Oh My Pi: Hashline Editing In A General-Purpose Agent

Why It Matters

A lot of coding agents improve edits by piling on more fuzzy matching. Oh My Pi goes in a different direction. It changes the address space. The model does not primarily say "replace this literal block." It points at anchored lines that were already shown by the read tool.

That changes both cost and failure behavior. The model spends fewer tokens repeating code, and the runtime can distinguish between stale anchors, malformed edit syntax, and true semantic mistakes instead of collapsing everything into "search string not found."

The Anchor Format

In packages/coding-agent/src/edit/line-hash.ts, each visible source line is rendered as LINE+HASH|TEXT. The hash is only two letters long, but it is chosen from a stable set of 647 single-token BPE bigrams so the anchor stays compact in model context.

The details are more careful than they first look. Lines with real alphanumeric content hash independently of the line number so the same content can survive small shifts. Punctuation-only lines can mix in the line number to avoid a sea of identical anchors.

export function computeLineHash(idx: number, line: string): string {
  line = line.replace(/\r/g, "").trimEnd();
  if (line.replace(/[\s{}]/g, "").length === 0) {
    return structuralBigram(idx);
  }
  const seed = /[\p{L}\p{N}]/u.test(line) ? 0 : idx;
  return HL_BIGRAMS[Bun.hash.xxHash32(line, seed) % HL_BIGRAMS_COUNT];
}

Hashline Is The Default, Not An Experiment

This is not a side tool hidden behind a flag. In src/utils/edit-mode.ts, the default edit mode is hashline. In the settings schema, readHashLines is enabled by default, which means the normal read path already formats file output for hashline edits.

How A Hashline Edit Executes

The execution path in src/edit/modes/hashline.ts is where the design becomes interesting. Multi-section edits are split by @PATH, same-path sections are merged so earlier sub-edits do not invalidate later anchors, and multi-file batches are validated before any partial mutation lands.

The runtime then applies edits against normalized file content, restores the original line endings and BOM, emits a compact diff preview, and can auto-rebase a stale anchor within a small search window when the same hash uniquely appears nearby.

if (sections.length === 1) return executeHashlineSection(...);

for (const section of sections) await preflightHashlineSection(...);

for (const section of sections) {
  results.push({ path: section.path, result: await executeHashlineSection(...) });
}

Compare It To The Rest

The key distinction is this: Dirac feels like a deliberate alternative to line-number editing itself. Oh My Pi feels like a broad agent that decided its default edit dialect should be anchor-first, while still keeping replace, patch, vim, and apply_patch as other edit modes.

Why The Repo Is Worth Studying

The editing story is stronger because the repo supports it everywhere else. There are prompt helpers that compute real anchors, settings and previews shaped around hashline, a dedicated typescript-edit-benchmark package, and benchmark scripts specifically for the hashline variant. That is a much more serious loop than dropping a new edit syntax into a prompt and hoping it wins.

In other words, Oh My Pi is not interesting because hashes are cool. It is interesting because the team keeps tuning the whole surrounding system until the hashes actually help.

What I Would Steal From It