diff --git a/src/shared/classify-path-environment.test.ts b/src/shared/classify-path-environment.test.ts
new file mode 100644
index 000000000..0fc45c4b7
--- /dev/null
+++ b/src/shared/classify-path-environment.test.ts
@@ -0,0 +1,56 @@
+import { describe, expect, it } from "bun:test"
+
+import {
+  classifyPathEnvironment,
+  describePathClassification,
+} from "./classify-path-environment"
+
+describe("classifyPathEnvironment", () => {
+  it("classifies macOS iCloud path as icloud", () => {
+    expect(
+      classifyPathEnvironment(
+        "/Users/x/Library/Mobile Documents/com~apple~CloudDocs/project/file.txt",
+      ),
+    ).toBe("icloud")
+  })
+
+  it("classifies OneDrive path on unix style", () => {
+    expect(classifyPathEnvironment("/Users/x/OneDrive/foo")).toBe("onedrive")
+  })
+
+  it("classifies OneDrive path on windows style", () => {
+    expect(classifyPathEnvironment("C:\\Users\\x\\OneDrive\\foo")).toBe("onedrive")
+  })
+
+  it("classifies macOS Desktop path as desktop-sync", () => {
+    expect(classifyPathEnvironment("/Users/x/Desktop/foo")).toBe("desktop-sync")
+  })
+
+  it("classifies /Volumes path as network-drive", () => {
+    expect(classifyPathEnvironment("/Volumes/NetworkShare/foo")).toBe("network-drive")
+  })
+
+  it("classifies random path as unknown", () => {
+    expect(classifyPathEnvironment("/tmp/foo")).toBe("unknown")
+  })
+
+  it("classifies empty string as unknown", () => {
+    expect(classifyPathEnvironment("")).toBe("unknown")
+  })
+
+  it("matches OneDrive case-insensitively", () => {
+    expect(classifyPathEnvironment("/Users/x/oNeDrIvE/foo")).toBe("onedrive")
+  })
+})
+
+describe("describePathClassification", () => {
+  it("returns human-readable descriptions", () => {
+    expect(describePathClassification("icloud")).toBe("iCloud Drive")
+    expect(describePathClassification("onedrive")).toBe("OneDrive")
+    expect(describePathClassification("desktop-sync")).toBe("Desktop sync (macOS)")
+    expect(describePathClassification("network-drive")).toBe("Network drive")
+    expect(describePathClassification("unknown")).toBe(
+      "filesystem that does not support fsync",
+    )
+  })
+})
diff --git a/src/shared/classify-path-environment.ts b/src/shared/classify-path-environment.ts
new file mode 100644
index 000000000..fe2974d54
--- /dev/null
+++ b/src/shared/classify-path-environment.ts
@@ -0,0 +1,68 @@
+import { homedir } from "node:os"
+import path from "node:path"
+
+export type PathClassification =
+  | "icloud"
+  | "onedrive"
+  | "desktop-sync"
+  | "network-drive"
+  | "unknown"
+
+function normalizeInputPath(absolutePath: string): string {
+  return absolutePath.replaceAll("\\", "/")
+}
+
+function isUnderPath(normalizedPath: string, normalizedParentPath: string): boolean {
+  return normalizedPath === normalizedParentPath || normalizedPath.startsWith(`${normalizedParentPath}/`)
+}
+
+export function classifyPathEnvironment(absolutePath: string): PathClassification {
+  if (absolutePath.length === 0) return "unknown"
+
+  const normalizedPath = normalizeInputPath(absolutePath)
+  const lowercasePath = normalizedPath.toLowerCase()
+  if (lowercasePath.includes("/onedrive") || lowercasePath.includes("/onedrive/")) {
+    return "onedrive"
+  }
+
+  if (normalizedPath.includes("/Library/Mobile Documents/")) {
+    return "icloud"
+  }
+
+  if (isUnderPath(normalizedPath, "/Volumes")) {
+    return "network-drive"
+  }
+
+  if (
+    normalizedPath.startsWith("/Users/")
+    && (normalizedPath.includes("/Desktop/") || normalizedPath.endsWith("/Desktop")
+      || normalizedPath.includes("/Documents/") || normalizedPath.endsWith("/Documents"))
+  ) {
+    return "desktop-sync"
+  }
+
+  const normalizedHome = normalizeInputPath(homedir())
+  const desktopPath = normalizeInputPath(path.join(normalizedHome, "Desktop"))
+  const documentsPath = normalizeInputPath(path.join(normalizedHome, "Documents"))
+
+  if (isUnderPath(normalizedPath, desktopPath) || isUnderPath(normalizedPath, documentsPath)) {
+    return "desktop-sync"
+  }
+
+  return "unknown"
+}
+
+export function describePathClassification(pathClassification: PathClassification): string {
+  switch (pathClassification) {
+    case "icloud":
+      return "iCloud Drive"
+    case "onedrive":
+      return "OneDrive"
+    case "desktop-sync":
+      return "Desktop sync (macOS)"
