fix(hashline): accept legacy hashes for indented anchors

Keep persisted LINE#ID anchors working after strict whitespace hashing by falling back to the legacy hash for validation-only lookups.

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

src/tools/hashline-edit/hash-computation.test.ts

@@ -1,6 +1,7 @@
 import { describe, it, expect } from "bun:test"
 import {
   computeLineHash,
+  computeLegacyLineHash,
   formatHashLine,
   formatHashLines,
   streamHashLinesFromLines,
@@ -58,6 +59,19 @@ describe("computeLineHash", () => {
     expect(hash1).not.toBe(hash2)
   })
 
+  it("preserves legacy hashes for leading indentation variants", () => {
+    //#given
+    const content1 = "function hello() {"
+    const content2 = "  function hello() {"
+
+    //#when
+    const hash1 = computeLegacyLineHash(1, content1)
+    const hash2 = computeLegacyLineHash(1, content2)
+
+    //#then
+    expect(hash1).toBe(hash2)
+  })
+
   it("ignores trailing whitespace differences", () => {
     //#given
     const content1 = "function hello() {"

src/tools/hashline-edit/hash-computation.ts

@@ -3,14 +3,22 @@ import { createHashlineChunkFormatter } from "./hashline-chunk-formatter"
 
 const RE_SIGNIFICANT = /[\p{L}\p{N}]/u
 
-export function computeLineHash(lineNumber: number, content: string): string {
-  const stripped = content.replace(/\r/g, "").trimEnd()
+function computeNormalizedLineHash(lineNumber: number, normalizedContent: string): string {
+  const stripped = normalizedContent
   const seed = RE_SIGNIFICANT.test(stripped) ? 0 : lineNumber
   const hash = Bun.hash.xxHash32(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, "").trim())
+}
+
 export function formatHashLine(lineNumber: number, content: string): string {
   const hash = computeLineHash(lineNumber, content)
   return `${lineNumber}#${hash}|${content}`

src/tools/hashline-edit/validation.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from "bun:test"
-import { computeLineHash } from "./hash-computation"
+import { computeLineHash, computeLegacyLineHash } from "./hash-computation"
 import { parseLineRef, validateLineRef, validateLineRefs } from "./validation"
 
 describe("parseLineRef", () => {
@@ -116,6 +116,15 @@ describe("validateLineRef", () => {
     expect(() => validateLineRef(lines, "1#ZZ")).toThrow(/>>>\s+1#[ZPMQVRWSNKTXJBYH]{2}\|/)
   })
 
+  it("accepts legacy hashes for indented lines", () => {
+    //#given
+    const lines = ["  function hello() {", "    return 42", "  }"]
+    const legacyHash = computeLegacyLineHash(1, lines[0])
+
+    //#when / #then
+    expect(() => validateLineRef(lines, `1#${legacyHash}`)).not.toThrow()
+  })
+
   it("shows >>> mismatch context in batched validation", () => {
     //#given
     const lines = ["one", "two", "three", "four"]

src/tools/hashline-edit/validation.ts

@@ -1,4 +1,4 @@
-import { computeLineHash } from "./hash-computation"
+import { computeLegacyLineHash, computeLineHash } from "./hash-computation"
 import { HASHLINE_REF_PATTERN } from "./constants"
 
 export interface LineRef {
@@ -15,6 +15,10 @@ 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
@@ -71,9 +75,7 @@ export function validateLineRef(lines: string[], ref: string): void {
   }
 
   const content = lines[line - 1]
-  const currentHash = computeLineHash(line, content)
-
-  if (currentHash !== hash) {
+  if (!isCompatibleLineHash(line, content, hash)) {
     throw new HashlineMismatchError([{ line, expected: hash }], lines)
   }
 }
@@ -140,8 +142,8 @@ function suggestLineForHash(ref: string, lines: string[]): string | null {
   if (!hashMatch) return null
   const hash = hashMatch[1]
   for (let i = 0; i < lines.length; i++) {
-    if (computeLineHash(i + 1, lines[i]) === hash) {
-      return `Did you mean "${i + 1}#${hash}"?`
+    if (isCompatibleLineHash(i + 1, lines[i], hash)) {
+      return `Did you mean "${i + 1}#${computeLineHash(i + 1, lines[i])}"?`
     }
   }
   return null
@@ -169,8 +171,7 @@ export function validateLineRefs(lines: string[], refs: string[]): void {
     }
 
     const content = lines[line - 1]
-    const currentHash = computeLineHash(line, content)
-    if (currentHash !== hash) {
+    if (!isCompatibleLineHash(line, content, hash)) {
       mismatches.push({ line, expected: hash })
     }
   }