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/hook.ts

@@ -0,0 +1,197 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import type { ImageAttachment, ImageDimensions } from "./types"
+import { parseImageDimensions } from "./image-dimensions"
+import { calculateTargetDimensions, resizeImage } from "./image-resizer"
+import { log } from "../../shared"
+import { getSessionModel } from "../../shared/session-model-state"
+const SUPPORTED_IMAGE_MIMES = new Set(["image/png", "image/jpeg", "image/gif", "image/webp"])
+const TOKEN_DIVISOR = 750
+interface ResizeEntry {
+  filename: string
+  originalDims: ImageDimensions | null
+  resizedDims: ImageDimensions | null
+  status: "resized" | "within-limits" | "resize-skipped" | "unknown-dims"
+}
+function isReadTool(toolName: string): boolean {
+  return toolName.toLowerCase() === "read"
+}
+function asRecord(value: unknown): Record<string, unknown> | null {
+  if (!value || typeof value !== "object" || Array.isArray(value)) {
+    return null
+  }
+  return value as Record<string, unknown>
+}
+function isImageAttachmentRecord(
+  value: Record<string, unknown>,
+): value is Record<string, unknown> & ImageAttachment {
+  const filename = value.filename
+  return (
+    typeof value.mime === "string" &&
+    typeof value.url === "string" &&
+    (typeof filename === "undefined" || typeof filename === "string")
+  )
+}
+function extractImageAttachments(output: Record<string, unknown>): ImageAttachment[] {
+  const attachmentsValue = output.attachments
+  if (!Array.isArray(attachmentsValue)) {
+    return []
+  }
+  const attachments: ImageAttachment[] = []
+  for (const attachmentValue of attachmentsValue) {
+    const attachmentRecord = asRecord(attachmentValue)
+    if (!attachmentRecord) {
+      continue
+    }
+
+    const mime = attachmentRecord.mime
+    const url = attachmentRecord.url
+    if (typeof mime !== "string" || typeof url !== "string") {
+      continue
+    }
+
+    const normalizedMime = mime.toLowerCase()
+    if (!SUPPORTED_IMAGE_MIMES.has(normalizedMime)) {
+      continue
+    }
+
+    attachmentRecord.mime = normalizedMime
+    attachmentRecord.url = url
+    if (isImageAttachmentRecord(attachmentRecord)) {
+      attachments.push(attachmentRecord)
+    }
+  }
+
+  return attachments
+}
+function calculateTokens(width: number, height: number): number {
+  return Math.ceil((width * height) / TOKEN_DIVISOR)
+}
+function formatResizeAppendix(entries: ResizeEntry[]): string {
+  const header = entries.some((entry) => entry.status === "resized") ? "[Image Resize Info]" : "[Image Info]"
+  const lines = [`\n\n${header}`]
+
+  for (const entry of entries) {
+    if (entry.status === "unknown-dims" || !entry.originalDims) {
+      lines.push(`- ${entry.filename}: dimensions could not be parsed`)
+      continue
+    }
+
+    const original = entry.originalDims
+    const originalText = `${original.width}x${original.height}`
+    const originalTokens = calculateTokens(original.width, original.height)
+
+    if (entry.status === "within-limits") {
+      lines.push(`- ${entry.filename}: ${originalText} (within limits, tokens: ${originalTokens})`)
+      continue
+    }
+
+    if (entry.status === "resize-skipped") {
+      lines.push(`- ${entry.filename}: ${originalText} (resize skipped, tokens: ${originalTokens})`)
+      continue
+    }
+
+    if (!entry.resizedDims) {
+      lines.push(`- ${entry.filename}: ${originalText} (resize skipped, tokens: ${originalTokens})`)
+      continue
+    }
+
+    const resized = entry.resizedDims
+    const resizedText = `${resized.width}x${resized.height}`
+    const resizedTokens = calculateTokens(resized.width, resized.height)
+    lines.push(
+      `- ${entry.filename}: ${originalText} -> ${resizedText} (resized, tokens: ${originalTokens} -> ${resizedTokens})`,
+    )
+  }
+
+  return lines.join("\n")
+}
+function resolveFilename(attachment: ImageAttachment, index: number): string {
+  if (attachment.filename && attachment.filename.trim().length > 0) {
+    return attachment.filename
+  }
+
+  return `image-${index + 1}`
+}
+export function createReadImageResizerHook(_ctx: PluginInput) {
+  return {
+    "tool.execute.after": async (
+      input: { tool: string; sessionID: string; callID: string },
+      output: { title: string; output: string; metadata: unknown },
+    ) => {
+      if (!isReadTool(input.tool)) {
+        return
+      }
+
+      const sessionModel = getSessionModel(input.sessionID)
+      if (sessionModel?.providerID !== "anthropic") {
+        return
+      }
+
+      if (typeof output.output !== "string") {
+        return
+      }
+
+      const outputRecord = output as Record<string, unknown>
+      const attachments = extractImageAttachments(outputRecord)
+      if (attachments.length === 0) {
+        return
+      }
+
+      const entries: ResizeEntry[] = []
+      for (const [index, attachment] of attachments.entries()) {
+        const filename = resolveFilename(attachment, index)
+
+        try {
+          const originalDims = parseImageDimensions(attachment.url, attachment.mime)
+          if (!originalDims) {
+            entries.push({ filename, originalDims: null, resizedDims: null, status: "unknown-dims" })
+            continue
+          }
+
+          const targetDims = calculateTargetDimensions(originalDims.width, originalDims.height)
+          if (!targetDims) {
+            entries.push({
+              filename,
+              originalDims,
+              resizedDims: null,
+              status: "within-limits",
+            })
+            continue
+          }
+
+          const resizedResult = await resizeImage(attachment.url, attachment.mime, targetDims)
+          if (!resizedResult) {
+            entries.push({
+              filename,
+              originalDims,
+              resizedDims: null,
+              status: "resize-skipped",
+            })
+            continue
+          }
+
+          attachment.url = resizedResult.resizedDataUrl
+
+          entries.push({
+            filename,
+            originalDims: resizedResult.original,
+            resizedDims: resizedResult.resized,
+            status: "resized",
+          })
+        } catch (error) {
+          log("[read-image-resizer] attachment processing failed", {
+            error: error instanceof Error ? error.message : String(error),
+            filename,
+          })
+          entries.push({ filename, originalDims: null, resizedDims: null, status: "unknown-dims" })
+        }
+      }
+
+      if (entries.length === 0) {
+        return
+      }
+
+      output.output += formatResizeAppendix(entries)
+    },
+  }
+}