diff --git a/workspace/inbox.py b/workspace/inbox.py
index 94417243..6c7ea895 100644
--- a/workspace/inbox.py
+++ b/workspace/inbox.py
@@ -432,7 +432,17 @@ def _is_self_notify_row(row: dict[str, Any]) -> bool:
 
 
 def message_from_activity(row: dict[str, Any]) -> InboxMessage:
-    """Convert one /activity row into an InboxMessage."""
+    """Convert one /activity row into an InboxMessage.
+
+    Mutates ``row['request_body']`` in-place to swap any
+    ``platform-pending:`` URIs to the locally-staged ``workspace:`` URIs
+    (see ``inbox_uploads.rewrite_request_body``) — by the time the
+    upstream chat message arrives via this path, the upload-receive row
+    that staged the bytes has already populated the URI cache (lower
+    activity_logs.id, processed earlier in the same poll batch). A
+    cache miss leaves the URI untouched; the agent surfaces an
+    unresolvable URI rather than the inbox silently dropping the part.
+    """
     request_body = row.get("request_body")
     if isinstance(request_body, str):
         # The Go handler returns request_body as json.RawMessage; httpx
@@ -443,6 +453,14 @@ def message_from_activity(row: dict[str, Any]) -> InboxMessage:
         except (TypeError, ValueError):
             request_body = None
 
+    # Rewrite platform-pending: URIs → workspace: URIs in-place. Imported
+    # at call time to keep the import graph clean for the in-container
+    # path that doesn't use this module (also avoids a circular: the
+    # uploads module is small enough that re-importing per call is
+    # cheap, and the Python import cache makes it free after the first).
+    from inbox_uploads import rewrite_request_body
+    rewrite_request_body(request_body)
+
     return InboxMessage(
         activity_id=str(row.get("id", "")),
         text=_extract_text(request_body, row.get("summary")),
@@ -532,11 +550,34 @@ def _poll_once(
     if cursor is None:
         rows = list(reversed(rows))
 
+    # Imported lazily at use-site so a runtime that never sees an
+    # upload-receive row never imports the module. Cheap on the hot
+    # path because Python caches the import.
+    from inbox_uploads import is_chat_upload_row, fetch_and_stage
+
     new_count = 0
     last_id: str | None = None
     for row in rows:
         if not isinstance(row, dict):
             continue
+        if is_chat_upload_row(row):
+            # Side-effect row from the platform's poll-mode chat-upload
+            # handler — fetch the bytes, stage to /workspace/.molecule/
+            # chat-uploads, ack. NOT enqueued as an InboxMessage; the
+            # agent will see the chat message that REFERENCES this
+            # upload via a separate (later) activity row, with the
+            # pending: URI rewritten to a workspace: URI by
+            # message_from_activity. We DO advance the cursor past
+            # this row so a permanent network outage on /content
+            # doesn't stall the cursor and block real chat traffic.
+            fetch_and_stage(
+                row,
+                platform_url=platform_url,
+                workspace_id=workspace_id,
+                headers=headers,
+            )
+            last_id = str(row.get("id", "")) or last_id
+            continue
         if _is_self_notify_row(row):
             # The workspace-server's `/notify` handler writes the agent's
             # own send_message_to_user POSTs to activity_logs with
diff --git a/workspace/inbox_uploads.py b/workspace/inbox_uploads.py
new file mode 100644
index 00000000..798f18de
--- /dev/null
+++ b/workspace/inbox_uploads.py
@@ -0,0 +1,475 @@
+"""Poll-mode chat-upload fetcher + URI cache for the standalone path.
+
+Companion to ``inbox.py``. When the workspace's inbox poller sees an
+``activity_logs`` row with ``method='chat_upload_receive'`` (written by
+the platform's ``uploadPollMode`` handler — workspace-server
+``internal/handlers/chat_files.go``), this module:
+
+    1. Pulls the bytes from
+       ``GET /workspaces/:id/pending-uploads/:file_id/content``.
+    2. Writes them to ``/workspace/.molecule/chat-uploads/<prefix>-<name>``
+       — same on-disk shape as the push-mode handler in
+       ``internal_chat_uploads.py``, so anything downstream that already
+       resolves ``workspace:/workspace/.molecule/chat-uploads/...`` URIs
+       works unchanged.
+    3. POSTs ``/workspaces/:id/pending-uploads/:file_id/ack`` so Phase 3
+       sweep can clean up the platform-side ``pending_uploads`` row.
+    4. Records a ``platform-pending:<wsid>/<file_id> →
+       workspace:/workspace/.molecule/chat-uploads/...`` mapping in a
+       process-local cache so the chat message that arrives later
+       (referencing the platform-pending URI) gets rewritten before the
+       agent sees it.
+
+URI rewrite ordering — the chat message containing the
+``platform-pending:`` URI is logged by the platform AFTER the
+``chat_upload_receive`` row, so the inbox poller sees the upload-receive
+row first (lower activity_logs.id) and stages the bytes before the chat
+message arrives in the same poll batch (or a later one). The URI cache
+is therefore populated before the message_from_activity path needs it.
+A miss (network race, restart with stale cursor) is handled by keeping
+the original ``platform-pending:`` URI in the rewritten body — the agent
+will see something it can't open, which is preferable to silently
+dropping the URI.
+
+Auth — same Bearer token the inbox poller uses (``platform_auth.auth_headers``).
+Both endpoints are on the wsAuth-gated route, so this module can never
+read another tenant's bytes even if a token is misrouted.
+"""
+from __future__ import annotations
+
+import logging
+import mimetypes
+import os
+import re
+import secrets as pysecrets
+import threading
+from collections import OrderedDict
+from pathlib import Path
+from typing import Any
+
+logger = logging.getLogger(__name__)
+
+# Same on-disk root as internal_chat_uploads.CHAT_UPLOAD_DIR — keeping
+# these decoupled would let drift sneak in. Imported here rather than
+# from internal_chat_uploads to avoid pulling in starlette as a
+# transitive dep (this module runs in the standalone MCP path which
+# doesn't ship the in-container HTTP server).
+CHAT_UPLOAD_DIR = "/workspace/.molecule/chat-uploads"
+
+# Per-file safety net. The platform enforces 25 MB on the staging side,
+# but a buggy or hostile platform response shouldn't be able to fill the
+# workspace's disk — refuse to write more than this even if the response
+# claims a larger Content-Length.
