diff --git a/src/hooks/write-existing-file-guard/index.test.ts b/src/hooks/write-existing-file-guard/index.test.ts
index d1d222788..588c083fc 100644
--- a/src/hooks/write-existing-file-guard/index.test.ts
+++ b/src/hooks/write-existing-file-guard/index.test.ts
@@ -4,6 +4,7 @@ import { tmpdir } from "node:os"
 import { dirname, join, resolve } from "node:path"
 
 import { createWriteExistingFileGuardHook } from "./index"
+import { isOmoWorkspacePath } from "./tool-execute-before-handler"
 
 const BLOCK_MESSAGE = "File already exists. Use edit tool instead."
 
@@ -255,6 +256,14 @@ describe("createWriteExistingFileGuardHook", () => {
     ).resolves.toBeDefined()
   })
 
+  test("#given canonical paths #when checking .omo workspace segment #then supports Windows separators", () => {
+    expect(isOmoWorkspacePath(".omo/plans/plan.txt")).toBe(true)
+    expect(isOmoWorkspacePath("/repo/.omo/plans/plan.txt")).toBe(true)
+    expect(isOmoWorkspacePath(String.raw`C:\repo\.omo\plans\plan.txt`)).toBe(true)
+    expect(isOmoWorkspacePath("/repo/work.omo/plans/plan.txt")).toBe(false)
+    expect(isOmoWorkspacePath(String.raw`C:\repo\.omo-backup\plans\plan.txt`)).toBe(false)
+  })
+
   test("#given file arg variants #when read then write executes #then supports all variants", async () => {
     const existingFile = createFile("variants.txt")
     const variants: Array<"filePath" | "path" | "file_path"> = [
diff --git a/src/hooks/write-existing-file-guard/tool-execute-before-handler.ts b/src/hooks/write-existing-file-guard/tool-execute-before-handler.ts
index db2ade562..09f094948 100644
--- a/src/hooks/write-existing-file-guard/tool-execute-before-handler.ts
+++ b/src/hooks/write-existing-file-guard/tool-execute-before-handler.ts
@@ -85,6 +85,10 @@ function invalidateOtherSessions(
   }
 }
 
+export function isOmoWorkspacePath(canonicalPath: string): boolean {
+  return /(^|[/\\])\.omo([/\\]|$)/.test(canonicalPath)
+}
+
 export async function handleWriteExistingFileGuardToolExecuteBefore(params: {
   ctx: PluginInput
   input: { tool?: string; sessionID?: string }
@@ -149,8 +153,7 @@ export async function handleWriteExistingFileGuardToolExecuteBefore(params: {
     return
   }
 
-  const isOmoPath = canonicalPath.includes("/.omo/")
-  if (isOmoPath) {
+  if (isOmoWorkspacePath(canonicalPath)) {
     log("[write-existing-file-guard] Allowing .omo/** overwrite", {
       sessionID: input.sessionID,
       filePath,