fix(hashline-edit): widen non-numeric prefix detection and remove duplicate try-catch

- Replace regex /^([A-Za-z_]+)#.../ with indexOf-based prefix check to catch
  line-ref#VK and line.ref#VK style inputs that were previously giving generic errors
- Extract parseLineRefWithHint helper to eliminate duplicated try-catch in
  validateLineRef and validateLineRefs
- Restore idempotency guard in appendWriteHashlineOutput using new output format
- Add tests for LINE42 extraction, line-ref hint, line.ref hint, and guard behavior

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

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

src/hooks/hashline-read-enhancer/index.test.ts

@@ -189,6 +189,28 @@ describe("hashline-read-enhancer", () => {
     fs.rmSync(tempDir, { recursive: true, force: true })
   })
 
+  it("does not re-process write output that already contains the success marker", async () => {
+    //#given
+    const hook = createHashlineReadEnhancerHook(mockCtx(), { hashline_edit: { enabled: true } })
+    const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "hashline-idem-"))
+    const filePath = path.join(tempDir, "demo.ts")
+    fs.writeFileSync(filePath, "a\nb\nc\nd\ne")
+    const input = { tool: "write", sessionID: "s", callID: "c" }
+    const output = {
+      title: "write",
+      output: "File written successfully. 99 lines written.",
+      metadata: { filepath: filePath },
+    }
+
+    //#when
+    await hook["tool.execute.after"](input, output)
+
+    //#then — guard should prevent re-reading the file and updating the count
+    expect(output.output).toBe("File written successfully. 99 lines written.")
+
+    fs.rmSync(tempDir, { recursive: true, force: true })
+  })
+
   it("skips when feature is disabled", async () => {
     //#given
     const hook = createHashlineReadEnhancerHook(mockCtx(), { hashline_edit: { enabled: false } })