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/validation.ts

@@ -0,0 +1,192 @@
+import { computeLegacyLineHash, computeLineHash } from "./hash-computation.js"
+import { HASHLINE_REF_PATTERN } from "./constants.js"
+
+export interface LineRef {
+  line: number
+  hash: string
+}
+
+interface HashMismatch {
+  line: number
+  expected: string
+}
+
+const MISMATCH_CONTEXT = 2
+
+const LINE_REF_EXTRACT_PATTERN = /([0-9]+#[ZPMQVRWSNKTXJBYH]{2})/
+
+function isCompatibleLineHash(line: number, content: string, hash: string): boolean {
+  return computeLineHash(line, content) === hash || computeLegacyLineHash(line, content) === hash
+}
+
+export function normalizeLineRef(ref: string): string {
+  const originalTrimmed = ref.trim()
+  let trimmed = originalTrimmed
+  trimmed = trimmed.replace(/^(?:>>>|[+-])\s*/, "")
+  trimmed = trimmed.replace(/\s*#\s*/, "#")
+  trimmed = trimmed.replace(/\|.*$/, "")
+  trimmed = trimmed.trim()
+
+  if (HASHLINE_REF_PATTERN.test(trimmed)) {
+    return trimmed
+  }
+
+  const extracted = trimmed.match(LINE_REF_EXTRACT_PATTERN)
+  if (extracted) {
+    return extracted[1]!
+  }
+
+  return originalTrimmed
+}
+
+export function parseLineRef(ref: string): LineRef {
+  const normalized = normalizeLineRef(ref)
+  const match = normalized.match(HASHLINE_REF_PATTERN)
+  if (match) {
+    return {
+      line: Number.parseInt(match[1]!, 10),
+      hash: match[2]!,
+    }
+  }
+  const hashIdx = normalized.indexOf('#')
+  if (hashIdx > 0) {
+    const prefix = normalized.slice(0, hashIdx)
+    const suffix = normalized.slice(hashIdx + 1)
+    if (!/^\d+$/.test(prefix) && /^[ZPMQVRWSNKTXJBYH]{2}$/.test(suffix)) {
+      throw new Error(
+        `Invalid line reference: "${ref}". "${prefix}" is not a line number. ` +
+          `Use the actual line number from the read output.`
+      )
+    }
+  }
+  throw new Error(
+    `Invalid line reference format: "${ref}". Expected format: "{line_number}#{hash_id}"`
+  )
+}
+
+export function validateLineRef(lines: string[], ref: string): void {
+  const { line, hash } = parseLineRefWithHint(ref, lines)
+
+  if (line < 1 || line > lines.length) {
+    throw new Error(
+      `Line number ${line} out of bounds. File has ${lines.length} lines.`
+    )
+  }
+
+  const content = lines[line - 1]
+  if (content === undefined) {
+    throw new Error(
+      `Line number ${line} out of bounds. File has ${lines.length} lines.`
+    )
+  }
+  if (!isCompatibleLineHash(line, content, hash)) {
+    throw new HashlineMismatchError([{ line, expected: hash }], lines)
+  }
+}
+
+export class HashlineMismatchError extends Error {
+  readonly remaps: ReadonlyMap<string, string>
+
+  constructor(
+    private readonly mismatches: HashMismatch[],
+    private readonly fileLines: string[]
+  ) {
+    super(HashlineMismatchError.formatMessage(mismatches, fileLines))
+    this.name = "HashlineMismatchError"
+    const remaps = new Map<string, string>()
+    for (const mismatch of mismatches) {
+      const content = fileLines[mismatch.line - 1]
+      const actualLine = content ?? ""
+      const actual = computeLineHash(mismatch.line, actualLine)
+      remaps.set(`${mismatch.line}#${mismatch.expected}`, `${mismatch.line}#${actual}`)
+    }
+    this.remaps = remaps
+  }
+
+  static formatMessage(mismatches: HashMismatch[], fileLines: string[]): string {
+    const mismatchByLine = new Map<number, HashMismatch>()
+    for (const mismatch of mismatches) mismatchByLine.set(mismatch.line, mismatch)
+
+    const displayLines = new Set<number>()
+    for (const mismatch of mismatches) {
+      const low = Math.max(1, mismatch.line - MISMATCH_CONTEXT)
+      const high = Math.min(fileLines.length, mismatch.line + MISMATCH_CONTEXT)
+      for (let line = low; line <= high; line++) displayLines.add(line)
+    }
+
+    const sortedLines = [...displayLines].sort((a, b) => a - b)
+    const output: string[] = []
+    output.push(
+      `${mismatches.length} line${mismatches.length > 1 ? "s have" : " has"} changed since last read. ` +
+        "Use updated {line_number}#{hash_id} references below (>>> marks changed lines)."
+    )
+    output.push("")
+
+    let previousLine = -1
+    for (const line of sortedLines) {
+      if (previousLine !== -1 && line > previousLine + 1) {
+        output.push("    ...")
+      }
+      previousLine = line
+
+      const content = fileLines[line - 1] ?? ""
+      const hash = computeLineHash(line, content)
+      const prefix = `${line}#${hash}|${content}`
+      if (mismatchByLine.has(line)) {
+        output.push(`>>> ${prefix}`)
+      } else {
+        output.push(`    ${prefix}`)
+      }
+    }
+
+    return output.join("\n")
+  }
+}
+
+function suggestLineForHash(ref: string, lines: string[]): string | null {
+  const hashMatch = ref.trim().match(/#([ZPMQVRWSNKTXJBYH]{2})$/)
+  if (!hashMatch) return null
+  const hash = hashMatch[1]!
+  for (let i = 0; i < lines.length; i++) {
+    if (isCompatibleLineHash(i + 1, lines[i] ?? "", hash)) {
+      return `Did you mean "${i + 1}#${computeLineHash(i + 1, lines[i] ?? "")}"?`
+    }
+  }
+  return null
+}
+
+function parseLineRefWithHint(ref: string, lines: string[]): LineRef {
+  try {
+    return parseLineRef(ref)
+  } catch (parseError) {
+    const hint = suggestLineForHash(ref, lines)
+    if (hint && parseError instanceof Error) {
+      throw new Error(`${parseError.message} ${hint}`)
+    }
+    throw parseError
+  }
+}
+
+export function validateLineRefs(lines: string[], refs: string[]): void {
+  const mismatches: HashMismatch[] = []
+
+  for (const ref of refs) {
+    const { line, hash } = parseLineRefWithHint(ref, lines)
+
+    if (line < 1 || line > lines.length) {
+      throw new Error(`Line number ${line} out of bounds (file has ${lines.length} lines)`)
+    }
+
+    const content = lines[line - 1]
+    if (content === undefined) {
+      throw new Error(`Line number ${line} out of bounds (file has ${lines.length} lines)`)
+    }
+    if (!isCompatibleLineHash(line, content, hash)) {
+      mismatches.push({ line, expected: hash })
+    }
+  }
+
+  if (mismatches.length > 0) {
+    throw new HashlineMismatchError(mismatches, lines)
+  }
+}