diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
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--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,16 @@
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[project]
+name = "dpy_cache"
+version = "0.1.0"
+description = "Persist images/files to a Discord storage channel and get durable, re-resolvable CDN references — config-free, injectable, installable."
+requires-python = ">=3.10"
+dependencies = [
+    "discord.py>=2.0",
+    "aiohttp>=3.8",
+]
+
+[tool.hatch.build.targets.wheel]
+packages = ["src/dpy_cache"]
diff --git a/src/dpy_cache/__init__.py b/src/dpy_cache/__init__.py
new file mode 100644
index 0000000..ac390cc
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+++ b/src/dpy_cache/__init__.py
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+"""dpy_cache — persist images/files to discord and get durable, re-resolvable references
+
+see :mod:`dpy_cache.dpy_cache` for the full module docstring, api, and error contract
+"""
+from .dpy_cache import (
+    MAX_ATTACHMENTS_PER_MESSAGE,
+    CacheResult,
+    DPYCache,
+    DPYCacheError,
+    FileContent,
+    FileRef,
+)
+
+__version__ = "0.1.0"
+
+__all__ = [
+    "DPYCache",
+    "DPYCacheError",
+    "FileRef",
+    "CacheResult",
+    "FileContent",
+    "MAX_ATTACHMENTS_PER_MESSAGE",
+    "__version__",
+]
diff --git a/src/dpy_cache/dpy_cache.py b/src/dpy_cache/dpy_cache.py
new file mode 100644
index 0000000..b8009fe
--- /dev/null
+++ b/src/dpy_cache/dpy_cache.py
@@ -0,0 +1,264 @@
+"""persist images/files to discord by uploading to a storage channel, returning durable
+references (message jump url + per-file cdn urls keyed by original filename)
+
+mental model
+------------
+a discord attachment url is effectively permanent storage: upload a file to a channel once
+and the attachment lives on discord's cdn forever. this lib wraps "upload to a storage
+channel, hand me back the urls" so a bot can stash content and reference it later by its
+original filename.
+
+caveat that shapes the api: since late 2023 discord attachment cdn urls are SIGNED and the
+signature EXPIRES (~24h). the attachment itself is permanent; only the url's ``ex``/``is``/
+``hm`` params go stale, so a raw stored url 403s after expiry. this lib also returns a
+re-resolvable ``FileRef`` and a one-call :meth:`DPYCache.resolve` that re-fetches the
+message and hands back a freshly-signed url.
+
+usage (the headline is dead-simple single-file caching)::
+
+    cache = DPYCache(bot.get_channel(STORAGE_CHANNEL_ID))
+
+    url = (await cache.cache_one("img.png", image_bytes)).url    # raw bytes -> url
+    url = (await cache.cache_url("img.png", "https://...")).url  # remote url -> url
+
+several files at once (batches automatically over 10/message)::
+
+    result = await cache.cache({"avatar.png": avatar_bytes, "banner.png": "/tmp/banner.png"})
+    result.files["avatar.png"].url   # cdn url now
+    result.message_url               # jump link(s) to the stored message(s)
+
+    fresh = await cache.resolve(result.files["avatar.png"])  # later, if the url may be stale
+
+injection / config contract
+---------------------------
+inject the resolved discord channel object; the lib holds no client and reads no global
+config. it calls ``.send`` / ``.fetch_message`` on the channel directly, so any
+``discord.abc.Messageable`` that supports both (TextChannel, Thread) works. the bot must
+already have access to the channel; an inaccessible or bad channel raises discord's own
+error on first use.
+
+error contract (fail-loud)
+--------------------------
+nothing is swallowed. lib-specific invariants raise :class:`DPYCacheError` (attachment-count
+mismatch after a send, ``cache_url`` non-200, a ``lookup`` jump-url pointing at a different
+channel than the injected one). unnamed ``bytes`` in a list input raises ``ValueError``. raw
+discord errors (``Forbidden`` / ``HTTPException`` / ``NotFound``) propagate UNWRAPPED so
+callers can still branch on discord's types.
