feat(server): support image attachments in OpenCode agent prompts

Adds logic to process file parts and convert image attachments into data URLs for the OpenCode provider, replacing the previous behavior that stripped non-text parts.

packages/server/src/server/agent/providers/opencode-agent.test.ts

@@ -315,6 +315,23 @@ const hasOpenCode = isBinaryInstalled("opencode");
 });
 
 describe("OpenCode adapter context-window normalization", () => {
+  test("builds OpenCode file parts for image prompt blocks", () => {
+    expect(
+      __openCodeInternals.buildOpenCodePromptParts([
+        { type: "text", text: "Describe this image." },
+        { type: "image", mimeType: "image/png", data: "YWJjMTIz" },
+      ]),
+    ).toEqual([
+      { type: "text", text: "Describe this image." },
+      {
+        type: "file",
+        mime: "image/png",
+        filename: "attachment-1.png",
+        url: "data:image/png;base64,YWJjMTIz",
+      },
+    ]);
+  });
+
   test("preserves provider catalog context limit in model metadata", () => {
     const definition = __openCodeInternals.buildOpenCodeModelDefinition(
       { id: "openai", name: "OpenAI" },

packages/server/src/server/agent/providers/opencode-agent.ts

@@ -4,8 +4,10 @@ import {
   createOpencodeClient,
   type AssistantMessage as OpenCodeAssistantMessage,
   type Event as OpenCodeEvent,
+  type FilePartInput as OpenCodeFilePartInput,
   type OpencodeClient,
   type Part as OpenCodePart,
+  type TextPartInput as OpenCodeTextPartInput,
 } from "@opencode-ai/sdk/v2/client";
 import net from "node:net";
 import type { Logger } from "pino";
@@ -494,7 +496,66 @@ function hasNormalizedOpenCodeUsage(usage: AgentUsage): boolean {
   ].some((value) => typeof value === "number" && Number.isFinite(value));
 }
 
+function getOpenCodeAttachmentExtension(mimeType: string): string {
+  switch (mimeType) {
+    case "image/png":
+      return "png";
+    case "image/jpeg":
+      return "jpg";
+    case "image/webp":
+      return "webp";
+    case "image/gif":
+      return "gif";
+    case "image/svg+xml":
+      return "svg";
+    default:
+      return "bin";
+  }
+}
+
+function toOpenCodeDataUrl(mimeType: string, data: string): { mimeType: string; url: string } {
+  const match = data.match(/^data:([^;,]+);base64,(.+)$/);
+  if (match) {
+    return {
+      mimeType: match[1] ?? mimeType,
+      url: data,
+    };
+  }
+  return {
+    mimeType,
+    url: `data:${mimeType};base64,${data}`,
+  };
+}
+
+function buildOpenCodePromptParts(
+  prompt: AgentPromptInput,
+): Array<OpenCodeTextPartInput | OpenCodeFilePartInput> {
+  if (typeof prompt === "string") {
+    return [{ type: "text", text: prompt }];
+  }
+  let attachmentOrdinal = 0;
+  const output: Array<OpenCodeTextPartInput | OpenCodeFilePartInput> = [];
+  for (const part of prompt) {
+    if (part.type === "text") {
+      output.push({ type: "text", text: part.text });
+      continue;
+    }
+    attachmentOrdinal += 1;
+    const normalized = toOpenCodeDataUrl(part.mimeType, part.data);
+    output.push({
+      type: "file",
+      mime: normalized.mimeType,
+      filename: `attachment-${attachmentOrdinal}.${getOpenCodeAttachmentExtension(
+        normalized.mimeType,
+      )}`,
+      url: normalized.url,
+    });
+  }
+  return output;
+}
+
 export const __openCodeInternals = {
+  buildOpenCodePromptParts,
   buildOpenCodeModelContextWindowLookup,
   buildOpenCodeModelDefinition,
   buildOpenCodeModelLookupKey,
@@ -1436,7 +1497,7 @@ class OpenCodeAgentSession implements AgentSession {
     this.accumulatedUsage =
       contextWindowMaxTokens !== undefined ? { contextWindowMaxTokens } : {};
 
-    const parts = this.buildPromptParts(prompt);
+    const parts = buildOpenCodePromptParts(prompt);
     const model = this.parseModel(this.config.model);
     const thinkingOptionId = this.config.thinkingOptionId;
     const effectiveVariant = thinkingOptionId ?? undefined;
@@ -1862,15 +1923,6 @@ class OpenCodeAgentSession implements AgentSession {
     this.activeForegroundTurnId = null;
   }
 
-  private buildPromptParts(prompt: AgentPromptInput): Array<{ type: "text"; text: string }> {
-    if (typeof prompt === "string") {
-      return [{ type: "text", text: prompt }];
-    }
-    return prompt
-      .filter((p): p is { type: "text"; text: string } => p.type === "text")
-      .map((p) => ({ type: "text", text: p.text }));
-  }
-
   private parseSlashCommandInput(text: string): { commandName: string; args?: string } | null {
     const trimmed = text.trim();
     if (!trimmed.startsWith("/") || trimmed.length <= 1) {