feat(shared): add fsync-skip tracker and path-environment classifier

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

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([])
+  })
+})