feat(hooks): surface fsync-skip warnings to AI agent via tool output

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

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

src/shared/fsync-skip-warning-formatter.ts

@@ -0,0 +1,61 @@
+import { describePathClassification } from "./classify-path-environment"
+import type { FsyncSkipEntry } from "./fsync-skip-tracker"
+
+const MAX_PATH_LINES = 5
+
+function selectMostCommonClassification(
+  entries: FsyncSkipEntry[],
+): FsyncSkipEntry["pathClassification"] {
+  const counts = new Map<FsyncSkipEntry["pathClassification"], number>()
+
+  for (const entry of entries) {
+    const currentCount = counts.get(entry.pathClassification) ?? 0
+    counts.set(entry.pathClassification, currentCount + 1)
+  }
+
+  let selected: FsyncSkipEntry["pathClassification"] = "unknown"
+  let selectedCount = -1
+  for (const [classification, count] of counts.entries()) {
+    if (count > selectedCount) {
+      selected = classification
+      selectedCount = count
+    }
+  }
+
+  return selected
+}
+
+export function formatFsyncSkipWarning(entries: FsyncSkipEntry[]): string {
+  if (entries.length === 0) return ""
+
+  const selectedClassification = selectMostCommonClassification(entries)
+  const selectedDescription = describePathClassification(selectedClassification)
+  const shownEntries = entries.slice(0, MAX_PATH_LINES)
+  const hiddenCount = Math.max(entries.length - shownEntries.length, 0)
+  const pathLines = shownEntries.map((entry) => `  - ${entry.filePath} (code: ${entry.errorCode})`)
+  if (hiddenCount > 0) {
+    pathLines.push(`  ... and ${hiddenCount} more`)
+  }
+
+  const environmentLines = selectedClassification === "unknown"
+    ? []
+    : [`Detected environment: ${selectedDescription}`]
+
+  const durabilityLine = selectedClassification === "unknown"
+    ? "  - Crash durability is best-effort because this filesystem does not support fsync."
+    : "  - Crash durability is best-effort on this filesystem (this is normal for iCloud, OneDrive, network drives, antivirus-locked paths)."
+
+  return [
+    "---",
+    `[fsync-skipped] ${entries.length} write(s) bypassed fsync because the underlying filesystem rejected the syscall.`,
+    "",
+    ...environmentLines,
+    "Affected paths:",
+    ...pathLines,
+    "",
+    "What this means:",
+    "  - The write+rename succeeded — the file is on disk, atomicity is preserved.",
+    durabilityLine,
+    "  - No action required. Operation completed successfully.",
+  ].join("\n")
+}