diff --git a/adapters/common/attachment/__tests__/image-block-watcher.test.ts b/adapters/common/attachment/__tests__/image-block-watcher.test.ts
new file mode 100644
index 00000000..01d0775b
--- /dev/null
+++ b/adapters/common/attachment/__tests__/image-block-watcher.test.ts
@@ -0,0 +1,79 @@
+import { describe, it, expect } from 'bun:test'
+import { ImageBlockWatcher } from '../image-block-watcher.js'
+
+describe('ImageBlockWatcher', () => {
+  it('extracts a markdown image with http URL', () => {
+    const w = new ImageBlockWatcher()
+    const out = w.feed('Here is ![alt](https://example.com/foo.png) an image.')
+    expect(out.length).toBe(1)
+    const source = out[0]!.source
+    expect(source.kind).toBe('url')
+    if (source.kind === 'url') {
+      expect(source.url).toBe('https://example.com/foo.png')
+    }
+    expect(out[0]!.alt).toBe('alt')
+  })
+
+  it('extracts a markdown image with absolute local path', () => {
+    const w = new ImageBlockWatcher()
+    const out = w.feed('![cat](/tmp/cat.jpg)')
+    expect(out.length).toBe(1)
+    const source = out[0]!.source
+    expect(source.kind).toBe('path')
+    if (source.kind === 'path') {
+      expect(source.path).toBe('/tmp/cat.jpg')
+    }
+  })
+
+  it('extracts a markdown image with file:// URL as path', () => {
+    const w = new ImageBlockWatcher()
+    const out = w.feed('![x](file:///var/img/x.png)')
+    const source = out[0]!.source
+    expect(source.kind).toBe('path')
+    if (source.kind === 'path') expect(source.path).toBe('/var/img/x.png')
+  })
+
+  it('extracts a data URI as base64', () => {
+    const w = new ImageBlockWatcher()
+    const out = w.feed('![inline](data:image/png;base64,AAAA)')
+    const source = out[0]!.source
+    expect(source.kind).toBe('base64')
+    if (source.kind === 'base64') {
+      expect(source.mime).toBe('image/png')
+      expect(source.data).toBe('AAAA')
+    }
+  })
+
+  it('deduplicates the same image across multiple feeds', () => {
+    const w = new ImageBlockWatcher()
+    const a = w.feed('![](https://x/y.png)')
+    const b = w.feed(' repeated ![](https://x/y.png) again')
+    expect(a.length).toBe(1)
+    expect(b.length).toBe(0)
+  })
+
+  it('handles images split across feed boundaries', () => {
+    const w = new ImageBlockWatcher()
+    const a = w.feed('a ![al')
+    const b = w.feed('t](/tmp/x.png) b')
+    expect(a.length).toBe(0)
+    expect(b.length).toBe(1)
+    const source = b[0]!.source
+    expect(source.kind).toBe('path')
+    if (source.kind === 'path') expect(source.path).toBe('/tmp/x.png')
+  })
+
+  it('skips non-image markdown links', () => {
+    const w = new ImageBlockWatcher()
+    const out = w.feed('See [docs](https://example.com).')
+    expect(out.length).toBe(0)
+  })
+
+  it('drain() returns all accumulated uploads', () => {
+    const w = new ImageBlockWatcher()
+    w.feed('![a](/tmp/a.png)')
+    w.feed(' and ![b](/tmp/b.png)')
+    const all = w.drain()
+    expect(all.length).toBe(2)
+  })
+})
diff --git a/adapters/common/attachment/image-block-watcher.ts b/adapters/common/attachment/image-block-watcher.ts
new file mode 100644
index 00000000..cce5c826
--- /dev/null
+++ b/adapters/common/attachment/image-block-watcher.ts
@@ -0,0 +1,94 @@
+/**
+ * Pure, stateful extractor that watches a stream of assistant text for
+ * markdown image references (`![alt](source)`) and emits PendingUpload
+ * records. Used by IM adapters to know which images to upload to IM.
+ *
+ * - Buffers input so an image marker split across multiple feed() calls
+ *   still gets detected.
+ * - Dedups by fingerprint of the source so the same image is only emitted
+ *   once per watcher lifetime.
+ */
+
+import type { PendingUpload } from './attachment-types.js'
+
+// Matches a complete markdown image: ![alt](target)
+// `alt` may be empty; `target` stops at the first closing paren.
+const IMAGE_RE = /!\[([^\]]*)\]\(([^)\s]+)\)/g
+
+function fingerprint(raw: string): string {
+  let h = 5381
+  for (let i = 0; i < raw.length; i++) {
+    h = ((h << 5) + h) ^ raw.charCodeAt(i)
+  }
+  return (h >>> 0).toString(16)
+}
+
+function classify(target: string): PendingUpload['source'] | null {
+  if (target.startsWith('data:')) {
+    const m = /^data:([^;,]+);base64,(.+)$/.exec(target)
+    if (!m) return null
+    return { kind: 'base64', mime: m[1]!, data: m[2]! }
+  }
+  if (target.startsWith('file://')) {
+    return { kind: 'path', path: target.slice('file://'.length) }
+  }
+  if (target.startsWith('http://') || target.startsWith('https://')) {
+    return { kind: 'url', url: target }
+  }
+  if (target.startsWith('/')) {
+    return { kind: 'path', path: target }
+  }
+  return null // relative paths — skip, we can't resolve them safely
+}
+
+export class ImageBlockWatcher {
+  private buffer = ''
+  private seen = new Set<string>()
+  private accumulated: PendingUpload[] = []
+
+  /** Feed a new chunk of streaming text; returns any NEW PendingUploads. */
+  feed(chunk: string): PendingUpload[] {
+    this.buffer += chunk
+    const out: PendingUpload[] = []
+
+    IMAGE_RE.lastIndex = 0
+    let lastConsumedEnd = 0
+    let m: RegExpExecArray | null
+    while ((m = IMAGE_RE.exec(this.buffer)) !== null) {
+      const [, alt, target] = m
+      const source = classify(target!)
+      if (source) {
+        const id = fingerprint(`${source.kind}:${target}`)
+        if (!this.seen.has(id)) {
+          this.seen.add(id)
+          const pending: PendingUpload = { id, source, alt: alt || undefined }
+          out.push(pending)
+          this.accumulated.push(pending)
+        }
+      }
+      lastConsumedEnd = m.index + m[0].length
+    }
+
+    // Preserve tail that might contain a partially-received marker.
+    if (lastConsumedEnd > 0) {
+      this.buffer = this.buffer.slice(lastConsumedEnd)
+    }
+    if (this.buffer.length > 4096) {
+      this.buffer = this.buffer.slice(-2048)
+    }
+
+    return out
+  }
+
+  /** Return everything seen so far (for end-of-stream reconciliation). */
+  drain(): PendingUpload[] {
+    return [...this.accumulated]
+  }
+
+  /** Reset watcher state (use at /clear or new session). */
+  reset(): void {
+    this.buffer = ''
+    this.seen.clear()
+    this.accumulated = []
+  }
+}