+MAX_FILE_BYTES = 25 * 1024 * 1024
+
+# Network deadline for the GET. Tuned for a 25 MB transfer over a
+# reasonable consumer link (~5 Mbps gives ~40s for the full payload),
+# plus headroom for TLS + platform auth. Aligned with inbox poller's
+# 10s default for /activity calls — both are user-perceived latency.
+DEFAULT_FETCH_TIMEOUT = 60.0
+
+# Cap on the URI cache. A long-lived workspace handling thousands of
+# uploads shouldn't grow without bound; an LRU cap of 1024 keeps the
+# entries-needed-for-a-typical-conversation well within memory.
+URI_CACHE_MAX_ENTRIES = 1024
+
+# Same character class as internal_chat_uploads — kept duplicated rather
+# than imported to avoid dragging starlette into the standalone path.
+_UNSAFE_FILENAME_CHARS = re.compile(r"[^a-zA-Z0-9._\-]")
+
+
+def sanitize_filename(name: str) -> str:
+    """Reduce a user-supplied filename to a safe form.
+
+    Mirrors ``internal_chat_uploads.sanitize_filename`` and the Go
+    handler's ``SanitizeFilename`` — three-way parity is pinned by
+    ``workspace-server/internal/handlers/sanitize_filename_test.go`` and
+    ``workspace/tests/test_internal_chat_uploads.py`` so the URI shape
+    is identical regardless of which path handles the upload.
+    """
+    base = os.path.basename(name)
+    base = base.replace(" ", "_")
+    base = _UNSAFE_FILENAME_CHARS.sub("_", base)
+    if len(base) > 100:
+        ext = ""
+        dot = base.rfind(".")
+        if dot >= 0 and len(base) - dot <= 16:
+            ext = base[dot:]
+        base = base[: 100 - len(ext)] + ext
+    if base in ("", ".", ".."):
+        return "file"
+    return base
+
+
+# ---------------------------------------------------------------------------
+# URI cache — maps platform-pending URIs to local workspace: URIs
+# ---------------------------------------------------------------------------
+
+
+class _URICache:
+    """Thread-safe bounded LRU mapping of platform-pending → workspace URIs.
+
+    Bounded so a workspace that runs for months and handles thousands of
+    uploads doesn't accumulate entries forever. ``OrderedDict.move_to_end``
+    promotes recently-used entries; eviction takes the oldest.
+
+    The cache is intentionally per-process — there is no persistence
+    across a workspace restart. A restart with a stale inbox cursor that
+    re-poll an upload-receive row will re-fetch (the bytes are already
+    on disk from the prior session — see ``stage_to_disk``'s O_EXCL
+    handling) and re-register; a chat message that referenced the
+    platform-pending URI BEFORE the restart and arrives AFTER would miss
+    the rewrite and surface the platform-pending URI to the agent. That
+    is preferable to a stale persisted mapping that points at a deleted
+    file.
+    """
+
+    def __init__(self, max_entries: int = URI_CACHE_MAX_ENTRIES):
+        self._max = max_entries
+        self._lock = threading.Lock()
+        self._entries: "OrderedDict[str, str]" = OrderedDict()
+
+    def get(self, pending_uri: str) -> str | None:
+        with self._lock:
+            local = self._entries.get(pending_uri)
+            if local is not None:
+                self._entries.move_to_end(pending_uri)
+            return local
+
+    def set(self, pending_uri: str, local_uri: str) -> None:
+        with self._lock:
+            self._entries[pending_uri] = local_uri
+            self._entries.move_to_end(pending_uri)
+            while len(self._entries) > self._max:
+                self._entries.popitem(last=False)
+
+    def __len__(self) -> int:
+        with self._lock:
+            return len(self._entries)
+
+    def clear(self) -> None:
+        with self._lock:
+            self._entries.clear()
+
+
+_cache = _URICache()
+
+
+def get_cache() -> _URICache:
+    """Expose the module-singleton cache for tests and the rewrite path."""
+    return _cache
+
+
+def resolve_pending_uri(uri: str) -> str | None:
+    """Return the local ``workspace:`` URI for a ``platform-pending:`` URI,
+    or None if not yet staged. Convenience for callers that want to
+    fall back to an on-demand fetch — pass the result through to
+    ``executor_helpers.resolve_attachment_uri``.
+    """
+    return _cache.get(uri)
+
+
+# ---------------------------------------------------------------------------
+# On-disk staging
+# ---------------------------------------------------------------------------
+
+
+def _open_safe(path: str) -> int:
+    """Open ``path`` for write with ``O_CREAT|O_EXCL|O_NOFOLLOW``.
+
+    Same shape as ``internal_chat_uploads._open_safe`` — refuses to
+    follow a pre-existing symlink at the target and refuses to overwrite
+    an existing regular file. The 16-byte random prefix makes a name
+    collision astronomical, but defense-in-depth costs nothing.
+    """
+    flags = os.O_WRONLY | os.O_CREAT | os.O_EXCL
+    if hasattr(os, "O_NOFOLLOW"):
+        flags |= os.O_NOFOLLOW
+    return os.open(path, flags, 0o600)
+
+
+def stage_to_disk(content: bytes, filename: str) -> str:
+    """Write ``content`` under ``CHAT_UPLOAD_DIR`` and return the local URI.
+
+    Returns ``workspace:/workspace/.molecule/chat-uploads/<prefix>-<sanitized>``.
+    The 32-hex prefix makes the on-disk name unguessable to anything
+    that didn't see the response, so even if a stale agent has a guess
+    at the original filename it can't construct a URL to a sibling's
+    upload.
+
+    Raises:
+        OSError: write failure (mkdir, open, or write). Caller is
+            expected to log + skip; the activity row stays unacked so a
+            future poll re-tries.
+        ValueError: ``content`` exceeds ``MAX_FILE_BYTES``. Pre-staging
+            guard belt-and-braces above the platform's same-side cap.
+    """
+    if len(content) > MAX_FILE_BYTES:
+        raise ValueError(
+            f"content size {len(content)} exceeds workspace cap {MAX_FILE_BYTES}"
+        )
+
+    Path(CHAT_UPLOAD_DIR).mkdir(parents=True, exist_ok=True)
+
+    sanitized = sanitize_filename(filename)
+    prefix = pysecrets.token_hex(16)
+    stored = f"{prefix}-{sanitized}"
+    target = os.path.join(CHAT_UPLOAD_DIR, stored)
+
+    fd = _open_safe(target)
+    try:
+        with os.fdopen(fd, "wb") as f:
+            f.write(content)
+    except OSError:
+        # Best-effort cleanup — partial writes leave a stub file that
+        # would mask a future retry's success otherwise.
