fix(apiproxy): cancel attachment reads during export

Response-consumer cancellation already stopped lineage reads, persistence reads, and ZIP production, but the final attachment phase called readImage without the producer signal. A slow or stalled attachment backend could therefore keep working after the browser abandoned the download and prevent the producer from settling.\n\nExtend the attachment read seam with optional cancellation, forward it through the local backend into Node's filesystem read, and preserve the abort reason rather than wrapping it as a storage failure. The exporter now passes its combined request/consumer signal to every attachment read.\n\nCover both ownership boundaries: the local-store test proves filesystem forwarding and cancellation identity, while the assembled export test cancels a reader during a pending attachment provider call. Regenerate the Cordis API catalog and paired documentation so implementers can rely on the new contract.

packages/attachment/attachment-local/tests/store.spec.ts

@@ -9,12 +9,23 @@ import sharp from 'sharp'
 import type { ImageAttachmentLimits } from '@deepseek-ai/dsh-attachment'
 import { readImageFile, saveImageFile } from '../src/store.ts'
 
-const fsControl = vi.hoisted(() => ({ syncedDirectories: [] as string[] }))
+const fsControl = vi.hoisted(() => ({
+  readSignals: [] as AbortSignal[],
+  syncedDirectories: [] as string[],
+}))
 
 vi.mock('node:fs/promises', async (importOriginal) => {
   const actual = await importOriginal<typeof import('node:fs/promises')>()
   return {
     ...actual,
+    readFile(...args: Parameters<typeof actual.readFile>): ReturnType<typeof actual.readFile> {
+      const options = args[1]
+      if (typeof options === 'object' && options !== null) {
+        const signal = (options as { signal?: AbortSignal }).signal
+        if (signal !== undefined) fsControl.readSignals.push(signal)
+      }
+      return actual.readFile(...args)
+    },
     async open(...args: Parameters<typeof actual.open>): ReturnType<typeof actual.open> {
       if (args[1] === constants.O_RDONLY) fsControl.syncedDirectories.push(String(args[0]))
       return actual.open(...args)
@@ -130,6 +141,20 @@ describe('local attachment store', () => {
     await expect(readImageFile(storageRoot, ref)).resolves.toEqual({ ref, data: PNG })
   })
 
+  it('forwards read cancellation to the filesystem and preserves its reason', async () => {
+    const storageRoot = await root()
+    const ref = await saveImageFile(storageRoot, { data: PNG, mediaType: 'image/png' }, LIMITS)
+    const controller = new AbortController()
+    fsControl.readSignals.length = 0
+
+    await expect(readImageFile(storageRoot, ref, controller.signal)).resolves.toEqual({ ref, data: PNG })
+    expect(fsControl.readSignals).toEqual([controller.signal])
+
+    const cancellation = new Error('attachment read cancelled')
+    controller.abort(cancellation)
+    await expect(readImageFile(storageRoot, ref, controller.signal)).rejects.toBe(cancellation)
+  })
+
   it('rejects malformed bytes, mismatched declarations, byte limits, and decoded-pixel limits', async () => {
     const storageRoot = await root()
     await expect(saveImageFile(storageRoot, {