diff --git a/packages/opencode/src/flag/flag.ts b/packages/opencode/src/flag/flag.ts
index 2dcf112ae..c4a03e831 100644
--- a/packages/opencode/src/flag/flag.ts
+++ b/packages/opencode/src/flag/flag.ts
@@ -1,5 +1,6 @@
 export namespace Flag {
   export const OPENCODE_AUTO_SHARE = truthy("OPENCODE_AUTO_SHARE")
+  export const OPENCODE_GIT_BASH_PATH = process.env["OPENCODE_GIT_BASH_PATH"]
   export const OPENCODE_CONFIG = process.env["OPENCODE_CONFIG"]
   export const OPENCODE_CONFIG_DIR = process.env["OPENCODE_CONFIG_DIR"]
   export const OPENCODE_CONFIG_CONTENT = process.env["OPENCODE_CONFIG_CONTENT"]
diff --git a/packages/opencode/src/shell/shell.ts b/packages/opencode/src/shell/shell.ts
new file mode 100644
index 000000000..78cd83b66
--- /dev/null
+++ b/packages/opencode/src/shell/shell.ts
@@ -0,0 +1,195 @@
+import { Flag } from "@/flag/flag"
+import { lazy } from "@/util/lazy"
+import { spawn as nodeSpawn } from "child_process"
+import path from "path"
+
+export namespace Shell {
+  const BLACKLIST = new Set(["fish", "nu"])
+  const SIGKILL_TIMEOUT_MS = 200
+
+  function fallback() {
+    if (process.platform === "win32") {
+      if (Flag.OPENCODE_GIT_BASH_PATH) return Flag.OPENCODE_GIT_BASH_PATH
+      const git = Bun.which("git")
+      if (git) {
+        // git.exe is typically at: C:\Program Files\Git\cmd\git.exe
+        // bash.exe is at: C:\Program Files\Git\bin\bash.exe
+        const bash = path.join(git, "..", "..", "bin", "bash.exe")
+        if (Bun.file(bash).size) return bash
+      }
+      return process.env.COMSPEC || "cmd.exe"
+    }
+    if (process.platform === "darwin") return "/bin/zsh"
+    const bash = Bun.which("bash")
+    if (bash) return bash
+    return "/bin/sh"
+  }
+
+  export const preferred = lazy(() => {
+    const s = process.env.SHELL
+    if (s) return s
+    return fallback()
+  })
+
+  export const acceptable = lazy(() => {
+    const s = process.env.SHELL
+    if (s && !BLACKLIST.has(path.basename(s))) return s
+    return fallback()
+  })
+
+  export interface SpawnOptions {
+    command: string
+    cwd: string
+    shell?: string
+    source?: boolean
+    env?: Record<string, string>
+    timeout?: number
+    abort?: AbortSignal
+    onData?: (chunk: Buffer) => void
+  }
+
+  export interface SpawnResult {
+    output: string
+    exitCode: number | null
+    timedOut: boolean
+    aborted: boolean
+  }
+
+  function args(shell: string, command: string, source?: boolean): string[] {
+    const name = path.basename(shell).toLowerCase()
+
+    if (name === "nu") return ["-c", command]
+    if (name === "fish") return ["-c", command]
+
+    if (name === "zsh") {
+      if (!source) return ["-c", command]
+      return [
+        "-c",
+        "-l",
+        `
+          [[ -f ~/.zshenv ]] && source ~/.zshenv >/dev/null 2>&1 || true
+          [[ -f "\${ZDOTDIR:-$HOME}/.zshrc" ]] && source "\${ZDOTDIR:-$HOME}/.zshrc" >/dev/null 2>&1 || true
+          ${command}
+        `.trim(),
+      ]
+    }
+
+    if (name === "bash" || name === "bash.exe") {
+      if (!source) return ["-c", command]
+      return [
+        "-c",
+        "-l",
+        `
+          [[ -f ~/.bashrc ]] && source ~/.bashrc >/dev/null 2>&1 || true
+          ${command}
+        `.trim(),
+      ]
+    }
+
+    if (name === "cmd.exe") return ["/c", command]
+    if (name === "powershell.exe") return ["-NoProfile", "-Command", command]
+
+    // fallback
+    if (!source) return ["-c", command]
+    return ["-c", "-l", command]
+  }
+
+  export async function spawn(options: SpawnOptions): Promise<SpawnResult> {
+    const shell = options.shell ?? acceptable()
+    const proc = nodeSpawn(shell, args(shell, options.command, options.source), {