+        try:
+            os.unlink(target)
+        except OSError:
+            pass
+        raise
+
+    return f"workspace:{CHAT_UPLOAD_DIR}/{stored}"
+
+
+# ---------------------------------------------------------------------------
+# Activity row → fetch/stage/ack flow
+# ---------------------------------------------------------------------------
+
+
+def _request_body_dict(row: dict[str, Any]) -> dict[str, Any] | None:
+    """Coerce ``row['request_body']`` into a dict.
+
+    The /activity API returns request_body as JSON (already-deserialized
+    by httpx). Some legacy paths or mocked transports may emit a string;
+    handle defensively rather than raising.
+    """
+    body = row.get("request_body")
+    if isinstance(body, dict):
+        return body
+    if isinstance(body, str):
+        import json
+        try:
+            decoded = json.loads(body)
+        except (TypeError, ValueError):
+            return None
+        return decoded if isinstance(decoded, dict) else None
+    return None
+
+
+def is_chat_upload_row(row: dict[str, Any]) -> bool:
+    """True if ``row`` is the platform's chat-upload-receive activity.
+
+    Used by the inbox poller to fork the row off the regular A2A
+    message handling path — this row is not a peer message; it's an
+    instruction to fetch + stage bytes. Match on ``method`` only;
+    ``activity_type`` is already filtered to ``a2a_receive`` upstream.
+    """
+    return row.get("method") == "chat_upload_receive"
+
+
+def fetch_and_stage(
+    row: dict[str, Any],
+    *,
+    platform_url: str,
+    workspace_id: str,
+    headers: dict[str, str],
+    timeout_secs: float = DEFAULT_FETCH_TIMEOUT,
+) -> str | None:
+    """Fetch the row's bytes, stage them under chat-uploads, and ack.
+
+    Returns the local ``workspace:`` URI on success, or ``None`` if any
+    step failed (logged with enough detail to triage). Failure leaves
+    the platform-side row unacked, so a subsequent poll retries — the
+    activity row stays in the cursor's window because we DO advance the
+    cursor (the row is "handled" from the inbox's perspective even on
+    fetch failure; otherwise a permanent network outage would stall the
+    cursor and block real chat traffic).
+
+    On success, the URI cache is updated so a subsequent chat message
+    referencing the same ``platform-pending:`` URI is rewritten before
+    the agent sees it.
+    """
+    body = _request_body_dict(row)
+    if body is None:
+        logger.warning(
+            "inbox_uploads: row %s missing request_body; cannot fetch",
+            row.get("id"),
+        )
+        return None
+
+    file_id = body.get("file_id")
+    if not isinstance(file_id, str) or not file_id:
+        logger.warning(
+            "inbox_uploads: row %s has no file_id in request_body",
+            row.get("id"),
+        )
+        return None
+
+    pending_uri = body.get("uri")
+    if not isinstance(pending_uri, str) or not pending_uri:
+        # Reconstruct what the platform would have written — defensive
+        # against a row whose uri field got truncated. Same shape as the
+        # Go handler's URI builder.
+        pending_uri = f"platform-pending:{workspace_id}/{file_id}"
+
+    filename = body.get("name") or "file"
+    if not isinstance(filename, str):
+        filename = "file"
+
+    # Lazy httpx import: the standalone MCP path uses httpx; an in-
+    # container caller that imports this module by accident shouldn't
+    # explode at import time.
+    try:
+        import httpx  # noqa: WPS433
+    except ImportError:
+        logger.error("inbox_uploads: httpx not installed; cannot fetch %s", file_id)
+        return None
+
+    content_url = f"{platform_url}/workspaces/{workspace_id}/pending-uploads/{file_id}/content"
+    ack_url = f"{platform_url}/workspaces/{workspace_id}/pending-uploads/{file_id}/ack"
+
+    try:
+        with httpx.Client(timeout=timeout_secs) as client:
+            resp = client.get(content_url, headers=headers)
+    except Exception as exc:  # noqa: BLE001
+        logger.warning(
+            "inbox_uploads: GET %s failed: %s", content_url, exc
+        )
+        return None
+
+    if resp.status_code == 404:
+        # Row was swept or already acked by a previous poll race — nothing
+        # to fetch. Don't ack again; the platform's GC handles it. This is
+        # a soft-skip, not an error — log at INFO so triage isn't noisy.
+        logger.info(
+            "inbox_uploads: pending upload %s already gone (404); skipping",
+            file_id,
+        )
+        return None
+    if resp.status_code >= 400:
+        logger.warning(
+            "inbox_uploads: GET %s returned %d: %s",
+            content_url,
+            resp.status_code,
+            (resp.text or "")[:200],
+        )
+        return None
+
+    content = resp.content or b""
+    if len(content) > MAX_FILE_BYTES:
+        logger.warning(
+            "inbox_uploads: refusing to stage %s — size %d exceeds cap %d",
+            file_id,
+            len(content),
+            MAX_FILE_BYTES,
+        )
+        return None
+
+    # Mimetype precedence: platform's Content-Type header → request_body
+    # mimeType field → extension guess. Same precedence as the in-
+    # container ingest handler.
+    mime_header = resp.headers.get("content-type", "").split(";")[0].strip()
+    mime = (
+        mime_header
+        or (body.get("mimeType") if isinstance(body.get("mimeType"), str) else "")
+        or (mimetypes.guess_type(filename)[0] or "")
+    )
+
+    try:
+        local_uri = stage_to_disk(content, filename)
+    except (OSError, ValueError) as exc:
+        logger.error(
+            "inbox_uploads: failed to stage %s (%s) to disk: %s",
+            file_id,
+            filename,
+            exc,
+        )
+        return None
+
+    _cache.set(pending_uri, local_uri)
+    logger.info(
+        "inbox_uploads: staged file_id=%s name=%s size=%d mime=%s pending_uri=%s local_uri=%s",
+        file_id,
+        filename,
+        len(content),
+        mime,
+        pending_uri,
+        local_uri,
+    )
+
+    # Ack last so a write failure above leaves the row available for a
+    # retry on the next poll. A failed ack is logged but doesn't roll
+    # back the on-disk file — the platform's sweep will clean up
+    # eventually.
