fix(opencode): add -- separator before prompt to prevent --file from consuming it

OpenCode CLI's --file flag is a yargs [array] type that greedily
consumes subsequent arguments as file paths. Without a -- separator,
the prompt text following --file was parsed as a filename, causing
"File not found" errors when images were attached.

Reported-by: community user via image analysis
Made-with: Cursor

agent/opencode/session.go

@@ -169,8 +169,9 @@ func (s *opencodeSession) buildRunArgs(prompt string, imagePaths []string, chatI
 		args = append(args, "--file", imagePath)
 	}
 
-	// Append prompt as positional arg.
-	args = append(args, prompt)
+	// Use "--" to separate flags from the positional prompt so that
+	// --file (yargs [array]) does not greedily consume the prompt text.
+	args = append(args, "--", prompt)
 	return args
 }
 

agent/opencode/session_test.go

@@ -112,7 +112,7 @@ func TestOpencodeSessionBuildRunArgsIncludesImagesAsFiles(t *testing.T) {
 		"--thinking",
 		"--file", "/tmp/a.png",
 		"--file", "/tmp/b.jpg",
-		"describe these images",
+		"--", "describe these images",
 	}
 	if !reflect.DeepEqual(got, want) {
 		t.Fatalf("args = %#v, want %#v", got, want)