+"""
+from __future__ import annotations
+
+import io
+import logging
+import os
+from dataclasses import dataclass
+from typing import Union
+
+import aiohttp
+import discord
+
+log = logging.getLogger(__name__)
+
+MAX_ATTACHMENTS_PER_MESSAGE = 10
+
+FileContent = Union[bytes, str, "os.PathLike[str]", discord.File]
+
+
+class DPYCacheError(Exception):
+    """raised for dpy_cache's own invariants (count mismatch, remote fetch failure,
+    channel mismatch); raw discord errors propagate unwrapped instead"""
+
+
+@dataclass
+class FileRef:
+    """a durable reference to one cached attachment; ``url`` may expire (~24h), re-fetch a
+    fresh one via :meth:`DPYCache.resolve`"""
+
+    filename: str
+    url: str
+    message_id: int
+    channel_id: int
+    attachment_id: int
+
+
+@dataclass
+class CacheResult:
+    """result of a :meth:`DPYCache.cache` call; ``message_url`` is a single jump url for one
+    batch or a list of jump urls when the input spanned more than one message"""
+
+    message_url: Union[str, list[str]]
+    files: dict[str, FileRef]
+
+
+def _basename(path: "str | os.PathLike[str]") -> str:
+    """filename portion of a path-like, as the map key for list inputs"""
+    return os.path.basename(os.fspath(path))
+
+
+def _ref_from_attachment(name: str, attachment: discord.Attachment, message: discord.Message) -> FileRef:
+    """build a FileRef from a sent attachment and its message"""
+    return FileRef(
+        filename=name,
+        url=attachment.url,
+        message_id=message.id,
+        channel_id=message.channel.id,
+        attachment_id=attachment.id,
+    )
+
+
+class DPYCache:
+    """upload files to an injected storage channel and hand back durable references"""
+
+    def __init__(self, channel: discord.abc.Messageable) -> None:
+        """store the injected storage channel; caller resolves it, lib holds no client"""
+        self._channel = channel
+
+    async def cache(
+        self,
+        files: "dict[str, FileContent] | list[FileContent]",
+        *,
+        content: "str | None" = None,
+    ) -> CacheResult:
+        """upload files to the storage channel (batching over 10/message) and return refs
+        keyed by original filename; raises on unnamed bytes, count mismatch, or a discord
+        send error"""
+        items = self._normalize(files)
+        merged: dict[str, FileRef] = {}
+        jump_urls: list[str] = []
+
+        for start in range(0, len(items), MAX_ATTACHMENTS_PER_MESSAGE):
+            group = items[start:start + MAX_ATTACHMENTS_PER_MESSAGE]
+            discord_files = [self._to_file(name, source) for name, source in group]
+            try:
+                message = await self._channel.send(content=content, files=discord_files)
+            except (discord.Forbidden, discord.HTTPException):
+                log.error("dpy_cache: send of %d file(s) to the storage channel failed", len(group))
+                raise
+
+            attachments = list(message.attachments)
+            if len(attachments) != len(group):
+                sent_names = [name for name, _ in group]
+                got = len(attachments)
+                missing = sent_names[got:] if got < len(sent_names) else sent_names
+                raise DPYCacheError(
+                    f"discord returned {got} attachment(s) for {len(group)} sent file(s); "
+                    f"dropped: {', '.join(missing)}"
+                )
+
+            for (name, _), attachment in zip(group, attachments):
+                merged[name] = _ref_from_attachment(name, attachment, message)
+            jump_urls.append(message.jump_url)
+
+        message_url: "str | list[str]" = jump_urls[0] if len(jump_urls) == 1 else jump_urls
+        return CacheResult(message_url=message_url, files=merged)
+
+    async def cache_one(
+        self,
+        name: str,
+        data: FileContent,
+        *,
+        content: "str | None" = None,
+    ) -> FileRef:
+        """cache a single file, return its ref"""
+        result = await self.cache({name: data}, content=content)
+        return result.files[name]
+
+    async def cache_url(
+        self,
+        name: str,
+        url: str,
+        *,
+        content: "str | None" = None,
+    ) -> FileRef:
+        """fetch a remote url then cache its bytes as ``name``; raises DPYCacheError on
+        non-200"""
+        async with aiohttp.ClientSession() as session:
+            async with session.get(url) as response:
+                if response.status != 200:
+                    raise DPYCacheError(f"cache_url: GET {url} returned status {response.status}")