+    try:
+        with httpx.Client(timeout=timeout_secs) as client:
+            ack_resp = client.post(ack_url, headers=headers)
+        if ack_resp.status_code >= 400:
+            logger.warning(
+                "inbox_uploads: ack %s returned %d: %s",
+                ack_url,
+                ack_resp.status_code,
+                (ack_resp.text or "")[:200],
+            )
+    except Exception as exc:  # noqa: BLE001
+        logger.warning("inbox_uploads: POST %s failed: %s", ack_url, exc)
+
+    return local_uri
+
+
+# ---------------------------------------------------------------------------
+# URI rewrite for incoming chat messages
+# ---------------------------------------------------------------------------
+#
+# The chat message that references a staged upload arrives as a
+# SEPARATE activity_log row, with parts of kind=file containing
+# platform-pending: URIs in the file.uri field. Walk the structure
+# in-place and rewrite to the local workspace: URI when the cache has it.
+# Unknown URIs pass through unchanged — the agent gets to choose how
+# to react (most runtimes log + ignore an unresolvable URI).
+
+
+def _rewrite_part(part: Any) -> None:
+    """Mutate a single A2A Part dict to swap platform-pending: URIs."""
+    if not isinstance(part, dict):
+        return
+    file_obj = part.get("file")
+    if not isinstance(file_obj, dict):
+        return
+    uri = file_obj.get("uri")
+    if not isinstance(uri, str) or not uri.startswith("platform-pending:"):
+        return
+    rewritten = _cache.get(uri)
+    if rewritten:
+        file_obj["uri"] = rewritten
+
+
+def rewrite_request_body(body: Any) -> None:
+    """Mutate ``body`` in-place, replacing platform-pending: URIs with
+    the cached local equivalents.
+
+    Walks the same shapes ``inbox._extract_text`` accepts:
+
+      - ``body['parts']``
+      - ``body['params']['parts']``
+      - ``body['params']['message']['parts']``
+
+    No-op for shapes that don't match — the message simply passes
+    through to the agent as-is.
+    """
+    if not isinstance(body, dict):
+        return
+    candidates: list[Any] = []
+    params = body.get("params") if isinstance(body.get("params"), dict) else None
+    if params:
+        message = params.get("message") if isinstance(params.get("message"), dict) else None
+        if message:
+            candidates.append(message.get("parts"))
+        candidates.append(params.get("parts"))
+    candidates.append(body.get("parts"))
+
+    for parts in candidates:
+        if isinstance(parts, list):
+            for part in parts:
+                _rewrite_part(part)
diff --git a/workspace/tests/test_inbox.py b/workspace/tests/test_inbox.py
index 6731701a..162c32c2 100644
--- a/workspace/tests/test_inbox.py
+++ b/workspace/tests/test_inbox.py
@@ -701,3 +701,165 @@ def test_set_notification_callback_none_clears(state: inbox.InboxState):
     state.record(_msg("act-1"))
 
     assert received == []
+
+
+# ---------------------------------------------------------------------------
+# Phase 2 — chat_upload_receive rows route to inbox_uploads.fetch_and_stage
+# ---------------------------------------------------------------------------
+
+
+def test_poll_once_skips_chat_upload_row_from_queue(state: inbox.InboxState, monkeypatch, tmp_path):
+    """A row with method='chat_upload_receive' must NOT enqueue as a
+    chat message — it's a side-effect telling the workspace to fetch
+    bytes. Pin the contract so a refactor that flattens the row loop
+    can't silently re-enqueue these as 'empty A2A message' rows."""
+    import inbox_uploads
+    monkeypatch.setattr(inbox_uploads, "CHAT_UPLOAD_DIR", str(tmp_path / "chat-uploads"))
+    inbox_uploads.get_cache().clear()
+
+    rows = [
+        {
+            "id": "act-1",
+            "source_id": None,
+            "method": "chat_upload_receive",
+            "summary": "chat_upload_receive: foo.pdf",
+            "request_body": {
+                "file_id": "abc123",
+                "name": "foo.pdf",
+                "mimeType": "application/pdf",
+                "size": 4,
+                "uri": "platform-pending:ws-1/abc123",
+            },
+            "created_at": "2026-05-04T10:00:00Z",
+        },
+    ]
+    resp = _make_response(200, rows)
+    p, _ = _patch_httpx(resp)
+    fetch_called = []
+
+    def fake_fetch(row, **kwargs):
+        fetch_called.append((row.get("id"), kwargs["workspace_id"]))
+        return "workspace:/local/foo.pdf"
+
+    with p, patch.object(inbox_uploads, "fetch_and_stage", fake_fetch):
+        n = inbox._poll_once(state, "http://platform", "ws-1", {})
+
+    # Not enqueued + cursor advanced.
+    assert n == 0
+    assert state.peek(10) == []
+    assert state.load_cursor() == "act-1"
+    # fetch_and_stage was invoked with the row and workspace_id.
+    assert fetch_called == [("act-1", "ws-1")]
+
+
+def test_poll_once_chat_upload_row_then_chat_message_rewrites_uri(state: inbox.InboxState, monkeypatch, tmp_path):
+    """The classic ordering: upload-receive row first (lower id), chat
+    message referencing platform-pending: URI second. The chat message
+    that lands in the inbox must have its URI rewritten to the local
+    workspace: URI before the agent sees it.
+    """
+    import inbox_uploads
+    monkeypatch.setattr(inbox_uploads, "CHAT_UPLOAD_DIR", str(tmp_path / "chat-uploads"))
+    cache = inbox_uploads.get_cache()
+    cache.clear()
+
+    # Pretend the fetch already populated the cache. (The real flow
+    # populates it inside fetch_and_stage; we patch that to keep the
+    # test focused on the rewrite contract.)
