refactor(packages): extract hashline-core package

Move the hash-anchored edit core (hash computation, validation, edit operations, text normalization, chunk formatter, diff utilities, and a runtime-aware xxHash32 binding) into a new @oh-my-opencode/hashline-core workspace package.

The src/tools/hashline-edit/ surface becomes a set of thin re-export shims, so existing import paths in the plugin keep working while the pure logic lives behind a stable package boundary that has no opencode runtime dependencies.

Tests: bun test packages/hashline-core src/tools/hashline-edit

packages/hashline-core/src/edit-deduplication.ts

@@ -0,0 +1,43 @@
+import type { HashlineEdit } from "./types"
+import { toNewLines } from "./edit-text-normalization"
+import { normalizeLineRef } from "./validation"
+
+function normalizeEditPayload(payload: string | string[]): string {
+  return toNewLines(payload).join("\n")
+}
+
+function canonicalAnchor(anchor: string | undefined): string {
+  if (!anchor) return ""
+  return normalizeLineRef(anchor)
+}
+
+function buildDedupeKey(edit: HashlineEdit): string {
+  switch (edit.op) {
+    case "replace":
+      return `replace|${canonicalAnchor(edit.pos)}|${edit.end ? canonicalAnchor(edit.end) : ""}|${normalizeEditPayload(edit.lines)}`
+    case "append":
+      return `append|${canonicalAnchor(edit.pos)}|${normalizeEditPayload(edit.lines)}`
+    case "prepend":
+      return `prepend|${canonicalAnchor(edit.pos)}|${normalizeEditPayload(edit.lines)}`
+    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 }
+}