+                data = await response.read()
+        return await self.cache_one(name, data, content=content)
+
+    async def resolve(self, ref: FileRef) -> str:
+        """re-fetch the message and return a fresh (unexpired) cdn url for the attachment;
+        raises if the message or attachment is gone (never a stale url)
+
+        a gone MESSAGE propagates discord's own ``NotFound`` from ``fetch_message``; a gone
+        ATTACHMENT on a still-live message raises :class:`DPYCacheError` (the lib's own domain
+        fault) rather than a fabricated discord internal error"""
+        message = await self._channel.fetch_message(ref.message_id)
+        for attachment in message.attachments:
+            if attachment.id == ref.attachment_id:
+                return attachment.url
+        raise DPYCacheError(
+            f"attachment {ref.attachment_id} ({ref.filename}) no longer on message {ref.message_id}"
+        )
+
+    async def lookup(self, message: "str | int | discord.Message") -> dict[str, FileRef]:
+        """reverse lookup: a jump-url, message id, or Message -> {filename: FileRef}; raises
+        (NotFound) if the message is gone, never an empty map for a missing message"""
+        resolved = await self._resolve_message(message)
+        return {
+            attachment.filename: _ref_from_attachment(attachment.filename, attachment, resolved)
+            for attachment in resolved.attachments
+        }
+
+    def _normalize(self, files: "dict[str, FileContent] | list[FileContent]") -> "list[tuple[str, FileContent]]":
+        """normalize dict/list input to an ordered list of (name, source); raises ValueError
+        on unnamed bytes in a list"""
+        if isinstance(files, dict):
+            return list(files.items())
+
+        items: "list[tuple[str, FileContent]]" = []
+        for source in files:
+            if isinstance(source, discord.File):
+                items.append((source.filename, source))
+            elif isinstance(source, (str, os.PathLike)):
+                items.append((_basename(source), source))
+            elif isinstance(source, (bytes, bytearray)):
+                raise ValueError(
+                    "raw bytes in a list input have no filename; pass a dict {name: bytes} "
+                    "or a discord.File for named bytes"
+                )
+            else:
+                raise ValueError(f"unsupported file content type in list: {type(source).__name__}")
+        return items
+
+    def _to_file(self, name: str, source: FileContent) -> discord.File:
+        """build a fresh discord.File for ``source`` named ``name``; a fresh File is built
+        per send so the source survives multi-batch and retries"""
+        if isinstance(source, discord.File):
+            source.filename = name
+            return source
+        if isinstance(source, (bytes, bytearray)):
+            return discord.File(io.BytesIO(bytes(source)), filename=name)
+        if isinstance(source, (str, os.PathLike)):
+            return discord.File(source, filename=name)
+        raise ValueError(f"unsupported file content type: {type(source).__name__}")
+
+    async def _resolve_message(self, message: "str | int | discord.Message") -> discord.Message:
+        """turn a jump-url / id / Message into a fetched Message on the injected channel"""
+        if isinstance(message, discord.Message):
+            return message
+        if isinstance(message, int):
+            return await self._channel.fetch_message(message)
+        if isinstance(message, str):
+            channel_id, message_id = self._parse_jump_url(message)
+            if channel_id is not None and channel_id != self._channel.id:
+                raise DPYCacheError(
+                    f"lookup jump-url targets channel {channel_id} but the injected channel is "
+                    f"{self._channel.id}; this lib holds no client and can only fetch its own channel"
+                )
+            return await self._channel.fetch_message(message_id)
+        raise ValueError(f"unsupported lookup input type: {type(message).__name__}")
+
+    @staticmethod
+    def _parse_jump_url(url: str) -> "tuple[int | None, int]":
+        """parse (channel_id, message_id) out of a discord jump url; raises DPYCacheError on
+        a malformed url"""
+        parts = url.rstrip("/").split("/")
+        try:
+            message_id = int(parts[-1])
+            channel_id = int(parts[-2])
+        except (IndexError, ValueError):
+            raise DPYCacheError(f"lookup: not a valid discord jump url: {url}")
+        return channel_id, message_id