+    case "network-drive":
+      return "Network drive"
+    case "unknown":
+      return "filesystem that does not support fsync"
+  }
+}
diff --git a/src/shared/fsync-skip-tracker.test.ts b/src/shared/fsync-skip-tracker.test.ts
new file mode 100644
index 000000000..897e5efe8
--- /dev/null
+++ b/src/shared/fsync-skip-tracker.test.ts
@@ -0,0 +1,100 @@
+import { beforeEach, describe, expect, it } from "bun:test"
+
+import {
+  clearAllSkips,
+  drainSkipsAfter,
+  recordFsyncSkip,
+} from "./fsync-skip-tracker"
+
+type PathClassification =
+  | "icloud"
+  | "onedrive"
+  | "desktop-sync"
+  | "network-drive"
+  | "unknown"
+
+function recordSkip(index: number, pathClassification: PathClassification = "unknown"): void {
+  recordFsyncSkip({
+    filePath: `/tmp/file-${index}.txt`,
+    contextLabel: `atomicWrite:/tmp/file-${index}.txt`,
+    errorCode: "EPERM",
+    message: "operation not permitted",
+    pathClassification,
+  })
+}
+
+describe("fsync-skip-tracker", () => {
+  beforeEach(() => {
+    clearAllSkips()
+  })
+
+  it("recordFsyncSkip adds entry with timestamp", () => {
+    const before = Date.now()
+    recordSkip(1)
+    const entries = drainSkipsAfter(0)
+
+    expect(entries).toHaveLength(1)
+    expect(entries[0]?.filePath).toBe("/tmp/file-1.txt")
+    expect(entries[0]?.timestamp).toBeGreaterThanOrEqual(before)
+  })
+
+  it("drainSkipsAfter(timestamp) returns entries strictly after the timestamp", async () => {
+    recordSkip(1)
+    const firstTimestamp = Date.now()
+
+    await Bun.sleep(2)
+
+    recordSkip(2)
+    const drained = drainSkipsAfter(firstTimestamp)
+    expect(drained).toHaveLength(1)
+    expect(drained[0]?.filePath).toBe("/tmp/file-2.txt")
+  })
+
+  it("drainSkipsAfter removes drained entries from buffer", () => {
+    recordSkip(1)
+    recordSkip(2)
+
+    const drained = drainSkipsAfter(0)
+    expect(drained).toHaveLength(2)
+    expect(drainSkipsAfter(0)).toEqual([])
+  })
+
+  it("buffer is bounded to max 200 entries and drops oldest on overflow", () => {
+    for (let index = 1; index <= 205; index += 1) {
+      recordSkip(index)
+    }
+
+    const drained = drainSkipsAfter(0)
+    expect(drained).toHaveLength(200)
+    expect(drained[0]?.filePath).toBe("/tmp/file-6.txt")
+    expect(drained[199]?.filePath).toBe("/tmp/file-205.txt")
+  })
+
+  it("multiple records with same path are kept", () => {
+    recordSkip(1)
+    recordFsyncSkip({
+      filePath: "/tmp/file-1.txt",
+      contextLabel: "acquireLock:/tmp/file-1.txt",
+      errorCode: "EPERM",
+      message: "second",
+      pathClassification: "unknown",
+    })
+
+    const drained = drainSkipsAfter(0)
+    expect(drained).toHaveLength(2)
+    expect(drained[0]?.filePath).toBe("/tmp/file-1.txt")
+    expect(drained[1]?.filePath).toBe("/tmp/file-1.txt")
+  })
+
+  it("drainSkipsAfter(0) returns all entries", () => {
+    recordSkip(1)
+    recordSkip(2)
+
+    const drained = drainSkipsAfter(0)
+    expect(drained).toHaveLength(2)
+  })
+
+  it("empty buffer returns empty array", () => {
+    expect(drainSkipsAfter(0)).toEqual([])
+  })
+})
diff --git a/src/shared/fsync-skip-tracker.ts b/src/shared/fsync-skip-tracker.ts
new file mode 100644
index 000000000..3ee7a7125
--- /dev/null
+++ b/src/shared/fsync-skip-tracker.ts
@@ -0,0 +1,42 @@
+import type { PathClassification } from "./classify-path-environment"
+
+export type FsyncSkipEntry = {
+  filePath: string
+  contextLabel: string
+  errorCode: string
+  message: string
+  pathClassification: PathClassification
+  timestamp: number
+}
+
+const MAX_SKIPS = 200
+const fsyncSkips: FsyncSkipEntry[] = []
+
+export function recordFsyncSkip(entry: Omit<FsyncSkipEntry, "timestamp">): void {
+  fsyncSkips.push({ ...entry, timestamp: Date.now() })
+
+  if (fsyncSkips.length > MAX_SKIPS) {
+    fsyncSkips.splice(0, fsyncSkips.length - MAX_SKIPS)
+  }
+}
+
+export function drainSkipsAfter(timestampMs: number): FsyncSkipEntry[] {
+  const drainedEntries: FsyncSkipEntry[] = []
+  const retainedEntries: FsyncSkipEntry[] = []
+
+  for (const entry of fsyncSkips) {
+    if (entry.timestamp > timestampMs) {
+      drainedEntries.push(entry)
+      continue
+    }
+
+    retainedEntries.push(entry)
+  }
+
+  fsyncSkips.splice(0, fsyncSkips.length, ...retainedEntries)
+  return drainedEntries
+}
+
+export function clearAllSkips(): void {
+  fsyncSkips.length = 0
+}