+    cache.set("platform-pending:ws-1/abc123", "workspace:/workspace/.molecule/chat-uploads/xx-foo.pdf")
+
+    rows = [
+        {
+            "id": "act-1",
+            "source_id": None,
+            "method": "chat_upload_receive",
+            "summary": "chat_upload_receive: foo.pdf",
+            "request_body": {
+                "file_id": "abc123",
+                "name": "foo.pdf",
+                "mimeType": "application/pdf",
+                "size": 4,
+                "uri": "platform-pending:ws-1/abc123",
+            },
+            "created_at": "2026-05-04T10:00:00Z",
+        },
+        {
+            "id": "act-2",
+            "source_id": None,
+            "method": "message/send",
+            "summary": None,
+            "request_body": {
+                "params": {
+                    "message": {
+                        "parts": [
+                            {"kind": "text", "text": "look at this"},
+                            {
+                                "kind": "file",
+                                "file": {
+                                    "uri": "platform-pending:ws-1/abc123",
+                                    "name": "foo.pdf",
+                                },
+                            },
+                        ]
+                    }
+                }
+            },
+            "created_at": "2026-05-04T10:00:01Z",
+        },
+    ]
+    resp = _make_response(200, rows)
+    p, _ = _patch_httpx(resp)
+
+    def fake_fetch(row, **kwargs):
+        return "workspace:/workspace/.molecule/chat-uploads/xx-foo.pdf"
+
+    with p, patch.object(inbox_uploads, "fetch_and_stage", fake_fetch):
+        n = inbox._poll_once(state, "http://platform", "ws-1", {})
+
+    # Only the chat message is enqueued.
+    assert n == 1
+    queue = state.peek(10)
+    assert len(queue) == 1
+    msg = queue[0]
+    assert msg.activity_id == "act-2"
+    # The URI in the row's request_body was mutated by message_from_activity
+    # → rewrite_request_body. Re-extracting reveals the rewritten value.
+    rewritten = rows[1]["request_body"]["params"]["message"]["parts"][1]["file"]["uri"]
+    assert rewritten == "workspace:/workspace/.molecule/chat-uploads/xx-foo.pdf"
+
+
+def test_poll_once_chat_upload_row_advances_cursor_even_on_fetch_failure(
+    state: inbox.InboxState, monkeypatch, tmp_path
+):
+    """A permanent network failure on /content must NOT stall the cursor
+    — otherwise one bad upload blocks all real chat traffic for the
+    workspace. fetch_and_stage returns None on failure, but the row is
+    still considered handled from the cursor's perspective."""
+    import inbox_uploads
+    monkeypatch.setattr(inbox_uploads, "CHAT_UPLOAD_DIR", str(tmp_path / "chat-uploads"))
+
+    rows = [
+        {
+            "id": "act-broken",
+            "source_id": None,
+            "method": "chat_upload_receive",
+            "summary": "chat_upload_receive: doomed.pdf",
+            "request_body": {
+                "file_id": "doom",
+                "name": "doomed.pdf",
+                "uri": "platform-pending:ws-1/doom",
+            },
+            "created_at": "2026-05-04T10:00:00Z",
+        },
+    ]
+    resp = _make_response(200, rows)
+    p, _ = _patch_httpx(resp)
+
+    def fake_fetch(row, **kwargs):
+        return None  # network failure
+
+    with p, patch.object(inbox_uploads, "fetch_and_stage", fake_fetch):
+        inbox._poll_once(state, "http://platform", "ws-1", {})
+
+    assert state.peek(10) == []
+    assert state.load_cursor() == "act-broken"
diff --git a/workspace/tests/test_inbox_uploads.py b/workspace/tests/test_inbox_uploads.py
new file mode 100644
index 00000000..515616e2
--- /dev/null
+++ b/workspace/tests/test_inbox_uploads.py
@@ -0,0 +1,697 @@
+"""Tests for workspace/inbox_uploads.py — poll-mode chat-upload fetcher.
+
+Covers the full activity-row → fetch → stage-on-disk → ack flow plus
+the URI cache and the rewrite that swaps platform-pending: URIs to
+local workspace: URIs in subsequent chat messages.
+"""
+from __future__ import annotations
+
+import os
+from typing import Any
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+import inbox_uploads
+
+
+@pytest.fixture(autouse=True)
+def _reset_cache_and_dir(tmp_path, monkeypatch):
+    """Each test starts with an empty URI cache and a temp upload dir
+    so on-disk artifacts from one test don't leak into the next."""
+    inbox_uploads.get_cache().clear()
+    monkeypatch.setattr(inbox_uploads, "CHAT_UPLOAD_DIR", str(tmp_path / "chat-uploads"))
+    yield
+    inbox_uploads.get_cache().clear()
+
+
+# ---------------------------------------------------------------------------
+# sanitize_filename — parity with internal_chat_uploads + Go SanitizeFilename
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "raw,want",
+    [
+        ("../../etc/passwd", "passwd"),
+        ("/etc/passwd", "passwd"),
+        ("hello world.pdf", "hello_world.pdf"),
+        ("weird;chars!?.txt", "weird_chars__.txt"),
+        ("中文.docx", "__.docx"),
+        ("file (1).pdf", "file__1_.pdf"),
+        ("report-2026.05.04_v2.pdf", "report-2026.05.04_v2.pdf"),
+        ("", "file"),
+        (".", "file"),
+        ("..", "file"),
+    ],
+)
+def test_sanitize_filename_parity_with_python_internal(raw, want):
+    assert inbox_uploads.sanitize_filename(raw) == want
+
+
+def test_sanitize_filename_caps_at_100_preserves_short_extension():
+    long = "a" * 200 + ".pdf"
+    got = inbox_uploads.sanitize_filename(long)
+    assert len(got) == 100
+    assert got.endswith(".pdf")
+
+
+def test_sanitize_filename_drops_long_extension():
+    long = "c" * 90 + ".thisisaverylongextensionnotpreserved"
+    got = inbox_uploads.sanitize_filename(long)
+    assert len(got) == 100
+    assert ".thisisaverylongextensionnotpreserved" not in got
+
+
+# ---------------------------------------------------------------------------
+# _URICache — LRU semantics
+# ---------------------------------------------------------------------------
+
+
+def test_uricache_set_get_roundtrip():
+    c = inbox_uploads._URICache(max_entries=10)
+    c.set("platform-pending:ws/1", "workspace:/local/1")
+    assert c.get("platform-pending:ws/1") == "workspace:/local/1"
+
+
+def test_uricache_get_missing_returns_none():
+    c = inbox_uploads._URICache(max_entries=10)
+    assert c.get("platform-pending:ws/missing") is None
+
+
+def test_uricache_evicts_oldest_at_capacity():
+    c = inbox_uploads._URICache(max_entries=2)
+    c.set("a", "A")
+    c.set("b", "B")
+    c.set("c", "C")  # evicts "a"
+    assert c.get("a") is None
+    assert c.get("b") == "B"
+    assert c.get("c") == "C"
+    assert len(c) == 2
+
+
+def test_uricache_get_promotes_recently_used():
+    c = inbox_uploads._URICache(max_entries=2)
+    c.set("a", "A")
+    c.set("b", "B")
+    # Promote "a" by reading; next set should evict "b" instead of "a".
