cli/install-codex/git-bash.test.ts
@@ -0,0 +1,118 @@
+/// <reference path="../../../bun-test.d.ts" />
+/// <reference types="bun-types" />
+
+import { describe, expect, test } from "bun:test"
+import { resolveGitBash } from "./git-bash"
+
+const PROGRAM_FILES_GIT_BASH = "C:\\Program Files\\Git\\bin\\bash.exe"
+const PROGRAM_FILES_X86_GIT_BASH = "C:\\Program Files (x86)\\Git\\bin\\bash.exe"
+
+describe("git-bash", () => {
+  test("#given non-Windows platform #when resolving Git Bash #then no preflight is required", () => {
+    // given / when
+    const result = resolveGitBash({
+      platform: "darwin",
+      env: {},
+      exists: () => false,
+      where: () => [],
+    })
+
+    // then
+    expect(result).toEqual({ found: true, path: null, source: "not-required" })
+  })
+
+  test("#given Windows env override to bash.exe #when the file exists #then env path wins", () => {
+    // given
+    const overridePath = "D:\\Tools\\Git\\bin\\bash.exe"
+
+    // when
+    const result = resolveGitBash({
+      platform: "win32",
+      env: { OMO_CODEX_GIT_BASH_PATH: overridePath },
+      exists: (path: string) => path === overridePath,
+      where: () => [PROGRAM_FILES_GIT_BASH],
+    })
+
+    // then
+    expect(result).toEqual({ found: true, path: overridePath, source: "env" })
+  })
+
+  test("#given Windows env override not pointing to bash.exe #when resolving #then reports invalid override and stops", () => {
+    // given
+    const overridePath = "D:\\Tools\\Git\\bin\\git.exe"
+
+    // when
+    const result = resolveGitBash({
+      platform: "win32",
+      env: { OMO_CODEX_GIT_BASH_PATH: overridePath },
+      exists: () => true,
+      where: () => [PROGRAM_FILES_GIT_BASH],
+    })
+
+    // then
+    expect(result.found).toBe(false)
+    if (result.found) return
+    expect(result.checkedPaths).toContain(overridePath)
+    expect(result.installHint).toContain("OMO_CODEX_GIT_BASH_PATH=C:\\path\\to\\bash.exe")
+  })
+
+  test("#given Windows standard 64-bit Git Bash exists #when resolving #then uses Program Files path", () => {
+    // given / when
+    const result = resolveGitBash({
+      platform: "win32",
+      env: {},
+      exists: (path: string) => path === PROGRAM_FILES_GIT_BASH,
+      where: () => [],
+    })
+
+    // then
+    expect(result).toEqual({ found: true, path: PROGRAM_FILES_GIT_BASH, source: "program-files" })
+  })
+
+  test("#given Windows standard 32-bit Git Bash exists #when resolving #then uses Program Files x86 path", () => {
+    // given / when
+    const result = resolveGitBash({
+      platform: "win32",
+      env: {},
+      exists: (path: string) => path === PROGRAM_FILES_X86_GIT_BASH,
+      where: () => [],
+    })
+
+    // then
+    expect(result).toEqual({ found: true, path: PROGRAM_FILES_X86_GIT_BASH, source: "program-files-x86" })
+  })
+
+  test("#given Windows bash on PATH #when standard paths are missing #then uses where bash candidate", () => {
+    // given
+    const pathCandidate = "E:\\Git\\bin\\bash.exe"
+
+    // when
+    const result = resolveGitBash({
+      platform: "win32",
+      env: {},
+      exists: (path: string) => path === pathCandidate,
+      where: () => ["C:\\Windows\\System32\\bash.exe", pathCandidate],
+    })
+
+    // then
+    expect(result).toEqual({ found: true, path: pathCandidate, source: "path" })
+  })
+
+  test("#given Windows without Git Bash #when resolving #then returns install guidance", () => {
+    // given / when
+    const result = resolveGitBash({
+      platform: "win32",
+      env: {},
+      exists: () => false,
+      where: () => [],
+    })
+
+    // then
+    expect(result.found).toBe(false)
+    if (result.found) return
+    expect(result.checkedPaths).toEqual([PROGRAM_FILES_GIT_BASH, PROGRAM_FILES_X86_GIT_BASH])
+    expect(result.installHint).toContain("winget install --id Git.Git -e --source winget")
+    expect(result.installHint).toContain("OMO_CODEX_GIT_BASH_PATH=C:\\path\\to\\bash.exe")
