From ab768029fa3c147d3ae9266d8c818264ce5ebcaa Mon Sep 17 00:00:00 2001
From: YeonGyu-Kim <code.yeon.gyu@gmail.com>
Date: Mon, 23 Feb 2026 18:51:25 +0900
Subject: [PATCH] refactor(hashline-edit): stabilize hashes and tighten prefix
 stripping

Switch line hashing to significance-aware seeding so meaningful lines stay stable across reflows while punctuation-only lines still disambiguate by line index.

Also narrow prefix stripping to hashline/diff patterns that reduce accidental content corruption during edit normalization.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
---
 src/tools/hashline-edit/edit-text-normalization.ts |  4 ++--
 src/tools/hashline-edit/hash-computation.test.ts   | 14 +++++++++++++-
 src/tools/hashline-edit/hash-computation.ts        |  8 +++++---
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/tools/hashline-edit/edit-text-normalization.ts b/src/tools/hashline-edit/edit-text-normalization.ts
index b508bf57..beb6ac87 100644
--- a/src/tools/hashline-edit/edit-text-normalization.ts
+++ b/src/tools/hashline-edit/edit-text-normalization.ts
@@ -1,5 +1,5 @@
-const HASHLINE_PREFIX_RE = /^\s*(?:>>>|>>)?\s*\d+#[A-Z]{2}:/
-const DIFF_PLUS_RE = /^[+-](?![+-])/
+const HASHLINE_PREFIX_RE = /^\s*(?:>>>|>>)?\s*\d+\s*#\s*[ZPMQVRWSNKTXJBYH]{2}:/
+const DIFF_PLUS_RE = /^[+](?![+])/
 
 function equalsIgnoringWhitespace(a: string, b: string): boolean {
   if (a === b) return true
diff --git a/src/tools/hashline-edit/hash-computation.test.ts b/src/tools/hashline-edit/hash-computation.test.ts
index bbca1baa..d73a2db2 100644
--- a/src/tools/hashline-edit/hash-computation.test.ts
+++ b/src/tools/hashline-edit/hash-computation.test.ts
@@ -21,7 +21,7 @@ describe("computeLineHash", () => {
     expect(hash1).toMatch(/^[ZPMQVRWSNKTXJBYH]{2}$/)
   })
 
-  it("produces different hashes for same content on different lines", () => {
+  it("produces same hashes for significant content on different lines", () => {
     //#given
     const content = "function hello() {"
 
@@ -29,6 +29,18 @@ describe("computeLineHash", () => {
     const hash1 = computeLineHash(1, content)
     const hash2 = computeLineHash(2, content)
 
+    //#then
+    expect(hash1).toBe(hash2)
+  })
+
+  it("mixes line number for non-significant lines", () => {
+    //#given
+    const punctuationOnly = "{}"
+
+    //#when
+    const hash1 = computeLineHash(1, punctuationOnly)
+    const hash2 = computeLineHash(2, punctuationOnly)
+
     //#then
     expect(hash1).not.toBe(hash2)
   })
diff --git a/src/tools/hashline-edit/hash-computation.ts b/src/tools/hashline-edit/hash-computation.ts
index 374bd56d..8371887d 100644
--- a/src/tools/hashline-edit/hash-computation.ts
+++ b/src/tools/hashline-edit/hash-computation.ts
@@ -1,10 +1,12 @@
 import { HASHLINE_DICT } from "./constants"
 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(/\s+/g, "")
-  const hashInput = `${lineNumber}:${stripped}`
-  const hash = Bun.hash.xxHash32(hashInput)
+  const stripped = content.endsWith("\r") ? content.slice(0, -1).replace(/\s+/g, "") : content.replace(/\s+/g, "")
+  const seed = RE_SIGNIFICANT.test(stripped) ? 0 : lineNumber
+  const hash = Bun.hash.xxHash32(stripped, seed)
   const index = hash % 256
   return HASHLINE_DICT[index]
 }