+    assert c.get("a") == "A"
+    c.set("c", "C")
+    assert c.get("a") == "A"
+    assert c.get("b") is None
+    assert c.get("c") == "C"
+
+
+def test_uricache_overwrite_updates_value():
+    c = inbox_uploads._URICache(max_entries=10)
+    c.set("k", "v1")
+    c.set("k", "v2")
+    assert c.get("k") == "v2"
+    assert len(c) == 1
+
+
+def test_uricache_clear():
+    c = inbox_uploads._URICache(max_entries=10)
+    c.set("a", "A")
+    c.set("b", "B")
+    c.clear()
+    assert c.get("a") is None
+    assert len(c) == 0
+
+
+def test_resolve_pending_uri_uses_module_cache():
+    inbox_uploads.get_cache().set("platform-pending:ws/x", "workspace:/local/x")
+    assert inbox_uploads.resolve_pending_uri("platform-pending:ws/x") == "workspace:/local/x"
+    assert inbox_uploads.resolve_pending_uri("platform-pending:ws/missing") is None
+
+
+# ---------------------------------------------------------------------------
+# stage_to_disk
+# ---------------------------------------------------------------------------
+
+
+def test_stage_to_disk_writes_file_and_returns_workspace_uri(tmp_path):
+    uri = inbox_uploads.stage_to_disk(b"hello", "report.pdf")
+    assert uri.startswith("workspace:")
+    path = uri[len("workspace:"):]
+    assert os.path.isfile(path)
+    with open(path, "rb") as f:
+        assert f.read() == b"hello"
+    assert path.endswith("-report.pdf")
+    # Prefix is 32 hex chars + "-" + name.
+    name = os.path.basename(path)
+    prefix, _, _ = name.partition("-")
+    assert len(prefix) == 32
+
+
+def test_stage_to_disk_sanitizes_filename():
+    uri = inbox_uploads.stage_to_disk(b"x", "../../evil.txt")
+    name = os.path.basename(uri)
+    assert "/" not in name
+    assert name.endswith("-evil.txt")
+
+
+def test_stage_to_disk_rejects_oversize():
+    with pytest.raises(ValueError):
+        inbox_uploads.stage_to_disk(b"x" * (inbox_uploads.MAX_FILE_BYTES + 1), "big.bin")
+
+
+def test_stage_to_disk_creates_directory_if_missing():
+    # CHAT_UPLOAD_DIR is monkeypatched to a non-existent tmp path; the
+    # call must mkdir -p it on first write.
+    assert not os.path.exists(inbox_uploads.CHAT_UPLOAD_DIR)
+    inbox_uploads.stage_to_disk(b"x", "a.txt")
+    assert os.path.isdir(inbox_uploads.CHAT_UPLOAD_DIR)
+
+
+def test_stage_to_disk_write_failure_cleans_partial_file(tmp_path, monkeypatch):
+    # open() succeeds but write() fails — the partial file must be
+    # removed so a retry can claim a fresh prefix without colliding.
+    real_fdopen = os.fdopen
+    written_paths: list[str] = []
+
+    def boom_fdopen(fd, mode):
+        # Wrap the real file with one whose write() raises.
+        f = real_fdopen(fd, mode)
+        # Track which path's fd we opened by inspecting the chat-upload dir.
+        for entry in os.listdir(inbox_uploads.CHAT_UPLOAD_DIR):
+            written_paths.append(os.path.join(inbox_uploads.CHAT_UPLOAD_DIR, entry))
+        original_write = f.write
+
+        def bad_write(b):
+            original_write(b"")  # ensure file exists
+            raise OSError(28, "no space")
+        f.write = bad_write
+        return f
+
+    monkeypatch.setattr(os, "fdopen", boom_fdopen)
+    with pytest.raises(OSError):
+        inbox_uploads.stage_to_disk(b"data", "x.txt")
+    # All staged files cleaned up.
+    for p in written_paths:
+        assert not os.path.exists(p)
+
+
+def test_stage_to_disk_write_failure_unlink_failure_swallowed(monkeypatch):
+    # open() succeeds, write() fails, unlink() ALSO fails — the unlink
+    # error is swallowed and the original write error propagates.
+    real_fdopen = os.fdopen
+
+    def boom_fdopen(fd, mode):
+        f = real_fdopen(fd, mode)
+
+        def bad_write(_):
+            raise OSError(28, "no space")
+        f.write = bad_write
+        return f
+
+    def bad_unlink(_):
+        raise OSError(13, "permission denied")
+
+    monkeypatch.setattr(os, "fdopen", boom_fdopen)
+    monkeypatch.setattr(os, "unlink", bad_unlink)
+    with pytest.raises(OSError) as ei:
+        inbox_uploads.stage_to_disk(b"data", "x.txt")
+    # Original write error, not the unlink error.
+    assert ei.value.errno == 28
+
+
+def test_stage_to_disk_propagates_oserror_and_cleans_partial(tmp_path, monkeypatch):
+    # Make the dir read-only AFTER mkdir succeeds, so open() fails. Skip
+    # this on platforms where the dir's permissions don't restrict the
+    # process owner (root in Docker, etc.).
