bot/extensions/diffs

@hanzo/bot-diffs

Read-only diff viewer plugin for Hanzo Bot agents.

It gives agents one tool, diffs, that can:

• render a gateway-hosted diff viewer for canvas use
• render the same diff to a file (PNG or PDF)
• accept either arbitrary before and after text or a unified patch

What Agents Get

The tool can return:

• details.viewerUrl: a gateway URL that can be opened in the canvas
• details.filePath: a local rendered artifact path when file rendering is requested
• details.fileFormat: the rendered file format (png or pdf)

When the plugin is enabled, it also ships a companion skill from skills/ and prepends stable tool-usage guidance into system-prompt space via before_prompt_build. The hook uses prependSystemContext, so the guidance stays out of user-prompt space while still being available every turn.

This means an agent can:

• call diffs with mode=view, then pass details.viewerUrl to canvas present
• call diffs with mode=file, then send the file through the normal message tool using path or filePath
• call diffs with mode=both when it wants both outputs

Tool Inputs

Before and after:

{
  "before": "# Hello\n\nOne",
  "after": "# Hello\n\nTwo",
  "path": "docs/example.md",
  "mode": "view"
}

Patch:

{
  "patch": "diff --git a/src/example.ts b/src/example.ts\n--- a/src/example.ts\n+++ b/src/example.ts\n@@ -1 +1 @@\n-const x = 1;\n+const x = 2;\n",
  "mode": "both"
}

Useful options:

• mode: view, file, or both
• layout: unified or split
• theme: light or dark (default: dark)
• fileFormat: png or pdf (default: png)
• fileQuality: standard, hq, or print
• fileScale: device scale override (1-4)
• fileMaxWidth: max width override in CSS pixels (640-2400)
• expandUnchanged: expand unchanged sections (per-call option only, not a plugin default key)
• path: display name for before and after input
• title: explicit viewer title
• ttlSeconds: artifact lifetime
• baseUrl: override the gateway base URL used in the returned viewer link (origin or origin+base path only; no query/hash)

Input safety limits:

• before and after: max 512 KiB each
• patch: max 2 MiB
• patch rendering cap: max 128 files / 120,000 lines

Plugin Defaults

Set plugin-wide defaults in ~/.hanzoai/bot.json:

{
  plugins: {
    entries: {
      diffs: {
        enabled: true,
        config: {
          defaults: {
            fontFamily: "Fira Code",
            fontSize: 15,
            lineSpacing: 1.6,
            layout: "unified",
            showLineNumbers: true,
            diffIndicators: "bars",
            wordWrap: true,
            background: true,
            theme: "dark",
            fileFormat: "png",
            fileQuality: "standard",
            fileScale: 2,
            fileMaxWidth: 960,
            mode: "both",
          },
        },
      },
    },
  },
}

Explicit tool parameters still win over these defaults.

Security options:

• security.allowRemoteViewer (default false): allows non-loopback access to /plugins/diffs/view/... token URLs

Example Agent Prompts

Open in canvas:

Use the `diffs` tool in `view` mode for this before and after content, then open the returned viewer URL in the canvas.

Path: docs/example.md

Before:
# Hello

This is version one.

After:
# Hello

This is version two.

Render a file (PNG or PDF):

Use the `diffs` tool in `file` mode for this before and after input. After it returns `details.filePath`, use the `message` tool with `path` or `filePath` to send me the rendered diff file.

Path: README.md

Before:
Hanzo Bot supports plugins.

After:
Hanzo Bot supports plugins and hosted diff views.

Do both:

Use the `diffs` tool in `both` mode for this diff. Open the viewer in the canvas and then send the rendered file by passing `details.filePath` to the `message` tool.

Path: src/demo.ts

Before:
const status = "old";

After:
const status = "new";

Patch input:

Use the `diffs` tool with this unified patch in `view` mode. After it returns the viewer URL, present it in the canvas.

diff --git a/src/example.ts b/src/example.ts
--- a/src/example.ts
+++ b/src/example.ts
@@ -1,3 +1,3 @@
 export function add(a: number, b: number) {
-  return a + b;
+  return a + b + 1;
 }

Notes

• The viewer is hosted locally through the gateway under /plugins/diffs/....
• Artifacts are ephemeral and stored in the plugin temp subfolder ($TMPDIR/hanzo-bot-diffs).
• Default viewer URLs use loopback (127.0.0.1) unless you set baseUrl (or use gateway.bind=custom + gateway.customBindHost).
• Remote viewer misses are throttled to reduce token-guess abuse.
• PNG or PDF rendering requires a Chromium-compatible browser. Set browser.executablePath if auto-detection is not enough.
• If your delivery channel compresses images heavily (for example Telegram or WhatsApp), prefer fileFormat: "pdf" to preserve readability.
• N unmodified lines rows may not always include expand controls for patch input, because many patch hunks do not carry full expandable context data.
• Diff rendering is powered by Diffs.