+    expect(result.installHint).toContain("rerun `bunx omo install --platform=codex`")
+  })
+})
diff --git a/src/cli/install-codex/git-bash.ts b/src/cli/install-codex/git-bash.ts
new file mode 100644
index 000000000..f0d75af25
--- /dev/null
+++ b/src/cli/install-codex/git-bash.ts
@@ -0,0 +1,104 @@
+import { execFileSync } from "node:child_process"
+import { existsSync } from "node:fs"
+
+const GIT_BASH_ENV_KEY = "OMO_CODEX_GIT_BASH_PATH"
+const PROGRAM_FILES_GIT_BASH = "C:\\Program Files\\Git\\bin\\bash.exe"
+const PROGRAM_FILES_X86_GIT_BASH = "C:\\Program Files (x86)\\Git\\bin\\bash.exe"
+
+export type GitBashSource = "not-required" | "env" | "program-files" | "program-files-x86" | "path"
+
+export type GitBashResolution =
+  | {
+    readonly found: true
+    readonly path: string | null
+    readonly source: GitBashSource
+  }
+  | {
+    readonly found: false
+    readonly checkedPaths: readonly string[]
+    readonly installHint: string
+  }
+
+export interface GitBashResolverInput {
+  readonly platform: string
+  readonly env: { readonly [key: string]: string | undefined }
+  readonly exists: (path: string) => boolean
+  readonly where: (command: "bash") => readonly string[]
+}
+
+export function resolveGitBash(input: GitBashResolverInput): GitBashResolution {
+  if (input.platform !== "win32") return { found: true, path: null, source: "not-required" }
+
+  const checkedPaths: string[] = []
+  const envPath = nonEmptyEnvValue(input.env, GIT_BASH_ENV_KEY)
+  if (envPath !== undefined) {
+    checkedPaths.push(envPath)
+    if (isBashExePath(envPath) && input.exists(envPath)) return { found: true, path: envPath, source: "env" }
+    return missingGitBash(checkedPaths)
+  }
+
+  for (const candidate of [
+    { path: PROGRAM_FILES_GIT_BASH, source: "program-files" },
+    { path: PROGRAM_FILES_X86_GIT_BASH, source: "program-files-x86" },
+  ] as const) {
+    checkedPaths.push(candidate.path)
+    if (input.exists(candidate.path)) return { found: true, path: candidate.path, source: candidate.source }
+  }
+
+  for (const pathCandidate of input.where("bash")) {
+    const candidate = pathCandidate.trim()
+    if (candidate.length === 0) continue
+    checkedPaths.push(candidate)
+    if (isBashExePath(candidate) && input.exists(candidate)) return { found: true, path: candidate, source: "path" }
+  }
+
+  return missingGitBash(checkedPaths)
+}
+
+export function resolveGitBashForCurrentProcess(input: {
+  readonly platform?: string
+  readonly env?: { readonly [key: string]: string | undefined }
+} = {}): GitBashResolution {
+  return resolveGitBash({
+    platform: input.platform ?? process.platform,
+    env: input.env ?? process.env,
+    exists: existsSync,
+    where: whereCommand,
+  })
+}
+
+function missingGitBash(checkedPaths: readonly string[]): GitBashResolution {
+  return {
+    found: false,
+    checkedPaths,
+    installHint: [
+      "Git Bash is required for native Windows Codex profile installs.",
+      "Install it with: winget install --id Git.Git -e --source winget",
+      `For a custom install, set ${GIT_BASH_ENV_KEY}=C:\\path\\to\\bash.exe`,
+      "Then rerun `bunx omo install --platform=codex`.",
+    ].join("\n"),
+  }
+}
+
+function nonEmptyEnvValue(env: { readonly [key: string]: string | undefined }, key: string): string | undefined {
+  const value = env[key]
+  if (value === undefined) return undefined
+  const trimmed = value.trim()
+  return trimmed.length === 0 ? undefined : trimmed
+}
+
+function isBashExePath(path: string): boolean {
+  return path.toLowerCase().endsWith("bash.exe")
+}
+
+function whereCommand(command: "bash"): readonly string[] {
+  try {
+    return execFileSync("where", [command], { encoding: "utf8" })
+      .split(/\r?\n/)
+      .map((line) => line.trim())
+      .filter((line) => line.length > 0)
+  } catch (error) {
+    if (error instanceof Error) return []
+    throw error
+  }
+}