fix(look-at): handle JSON parse errors from session.prompt gracefully (#1216)

When multimodal-looker agent returns empty/malformed response, the SDK
throws 'JSON Parse error: Unexpected EOF'. This commit adds try-catch
around session.prompt() to provide user-friendly error message with
troubleshooting guidance.

- Add error handling for JSON parse errors with detailed guidance
- Add error handling for generic prompt failures
- Add test cases for both error scenarios

src/tools/look-at/tools.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { normalizeArgs, validateArgs } from "./tools"
+import { normalizeArgs, validateArgs, createLookAt } from "./tools"
 
 describe("look-at tool", () => {
   describe("normalizeArgs", () => {
@@ -70,4 +70,80 @@ describe("look-at tool", () => {
       expect(error).toContain("file_path")
     })
   })
+
+  describe("createLookAt error handling", () => {
+    // #given session.prompt에서 JSON parse 에러 발생
+    // #when LookAt 도구 실행
+    // #then 사용자 친화적 에러 메시지 반환
+    test("handles JSON parse error from session.prompt gracefully", async () => {
+      const mockClient = {
+        session: {
+          get: async () => ({ data: { directory: "/project" } }),
+          create: async () => ({ data: { id: "ses_test_json_error" } }),
+          prompt: async () => {
+            throw new Error("JSON Parse error: Unexpected EOF")
+          },
+          messages: async () => ({ data: [] }),
+        },
+      }
+
+      const tool = createLookAt({
+        client: mockClient,
+        directory: "/project",
+      } as any)
+
+      const toolContext = {
+        sessionID: "parent-session",
+        messageID: "parent-message",
+        agent: "sisyphus",
+        abort: new AbortController().signal,
+      }
+
+      const result = await tool.execute(
+        { file_path: "/test/file.png", goal: "analyze image" },
+        toolContext
+      )
+
+      expect(result).toContain("Error: Failed to analyze file")
+      expect(result).toContain("malformed response")
+      expect(result).toContain("multimodal-looker")
+      expect(result).toContain("image/png")
+    })
+
+    // #given session.prompt에서 일반 에러 발생
+    // #when LookAt 도구 실행
+    // #then 원본 에러 메시지 포함한 에러 반환
+    test("handles generic prompt error gracefully", async () => {
+      const mockClient = {
+        session: {
+          get: async () => ({ data: { directory: "/project" } }),
+          create: async () => ({ data: { id: "ses_test_generic_error" } }),
+          prompt: async () => {
+            throw new Error("Network connection failed")
+          },
+          messages: async () => ({ data: [] }),
+        },
+      }
+
+      const tool = createLookAt({
+        client: mockClient,
+        directory: "/project",
+      } as any)
+
+      const toolContext = {
+        sessionID: "parent-session",
+        messageID: "parent-message",
+        agent: "sisyphus",
+        abort: new AbortController().signal,
+      }
+
+      const result = await tool.execute(
+        { file_path: "/test/file.pdf", goal: "extract text" },
+        toolContext
+      )
+
+      expect(result).toContain("Error: Failed to send prompt")
+      expect(result).toContain("Network connection failed")
+    })
+  })
 })

src/tools/look-at/tools.ts

@@ -131,6 +131,7 @@ Original error: ${createResult.error}`
       log(`[look_at] Created session: ${sessionID}`)
 
       log(`[look_at] Sending prompt with file passthrough to session ${sessionID}`)
+      try {
         await ctx.client.session.prompt({
           path: { id: sessionID },
           body: {
@@ -147,6 +148,32 @@ Original error: ${createResult.error}`
             ],
           },
         })
+      } catch (promptError) {
+        const errorMessage = promptError instanceof Error ? promptError.message : String(promptError)
+        log(`[look_at] Prompt error:`, promptError)
+
+        const isJsonParseError = errorMessage.includes("JSON") && (errorMessage.includes("EOF") || errorMessage.includes("parse"))
+        if (isJsonParseError) {
+          return `Error: Failed to analyze file - received malformed response from multimodal-looker agent.
+
+This typically occurs when:
+1. The multimodal-looker model is not available or not connected
+2. The model does not support this file type (${mimeType})
+3. The API returned an empty or truncated response
+
+File: ${args.file_path}
+MIME type: ${mimeType}
+
+Try:
+- Ensure a vision-capable model (e.g., gemini-3-flash, gpt-5.2) is available
+- Check provider connections in opencode settings
+- For text files like .md, .txt, use the Read tool instead
+
+Original error: ${errorMessage}`
+        }
+
+        return `Error: Failed to send prompt to multimodal-looker agent: ${errorMessage}`
+      }
 
       log(`[look_at] Prompt sent, fetching messages...`)