feat(hooks): add read-image-resizer hook

Intercepts Read tool output with image attachments and resizes to comply with Anthropic API limits (≤1568px long edge, ≤5MB). Only activates for Anthropic provider sessions and appends resize metadata (original/new resolution, token count) to tool output.

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

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

src/hooks/read-image-resizer/image-dimensions.test.ts

@@ -0,0 +1,108 @@
+/// <reference types="bun-types" />
+
+import { describe, expect, it } from "bun:test"
+
+import { parseImageDimensions } from "./image-dimensions"
+
+const PNG_1X1_DATA_URL =
+  "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg=="
+
+const GIF_1X1_DATA_URL =
+  "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"
+
+function createPngDataUrl(width: number, height: number): string {
+  const buf = Buffer.alloc(33)
+  buf.set([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a], 0)
+  buf.writeUInt32BE(13, 8)
+  buf.set([0x49, 0x48, 0x44, 0x52], 12)
+  buf.writeUInt32BE(width, 16)
+  buf.writeUInt32BE(height, 20)
+  return `data:image/png;base64,${buf.toString("base64")}`
+}
+
+function createGifDataUrl(width: number, height: number): string {
+  const buf = Buffer.alloc(10)
+  buf.set([0x47, 0x49, 0x46, 0x38, 0x39, 0x61], 0)
+  buf.writeUInt16LE(width, 6)
+  buf.writeUInt16LE(height, 8)
+  return `data:image/gif;base64,${buf.toString("base64")}`
+}
+
+describe("parseImageDimensions", () => {
+  it("parses PNG 1x1 dimensions", () => {
+    //#given
+    const dataUrl = PNG_1X1_DATA_URL
+
+    //#when
+    const result = parseImageDimensions(dataUrl, "image/png")
+
+    //#then
+    expect(result).toEqual({ width: 1, height: 1 })
+  })
+
+  it("parses PNG dimensions from IHDR", () => {
+    //#given
+    const dataUrl = createPngDataUrl(3000, 2000)
+
+    //#when
+    const result = parseImageDimensions(dataUrl, "image/png")
+
+    //#then
+    expect(result).toEqual({ width: 3000, height: 2000 })
+  })
+
+  it("parses GIF 1x1 dimensions", () => {
+    //#given
+    const dataUrl = GIF_1X1_DATA_URL
+
+    //#when
+    const result = parseImageDimensions(dataUrl, "image/gif")
+
+    //#then
+    expect(result).toEqual({ width: 1, height: 1 })
+  })
+
+  it("parses GIF dimensions from logical screen descriptor", () => {
+    //#given
+    const dataUrl = createGifDataUrl(320, 240)
+
+    //#when
+    const result = parseImageDimensions(dataUrl, "image/gif")
+
+    //#then
+    expect(result).toEqual({ width: 320, height: 240 })
+  })
+
+  it("returns null for empty input", () => {
+    //#given
+    const dataUrl = ""
+
+    //#when
+    const result = parseImageDimensions(dataUrl, "image/png")
+
+    //#then
+    expect(result).toBeNull()
+  })
+
+  it("returns null for too-short PNG buffer", () => {
+    //#given
+    const dataUrl = "data:image/png;base64,AAAA"
+
+    //#when
+    const result = parseImageDimensions(dataUrl, "image/png")
+
+    //#then
+    expect(result).toBeNull()
+  })
+
+  it("returns null for unsupported mime type", () => {
+    //#given
+    const dataUrl = PNG_1X1_DATA_URL
+
+    //#when
+    const result = parseImageDimensions(dataUrl, "image/heic")
+
+    //#then
+    expect(result).toBeNull()
+  })
+})