+    inbox_uploads.stage_to_disk(b"first", "a.txt")
+    if os.geteuid() == 0:
+        pytest.skip("root bypasses permission bits")
+    os.chmod(inbox_uploads.CHAT_UPLOAD_DIR, 0o500)
+    try:
+        with pytest.raises(OSError):
+            inbox_uploads.stage_to_disk(b"second", "b.txt")
+    finally:
+        os.chmod(inbox_uploads.CHAT_UPLOAD_DIR, 0o755)
+
+
+# ---------------------------------------------------------------------------
+# is_chat_upload_row + _request_body_dict
+# ---------------------------------------------------------------------------
+
+
+def test_is_chat_upload_row_true_on_method_match():
+    assert inbox_uploads.is_chat_upload_row({"method": "chat_upload_receive"})
+
+
+def test_is_chat_upload_row_false_on_other_methods():
+    assert not inbox_uploads.is_chat_upload_row({"method": "message/send"})
+    assert not inbox_uploads.is_chat_upload_row({"method": None})
+    assert not inbox_uploads.is_chat_upload_row({})
+
+
+def test_request_body_dict_passthrough():
+    body = {"file_id": "x"}
+    assert inbox_uploads._request_body_dict({"request_body": body}) is body
+
+
+def test_request_body_dict_string_decoded():
+    assert inbox_uploads._request_body_dict({"request_body": '{"a": 1}'}) == {"a": 1}
+
+
+def test_request_body_dict_invalid_string_returns_none():
+    assert inbox_uploads._request_body_dict({"request_body": "not json"}) is None
+
+
+def test_request_body_dict_non_dict_after_decode_returns_none():
+    assert inbox_uploads._request_body_dict({"request_body": "[1, 2]"}) is None
+
+
+def test_request_body_dict_other_type_returns_none():
+    assert inbox_uploads._request_body_dict({"request_body": 123}) is None
+
+
+# ---------------------------------------------------------------------------
+# fetch_and_stage — the full GET / write / ack flow
+# ---------------------------------------------------------------------------
+
+
+def _make_resp(status_code: int, content: bytes = b"", content_type: str = "", text: str = "") -> MagicMock:
+    resp = MagicMock()
+    resp.status_code = status_code
+    resp.content = content
+    headers: dict[str, str] = {}
+    if content_type:
+        headers["content-type"] = content_type
+    resp.headers = headers
+    resp.text = text
+    return resp
+
+
+def _patch_httpx_for_fetch(get_resp: MagicMock, ack_resp: MagicMock | None = None):
+    """Patch httpx.Client so each new context-manager returns a client
+    whose .get() returns get_resp and .post() returns ack_resp.
+    """
+    client = MagicMock()
+    client.__enter__ = MagicMock(return_value=client)
+    client.__exit__ = MagicMock(return_value=False)
+    client.get = MagicMock(return_value=get_resp)
+    client.post = MagicMock(return_value=ack_resp or _make_resp(200))
+    return patch("httpx.Client", return_value=client), client
+
+
+def _row(file_id: str = "file-1", uri: str | None = None, name: str = "report.pdf", body_extra: dict | None = None) -> dict:
+    body: dict[str, Any] = {
+        "file_id": file_id,
+        "name": name,
+        "mimeType": "application/pdf",
+        "size": 9,
+    }
+    if uri is not None:
+        body["uri"] = uri
+    if body_extra:
+        body.update(body_extra)
+    return {
+        "id": "act-100",
+        "source_id": None,
+        "method": "chat_upload_receive",
+        "summary": "chat_upload_receive: report.pdf",
+        "request_body": body,
+        "created_at": "2026-05-04T10:00:00Z",
+    }
+
+
+def test_fetch_and_stage_happy_path_writes_file_acks_and_caches():
+    pending_uri = "platform-pending:ws-1/file-1"
+    row = _row(uri=pending_uri)
+    get_resp = _make_resp(200, content=b"PDF-bytes", content_type="application/pdf")
+    p, client = _patch_httpx_for_fetch(get_resp)
+    with p:
+        local_uri = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={"Authorization": "Bearer t"}
+        )
+    assert local_uri is not None
+    assert local_uri.startswith("workspace:")
+    # On-disk file content matches.
+    path = local_uri[len("workspace:"):]
+    with open(path, "rb") as f:
+        assert f.read() == b"PDF-bytes"
+    # Cache populated.
+    assert inbox_uploads.get_cache().get(pending_uri) == local_uri
+    # Ack POSTed to the right URL.
+    client.post.assert_called_once()
+    args, kwargs = client.post.call_args
+    assert "/pending-uploads/file-1/ack" in args[0]
+    assert kwargs["headers"]["Authorization"] == "Bearer t"
+
+
+def test_fetch_and_stage_reconstructs_uri_when_missing_in_body():
+    row = _row(uri=None)  # request_body has no 'uri'
+    get_resp = _make_resp(200, content=b"x", content_type="text/plain")
+    p, _ = _patch_httpx_for_fetch(get_resp)
+    with p:
+        inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    # Cache key reconstructed from workspace_id + file_id.
+    assert inbox_uploads.get_cache().get("platform-pending:ws-1/file-1") is not None
+
+
+def test_fetch_and_stage_returns_none_on_missing_request_body():
+    row = {"id": "act-100", "method": "chat_upload_receive"}
+    # No httpx call should happen, but we patch defensively.
+    p, client = _patch_httpx_for_fetch(_make_resp(200))
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    client.get.assert_not_called()
+
+
+def test_fetch_and_stage_returns_none_on_missing_file_id():
+    row = {"id": "act-100", "method": "chat_upload_receive", "request_body": {"name": "x.pdf"}}
+    p, client = _patch_httpx_for_fetch(_make_resp(200))
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    client.get.assert_not_called()
+
+
+def test_fetch_and_stage_handles_nonstring_file_id():
+    row = {"id": "act-100", "method": "chat_upload_receive", "request_body": {"file_id": 123}}
+    p, client = _patch_httpx_for_fetch(_make_resp(200))
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    client.get.assert_not_called()
+
+
+def test_fetch_and_stage_404_returns_none_no_ack():
+    row = _row()
+    get_resp = _make_resp(404, text="gone")
+    ack_resp = _make_resp(200)
+    p, client = _patch_httpx_for_fetch(get_resp, ack_resp)
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    # No ack — the row is already gone.
+    client.post.assert_not_called()
+
+
+def test_fetch_and_stage_500_returns_none_no_ack():
+    row = _row()
+    p, client = _patch_httpx_for_fetch(_make_resp(500, text="boom"))
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    client.post.assert_not_called()
+
+
+def test_fetch_and_stage_network_error_returns_none():
+    row = _row()
+    client = MagicMock()
+    client.__enter__ = MagicMock(return_value=client)
+    client.__exit__ = MagicMock(return_value=False)
+    client.get = MagicMock(side_effect=RuntimeError("connection refused"))
+    with patch("httpx.Client", return_value=client):
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+
+
+def test_fetch_and_stage_oversize_response_refused():
+    row = _row()
+    big = b"x" * (inbox_uploads.MAX_FILE_BYTES + 1)
+    p, client = _patch_httpx_for_fetch(_make_resp(200, content=big, content_type="application/octet-stream"))
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    client.post.assert_not_called()
+
+
+def test_fetch_and_stage_ack_failure_does_not_invalidate_local_uri():
+    row = _row(uri="platform-pending:ws-1/file-1")
+    get_resp = _make_resp(200, content=b"data", content_type="text/plain")
+    ack_resp = _make_resp(500, text="ack failed")
+    p, _ = _patch_httpx_for_fetch(get_resp, ack_resp)
+    with p:
+        local_uri = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    # On-disk staging succeeded; ack failure is logged but doesn't
+    # roll back the cache.
