fix(bridle): tell the model a binary attachment exists (CLEAN-57)

api/src/slices/bridle/domain/attachment.service.spec.ts

@@ -237,8 +237,11 @@ describe('BridleAttachmentService — text extraction', () => {
 
     expect(out.attachments[0].kind).toBe(BridleAttachmentKinds.Binary);
     expect(out.attachments[0].readableByAgent).toBe(false);
-    expect(out.text).toBe('read this');
-    expect(out.text).not.toContain('Attached file');
+    // Downgraded to binary: the model gets the unreadable-file notice, and
+    // none of the undecodable bytes reach the prompt as mojibake.
+    expect(out.text).toContain('read this');
+    expect(out.text).toContain('not readable');
+    expect(out.text).not.toContain('�');
   });
 
   it('downgrades a text-typed file containing NUL bytes', async () => {
@@ -253,7 +256,9 @@ describe('BridleAttachmentService — text extraction', () => {
     const out = await service.expand(AGENT, 'read this', ['t1']);
 
     expect(out.attachments[0].kind).toBe(BridleAttachmentKinds.Binary);
-    expect(out.text).toBe('read this');
+    expect(out.text).toContain('read this');
+    expect(out.text).toContain('not readable');
+    expect(out.text).not.toContain('ab');
   });
 
   it('preserves non-ASCII text intact', async () => {
@@ -302,7 +307,7 @@ describe('BridleAttachmentService — expansion to parts', () => {
     expect(out.text).toBe('what is this?');
   });
 
-  it('turns a binary into a file part and inlines nothing', async () => {
+  it('turns a binary into a file part and inlines an unreadable-file notice', async () => {
     const { service, gw } = makeService();
     gw.seed('b1', {
       name: 'report.pdf',
@@ -318,7 +323,28 @@ describe('BridleAttachmentService — expansion to parts', () => {
       name: 'report.pdf',
       mimeType: 'application/pdf',
     });
-    expect(out.text).toBe('read it');
+    // The runtime drops file parts before the model call, so without this
+    // notice the model would never learn the file exists at all.
+    expect(out.text).toContain('read it');
+    expect(out.text).toContain('report.pdf');
+    expect(out.text).toContain('not readable');
+    // Never the contents — only the reference.
+    expect(out.text).not.toContain('%PDF-1.7');
+  });
+
+  it('gives an attachment-only binary message a visible text body', async () => {
+    const { service, gw } = makeService();
+    gw.seed('b1', {
+      name: 'haha.xlsx',
+      mimeType:
+        'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+      size: 2,
+      body: Buffer.from('PK'),
+    });
+
+    const out = await service.expand(AGENT, '', ['b1']);
+
+    expect(out.text).toContain('haha.xlsx');
   });
 
   it('emits a file part AND inlined text for a text attachment', async () => {

api/src/slices/bridle/domain/attachment.service.ts

@@ -150,6 +150,12 @@ export class BridleAttachmentService {
         });
         if (kind === BridleAttachmentKinds.Text) {
           textBlocks.push(this.inlineTextBlock(stored));
+        } else {
+          // The runtime drops file parts before the model call, so without
+          // this line the model never learns the file exists — it would deny
+          // seeing an attachment the person is looking right at. The notice
+          // names the file and its limits; the contents stay unread.
+          textBlocks.push(BridleAttachmentService.binaryNoticeBlock(stored));
         }
       }
 
@@ -210,6 +216,20 @@ export class BridleAttachmentService {
     return `[Attached file: ${stored.name}]\n${fence}\n${body}${notice}\n${fence}`;
   }
 
+  /**
+   * What the model is told about a binary attachment: name, type, size —
+   * and that the contents are out of reach, so it answers honestly instead
+   * of denying the file exists.
+   */
+  static binaryNoticeBlock(stored: IBridleStoredAttachment): string {
+    return (
+      `[Attached file: ${stored.name} ` +
+      `(${stored.mimeType}, ${stored.size.toLocaleString('en-US')} bytes). ` +
+      `Its contents are not readable in this chat — it is delivered as a ` +
+      `named reference only.]`
+    );
+  }
+
   /** Path of the authenticated download route — never an S3 URL. */
   static urlFor(agentId: string, attachmentId: string): string {
     return `/api/agent/${encodeURIComponent(agentId)}/attachment/${attachmentId}`;