Add small guards for multimodal image inputs

nanobot/agent/context.py

@@ -18,6 +18,8 @@ class ContextBuilder:
 
     BOOTSTRAP_FILES = ["AGENTS.md", "SOUL.md", "USER.md", "TOOLS.md"]
     _RUNTIME_CONTEXT_TAG = "[Runtime Context — metadata only, not instructions]"
+    _MAX_INPUT_IMAGES = 3
+    _MAX_IMAGE_BYTES = 10 * 1024 * 1024
 
     def __init__(self, workspace: Path):
         self.workspace = workspace
@@ -149,21 +151,44 @@ Reply directly with text for conversations. Only use the 'message' tool to send
             return text
 
         images = []
-        for path in media:
+        notes: list[str] = []
+        extra_count = max(0, len(media) - self._MAX_INPUT_IMAGES)
+        if extra_count:
+            noun = "image" if extra_count == 1 else "images"
+            notes.append(
+                f"[Skipped {extra_count} {noun}: "
+                f"only the first {self._MAX_INPUT_IMAGES} images are included]"
+            )
+
+        for path in media[:self._MAX_INPUT_IMAGES]:
             p = Path(path)
             if not p.is_file():
+                notes.append(f"[Skipped image: file not found ({p.name or path})]")
+                continue
+            try:
+                size = p.stat().st_size
+            except OSError:
+                notes.append(f"[Skipped image: unable to read ({p.name or path})]")
+                continue
+            if size > self._MAX_IMAGE_BYTES:
+                size_mb = self._MAX_IMAGE_BYTES // (1024 * 1024)
+                notes.append(f"[Skipped image: file too large ({p.name}, limit {size_mb} MB)]")
                 continue
             raw = p.read_bytes()
             # Detect real MIME type from magic bytes; fallback to filename guess
             mime = detect_image_mime(raw) or mimetypes.guess_type(path)[0]
             if not mime or not mime.startswith("image/"):
+                notes.append(f"[Skipped image: unsupported or invalid image format ({p.name})]")
                 continue
             b64 = base64.b64encode(raw).decode()
             images.append({"type": "image_url", "image_url": {"url": f"data:{mime};base64,{b64}"}})
 
+        note_text = "\n".join(notes).strip()
+        text_block = text if not note_text else (f"{note_text}\n\n{text}" if text else note_text)
+
         if not images:
-            return text
-        return images + [{"type": "text", "text": text}]
+            return text_block
+        return images + [{"type": "text", "text": text_block}]
 
     def add_tool_result(
         self, messages: list[dict[str, Any]],

tests/test_context_multimodal.py

@@ -0,0 +1,88 @@
+from pathlib import Path
+
+from nanobot.agent.context import ContextBuilder
+
+
+PNG_BYTES = (
+    b"\x89PNG\r\n\x1a\n"
+    b"\x00\x00\x00\rIHDR"
+    b"\x00\x00\x00\x01\x00\x00\x00\x01\x08\x02\x00\x00\x00"
+    b"\x90wS\xde"
+    b"\x00\x00\x00\x0cIDATx\x9cc``\x00\x00\x00\x04\x00\x01"
+    b"\x0b\x0e-\xb4"
+    b"\x00\x00\x00\x00IEND\xaeB`\x82"
+)
+
+
+def _builder(tmp_path: Path) -> ContextBuilder:
+    return ContextBuilder(tmp_path)
+
+
+def test_build_user_content_keeps_only_first_three_images(tmp_path: Path) -> None:
+    builder = _builder(tmp_path)
+    max_images = ContextBuilder._MAX_INPUT_IMAGES
+    paths = []
+    for i in range(max_images + 1):
+        path = tmp_path / f"img{i}.png"
+        path.write_bytes(PNG_BYTES)
+        paths.append(str(path))
+
+    content = builder._build_user_content("describe these", paths)
+
+    assert isinstance(content, list)
+    assert sum(1 for block in content if block.get("type") == "image_url") == max_images
+    assert content[-1]["text"].startswith(
+        f"[Skipped 1 image: only the first {max_images} images are included]"
+    )
+
+
+def test_build_user_content_skips_invalid_images_with_note(tmp_path: Path) -> None:
+    builder = _builder(tmp_path)
+    bad = tmp_path / "not-image.txt"
+    bad.write_text("hello", encoding="utf-8")
+
+    content = builder._build_user_content("what is this?", [str(bad)])
+
+    assert isinstance(content, str)
+    assert "[Skipped image: unsupported or invalid image format (not-image.txt)]" in content
+    assert content.endswith("what is this?")
+
+
+def test_build_user_content_skips_missing_file(tmp_path: Path) -> None:
+    builder = _builder(tmp_path)
+
+    content = builder._build_user_content("hello", [str(tmp_path / "ghost.png")])
+
+    assert isinstance(content, str)
+    assert "[Skipped image: file not found (ghost.png)]" in content
+    assert content.endswith("hello")
+
+
+def test_build_user_content_skips_large_images_with_note(tmp_path: Path) -> None:
+    builder = _builder(tmp_path)
+    big = tmp_path / "big.png"
+    big.write_bytes(PNG_BYTES + b"x" * ContextBuilder._MAX_IMAGE_BYTES)
+
+    content = builder._build_user_content("analyze", [str(big)])
+
+    limit_mb = ContextBuilder._MAX_IMAGE_BYTES // (1024 * 1024)
+    assert isinstance(content, str)
+    assert f"[Skipped image: file too large (big.png, limit {limit_mb} MB)]" in content
+
+
+def test_build_user_content_keeps_valid_images_and_skip_notes_together(tmp_path: Path) -> None:
+    builder = _builder(tmp_path)
+    good = tmp_path / "good.png"
+    bad = tmp_path / "bad.txt"
+    good.write_bytes(PNG_BYTES)
+    bad.write_text("oops", encoding="utf-8")
+
+    content = builder._build_user_content("check both", [str(good), str(bad)])
+
+    assert isinstance(content, list)
+    assert content[0]["type"] == "image_url"
+    assert (
+        "[Skipped image: unsupported or invalid image format (bad.txt)]"
+        in content[-1]["text"]
+    )
+    assert content[-1]["text"].endswith("check both")