feat(coder): add hashline editing core + wire audit hooks into dispatch pipeline

Hashline editing: content-hash anchors for edit_file stale-patch detection.
Pure-JS xxHash32, line hash computation, validation with HashlineMismatchError,
256-entry hash dictionary. 6 files in apps/coder/src/services/hashline/.

Audit hooks: emitHook('tool.execute.after') wired in frame-emitter.ts for
completed/failed tool results. emitHook('turn.end') wired at terminal points
in dispatcher.ts (all 5 run functions: native, external, opencode, warm ACP,
claude SDK). Fire-and-forget, non-blocking.

apps/coder/src/services/hashline/hash-computation.ts

@@ -0,0 +1,31 @@
+import { HASHLINE_DICT } from "./constants.js"
+import { hashXxh32 } from "./xxhash32.js"
+
+const RE_SIGNIFICANT = /[\p{L}\p{N}]/u
+
+function computeNormalizedLineHash(lineNumber: number, normalizedContent: string): string {
+  const stripped = normalizedContent
+  const seed = RE_SIGNIFICANT.test(stripped) ? 0 : lineNumber
+  const hash = hashXxh32(stripped, seed)
+  const index = hash % 256
+  return HASHLINE_DICT[index]!
+}
+
+export function computeLineHash(lineNumber: number, content: string): string {
+  return computeNormalizedLineHash(lineNumber, content.replace(/\r/g, "").trimEnd())
+}
+
+export function computeLegacyLineHash(lineNumber: number, content: string): string {
+  return computeNormalizedLineHash(lineNumber, content.replace(/\r/g, "").replace(/\s+/g, ""))
+}
+
+export function formatHashLine(lineNumber: number, content: string): string {
+  const hash = computeLineHash(lineNumber, content)
+  return `${lineNumber}#${hash}|${content}`
+}
+
+export function formatHashLines(content: string): string {
+  if (!content) return ""
+  const lines = content.split("\n")
+  return lines.map((line, index) => formatHashLine(index + 1, line)).join("\n")
+}