+      cwd: options.cwd,
+      env: {
+        ...process.env,
+        ...options.env,
+      },
+      stdio: ["ignore", "pipe", "pipe"],
+      detached: process.platform !== "win32",
+    })
+
+    let output = ""
+    let timedOut = false
+    let aborted = false
+    let exited = false
+
+    const append = (chunk: Buffer) => {
+      output += chunk.toString()
+      options.onData?.(chunk)
+    }
+
+    proc.stdout?.on("data", append)
+    proc.stderr?.on("data", append)
+
+    const killTree = async () => {
+      const pid = proc.pid
+      if (!pid || exited) return
+
+      if (process.platform === "win32") {
+        await new Promise<void>((resolve) => {
+          const killer = nodeSpawn("taskkill", ["/pid", String(pid), "/f", "/t"], { stdio: "ignore" })
+          killer.once("exit", resolve)
+          killer.once("error", resolve)
+        })
+        return
+      }
+
+      try {
+        process.kill(-pid, "SIGTERM")
+        await Bun.sleep(SIGKILL_TIMEOUT_MS)
+        if (!exited) {
+          process.kill(-pid, "SIGKILL")
+        }
+      } catch {
+        proc.kill("SIGTERM")
+        await Bun.sleep(SIGKILL_TIMEOUT_MS)
+        if (!exited) {
+          proc.kill("SIGKILL")
+        }
+      }
+    }
+
+    if (options.abort?.aborted) {
+      aborted = true
+      await killTree()
+    }
+
+    const abortHandler = () => {
+      aborted = true
+      void killTree()
+    }
+
+    options.abort?.addEventListener("abort", abortHandler, { once: true })
+
+    const timeoutTimer = options.timeout
+      ? setTimeout(() => {
+          timedOut = true
+          void killTree()
+        }, options.timeout)
+      : undefined
+
+    await new Promise<void>((resolve, reject) => {
+      const cleanup = () => {
+        if (timeoutTimer) clearTimeout(timeoutTimer)
+        options.abort?.removeEventListener("abort", abortHandler)
+      }
+
+      proc.once("exit", () => {
+        exited = true
+        cleanup()
+        resolve()
+      })
+
+      proc.once("error", (error) => {
+        exited = true
+        cleanup()
+        reject(error)
+      })
+    })
+
+    return {
+      output,
+      exitCode: proc.exitCode,
+      timedOut,
+      aborted,
+    }
+  }
+}
diff --git a/packages/opencode/src/tool/bash.ts b/packages/opencode/src/tool/bash.ts
index 0c099fe80..dcfaa6f0d 100644
--- a/packages/opencode/src/tool/bash.ts
+++ b/packages/opencode/src/tool/bash.ts
@@ -14,7 +14,7 @@ import { Permission } from "@/permission"
 import { fileURLToPath } from "url"
 import { Flag } from "@/flag/flag.ts"
 import path from "path"
-import { iife } from "@/util/iife"
+import { Shell } from "@/shell/shell"
 
 const MAX_OUTPUT_LENGTH = Flag.OPENCODE_EXPERIMENTAL_BASH_MAX_OUTPUT_LENGTH || 30_000
 const DEFAULT_TIMEOUT = Flag.OPENCODE_EXPERIMENTAL_BASH_DEFAULT_TIMEOUT_MS || 2 * 60 * 1000
@@ -53,32 +53,7 @@ const parser = lazy(async () => {
 // TODO: we may wanna rename this tool so it works better on other shells
 
 export const BashTool = Tool.define("bash", async () => {
-  const shell = iife(() => {
-    const s = process.env.SHELL
-    if (s) {
-      const basename = path.basename(s)
-      if (!new Set(["fish", "nu"]).has(basename)) {
-        return s
-      }
-    }
-
-    if (process.platform === "darwin") {
-      return "/bin/zsh"
-    }
-
-    if (process.platform === "win32") {
-      // Let Bun / Node pick COMSPEC (usually cmd.exe)
-      // or explicitly:
-      return process.env.COMSPEC || true
-    }
-
-    const bash = Bun.which("bash")
-    if (bash) {
-      return bash
-    }
-
-    return true
-  })
+  const shell = Shell.acceptable()
   log.info("bash tool using shell", { shell })
 
   return {