Q13: messages carry their attachments; agents read them by file_id

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main/services/agent-attachment-tools.ts

@@ -0,0 +1,54 @@
+import type { DatabaseSync } from "node:sqlite";
+import { readFileSync } from "node:fs";
+import { FILE_SCAN_STATE } from "../../shared/domain";
+import { requireString } from "./agent-tool-args";
+import type { AgentToolContext, AgentToolDeps } from "./agent-tools";
+import type { JsonRecord } from "./provider-http";
+import type { ToolDefinition } from "./provider-tool-turn";
+
+const ATTACHMENT_CHAR_LIMIT = 24_000;
+
+export const ATTACHMENT_TOOLS: ToolDefinition[] = [
+  {
+    name: "read_attachment",
+    description: "Read a file attached to a message or handed off to you, by the file_id shown next to the message.",
+    parameters: {
+      type: "object",
+      additionalProperties: false,
+      properties: { file_id: { type: "string" } },
+      required: ["file_id"],
+    },
+  },
+];
+
+/** " [attachments: a.md (file_id=…)]" for a message, or "". */
+export function attachmentNote(db: DatabaseSync, messageId: string): string {
+  const files = db.prepare(`
+    select f.id, f.name from chat_attachments ca join file_objects f on f.id = ca.file_id
+    where ca.message_id = ? order by f.name
+  `).all(messageId) as Array<{ id: string; name: string }>;
+  if (files.length === 0) return "";
+  return ` [attachments: ${files.map((file) => `${file.name} (file_id=${file.id})`).join(", ")}]`;
+}
+
+export function readAttachmentTool(deps: AgentToolDeps, ctx: AgentToolContext, args: JsonRecord): string {
+  const fileId = requireString(args.file_id, "file_id");
+  const file = deps.db.prepare("select name, storage_path, scan_state from file_objects where id = ? and org_id = ?")
+    .get(fileId, ctx.orgId) as { name: string; storage_path: string; scan_state: string } | undefined;
+  if (!file) throw new Error(`No file with file_id "${fileId}".`);
+  if (file.scan_state !== FILE_SCAN_STATE.APPROVED) throw new Error(`${file.name} was blocked by the file scan and cannot be read.`);
+  const bytes = readFileSync(file.storage_path);
+  const content = utf8Text(bytes);
+  if (content === null) return `${file.name} is a binary file (${bytes.length} bytes); it has no text to read.`;
+  if (content.length <= ATTACHMENT_CHAR_LIMIT) return content;
+  return `${content.slice(0, ATTACHMENT_CHAR_LIMIT)}\n\n[truncated: showing the first ${ATTACHMENT_CHAR_LIMIT} of ${content.length} characters]`;
+}
+
+function utf8Text(bytes: Buffer): string | null {
+  if (bytes.includes(0)) return null;
+  try {
+    return new TextDecoder("utf-8", { fatal: true }).decode(bytes);
+  } catch {
+    return null;
+  }
+}