feat(mcp): add resource read tools (#33483)

packages/opencode/src/session/prompt.ts

@@ -66,6 +66,14 @@ globalThis.AI_SDK_LOG_WARNINGS = false
 
 const decodeMessageInfo = Schema.decodeUnknownExit(SessionV1.Info)
 const decodeMessagePart = Schema.decodeUnknownExit(SessionV1.Part)
+const MAX_MCP_RESOURCE_BLOB_BYTES = 10 * 1024 * 1024
+const SUPPORTED_MCP_RESOURCE_ATTACHMENT_MIMES = new Set([
+  "application/pdf",
+  "image/gif",
+  "image/jpeg",
+  "image/png",
+  "image/webp",
+])
 
 const STRUCTURED_OUTPUT_DESCRIPTION = `Use this tool to return your final response in the requested structured format.
 
@@ -77,6 +85,18 @@ IMPORTANT:
 
 const STRUCTURED_OUTPUT_SYSTEM_PROMPT = `IMPORTANT: The user has requested structured output. You MUST use the StructuredOutput tool to provide your final response. Do NOT respond with plain text - you MUST call the StructuredOutput tool with your answer formatted according to the schema.`
 
+function mcpResourceBase64Size(value: string) {
+  const trimmed = value.replace(/\s/g, "")
+  const padding = trimmed.endsWith("==") ? 2 : trimmed.endsWith("=") ? 1 : 0
+  return Math.max(0, Math.floor((trimmed.length * 3) / 4) - padding)
+}
+
+function formatMcpResourceBytes(value: number) {
+  if (value < 1024) return `${value} B`
+  if (value < 1024 * 1024) return `${Math.ceil(value / 1024)} KB`
+  return `${Math.ceil(value / (1024 * 1024))} MB`
+}
+
 function isOrphanedInterruptedTool(part: SessionV1.ToolPart) {
   // cleanup() marks abandoned tool_use blocks this way after retries/aborts.
   // They are not pending work and must not trigger an assistant-prefill request.
@@ -731,7 +751,8 @@ export const layer = Layer.effect(
               if (!content) throw new Error(`Resource not found: ${clientName}/${uri}`)
               const items = Array.isArray(content.contents) ? content.contents : [content.contents]
               for (const c of items) {
-                if ("text" in c && c.text) {
+                if (!c || typeof c !== "object") continue
+                if ("text" in c && typeof c.text === "string" && c.text) {
                   pieces.push({
                     messageID: info.id,
                     sessionID: input.sessionID,
@@ -739,18 +760,47 @@ export const layer = Layer.effect(
                     synthetic: true,
                     text: c.text,
                   })
-                } else if ("blob" in c && c.blob) {
-                  const mime = "mimeType" in c ? c.mimeType : part.mime
+                } else if ("blob" in c && typeof c.blob === "string" && c.blob) {
+                  const mime = "mimeType" in c && typeof c.mimeType === "string" ? c.mimeType : part.mime
+                  const filename = "uri" in c && typeof c.uri === "string" ? c.uri : part.filename
+                  const size = mcpResourceBase64Size(c.blob)
+                  if (!SUPPORTED_MCP_RESOURCE_ATTACHMENT_MIMES.has(mime)) {
+                    pieces.push({
+                      messageID: info.id,
+                      sessionID: input.sessionID,
+                      type: "text",
+                      synthetic: true,
+                      text: `[Binary MCP resource omitted: ${filename ?? uri} (${mime}, ${formatMcpResourceBytes(size)}) is not a supported attachment type]`,
+                    })
+                    continue
+                  }
+                  if (size > MAX_MCP_RESOURCE_BLOB_BYTES) {
+                    pieces.push({
+                      messageID: info.id,
+                      sessionID: input.sessionID,
+                      type: "text",
+                      synthetic: true,
+                      text: `[Binary MCP resource omitted: ${filename ?? uri} (${mime}, ${formatMcpResourceBytes(size)}) exceeds ${formatMcpResourceBytes(MAX_MCP_RESOURCE_BLOB_BYTES)}]`,
+                    })
+                    continue
+                  }
                   pieces.push({
                     messageID: info.id,
                     sessionID: input.sessionID,
                     type: "text",
                     synthetic: true,
-                    text: `[Binary content: ${mime}]`,
+                    text: `[Binary MCP resource attached: ${filename ?? uri} (${mime})]`,
+                  })
+                  pieces.push({
+                    messageID: info.id,
+                    sessionID: input.sessionID,
+                    type: "file",
+                    mime,
+                    filename,
+                    url: `data:${mime};base64,${c.blob}`,
                   })
                 }
               }
-              pieces.push({ ...part, messageID: info.id, sessionID: input.sessionID })
             } else {
               const error = Cause.squash(exit.cause)
               yield* Effect.logError("failed to read MCP resource", { error, clientName, uri })