feat(hashline-edit): add autocorrect, BOM/CRLF normalization, and file creation support

Implements key features from oh-my-pi to improve agent editing success rates:

- Autocorrect v1: single-line merge expansion, wrapped line restoration,
  paired indent restoration (autocorrect-replacement-lines.ts)
- BOM/CRLF normalization: canonicalize on read, restore on write
  (file-text-canonicalization.ts)
- Pre-validate all hashes before mutation (edit-ordering.ts)
- File creation via append/prepend operations (new types + executor logic)
- Modular refactoring: split edit-operations.ts into focused modules
  (primitives, ordering, deduplication, diff, executor)
- Enhanced tool description with operation choice guide and recovery hints

All 50 tests pass. TypeScript clean. Build successful.

src/tools/hashline-edit/edit-deduplication.ts

@@ -0,0 +1,47 @@
+import type { HashlineEdit } from "./types"
+import { toNewLines } from "./edit-text-normalization"
+
+function normalizeEditPayload(payload: string | string[]): string {
+  return toNewLines(payload).join("\n")
+}
+
+function buildDedupeKey(edit: HashlineEdit): string {
+  switch (edit.type) {
+    case "set_line":
+      return `set_line|${edit.line}|${normalizeEditPayload(edit.text)}`
+    case "replace_lines":
+      return `replace_lines|${edit.start_line}|${edit.end_line}|${normalizeEditPayload(edit.text)}`
+    case "insert_after":
+      return `insert_after|${edit.line}|${normalizeEditPayload(edit.text)}`
+    case "insert_before":
+      return `insert_before|${edit.line}|${normalizeEditPayload(edit.text)}`
+    case "insert_between":
+      return `insert_between|${edit.after_line}|${edit.before_line}|${normalizeEditPayload(edit.text)}`
+    case "replace":
+      return `replace|${edit.old_text}|${normalizeEditPayload(edit.new_text)}`
+    case "append":
+      return `append|${normalizeEditPayload(edit.text)}`
+    case "prepend":
+      return `prepend|${normalizeEditPayload(edit.text)}`
+    default:
+      return JSON.stringify(edit)
+  }
+}
+
+export function dedupeEdits(edits: HashlineEdit[]): { edits: HashlineEdit[]; deduplicatedEdits: number } {
+  const seen = new Set<string>()
+  const deduped: HashlineEdit[] = []
+  let deduplicatedEdits = 0
+
+  for (const edit of edits) {
+    const key = buildDedupeKey(edit)
+    if (seen.has(key)) {
+      deduplicatedEdits += 1
+      continue
+    }
+    seen.add(key)
+    deduped.push(edit)
+  }
+
+  return { edits: deduped, deduplicatedEdits }
+}