+    assert local_uri is not None
+    assert inbox_uploads.get_cache().get("platform-pending:ws-1/file-1") == local_uri
+
+
+def test_fetch_and_stage_ack_network_error_swallowed():
+    row = _row(uri="platform-pending:ws-1/file-1")
+    client = MagicMock()
+    client.__enter__ = MagicMock(return_value=client)
+    client.__exit__ = MagicMock(return_value=False)
+    client.get = MagicMock(return_value=_make_resp(200, content=b"data", content_type="text/plain"))
+    client.post = MagicMock(side_effect=RuntimeError("ack network error"))
+    with patch("httpx.Client", return_value=client):
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is not None  # GET succeeded → URI returned even if ack blew up
+
+
+def test_fetch_and_stage_uses_response_content_type_when_present():
+    row = _row(name="thing.bin", body_extra={"mimeType": "application/x-bogus"})
+    # Response says image/png; should win over body's mimeType.
+    get_resp = _make_resp(200, content=b"PNG", content_type="image/png; charset=binary")
+    p, _ = _patch_httpx_for_fetch(get_resp)
+    with p:
+        # We don't assert on returned mime (not part of the contract);
+        # the test just verifies the happy path runs without trying to
+        # parse the trailing parameter.
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is not None
+
+
+def test_fetch_and_stage_nonstring_filename_falls_back_to_file():
+    # body['name'] is a non-string (e.g. truncated to None or a number);
+    # filename must default to "file" so sanitize_filename has something
+    # to work with.
+    row = _row(body_extra={"name": 12345})
+    p, _ = _patch_httpx_for_fetch(_make_resp(200, content=b"x", content_type="text/plain"))
+    with p:
+        local_uri = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert local_uri is not None
+    assert local_uri.endswith("-file")
+
+
+def test_fetch_and_stage_default_filename_when_missing():
+    row = {
+        "id": "act",
+        "method": "chat_upload_receive",
+        "request_body": {"file_id": "file-1"},
+    }
+    p, _ = _patch_httpx_for_fetch(_make_resp(200, content=b"data", content_type="text/plain"))
+    with p:
+        local_uri = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert local_uri is not None
+    assert local_uri.endswith("-file")  # default filename
+
+
+def test_fetch_and_stage_disk_write_failure_returns_none(monkeypatch):
+    row = _row()
+    p, client = _patch_httpx_for_fetch(_make_resp(200, content=b"x", content_type="text/plain"))
+
+    def bad_stage(*args, **kwargs):
+        raise OSError(28, "no space left")
+    monkeypatch.setattr(inbox_uploads, "stage_to_disk", bad_stage)
+
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    client.post.assert_not_called()
+
+
+def test_fetch_and_stage_disk_value_error_returns_none(monkeypatch):
+    row = _row()
+    p, client = _patch_httpx_for_fetch(_make_resp(200, content=b"x", content_type="text/plain"))
+
+    def bad_stage(*args, **kwargs):
+        raise ValueError("oversize after sanity check")
+    monkeypatch.setattr(inbox_uploads, "stage_to_disk", bad_stage)
+
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is None
+    client.post.assert_not_called()
+
+
+def test_fetch_and_stage_httpx_missing_returns_none(monkeypatch):
+    row = _row()
+    # Simulate httpx not installed by making the import fail.
+    import sys
+    real_httpx = sys.modules.pop("httpx", None)
+    monkeypatch.setitem(sys.modules, "httpx", None)
+    try:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    finally:
+        if real_httpx is not None:
+            sys.modules["httpx"] = real_httpx
+        else:
+            sys.modules.pop("httpx", None)
+    assert result is None
+
+
+def test_fetch_and_stage_falls_back_to_extension_mime(monkeypatch):
+    row = _row(name="snap.png", body_extra={"mimeType": ""})  # no mimeType in body
+    # Response also has no content-type so it falls through to mimetypes.guess_type.
+    get_resp = _make_resp(200, content=b"PNG", content_type="")
+    p, _ = _patch_httpx_for_fetch(get_resp)
+    with p:
+        result = inbox_uploads.fetch_and_stage(
+            row, platform_url="http://plat", workspace_id="ws-1", headers={}
+        )
+    assert result is not None
+
+
+# ---------------------------------------------------------------------------
+# rewrite_request_body — URI swap in chat-message bodies
+# ---------------------------------------------------------------------------
+
+
+def test_rewrite_request_body_swaps_pending_uri_in_message_parts():
+    inbox_uploads.get_cache().set("platform-pending:ws/1", "workspace:/local/1")
+    body = {
+        "method": "message/send",
+        "params": {
+            "message": {
+                "parts": [
+                    {"kind": "text", "text": "see this"},
+                    {"kind": "file", "file": {"uri": "platform-pending:ws/1", "name": "a.pdf"}},
+                ]
+            }
+        },
+    }
+    inbox_uploads.rewrite_request_body(body)
+    assert body["params"]["message"]["parts"][1]["file"]["uri"] == "workspace:/local/1"
+
+
+def test_rewrite_request_body_swaps_in_params_parts():
+    inbox_uploads.get_cache().set("platform-pending:ws/2", "workspace:/local/2")
+    body = {
+        "params": {
+            "parts": [
+                {"kind": "file", "file": {"uri": "platform-pending:ws/2"}},
+            ]
+        }
+    }
+    inbox_uploads.rewrite_request_body(body)
+    assert body["params"]["parts"][0]["file"]["uri"] == "workspace:/local/2"
+
+
+def test_rewrite_request_body_swaps_in_top_level_parts():
+    inbox_uploads.get_cache().set("platform-pending:ws/3", "workspace:/local/3")
+    body = {
+        "parts": [{"kind": "file", "file": {"uri": "platform-pending:ws/3"}}]
+    }
+    inbox_uploads.rewrite_request_body(body)
+    assert body["parts"][0]["file"]["uri"] == "workspace:/local/3"
+
+
+def test_rewrite_request_body_leaves_unmatched_uri_unchanged():
+    # No cache entry → URI stays as-is. Agent surfaces the unresolvable
+    # URI rather than the inbox silently dropping the part.
+    body = {
+        "parts": [{"kind": "file", "file": {"uri": "platform-pending:ws/missing"}}]
+    }
+    inbox_uploads.rewrite_request_body(body)
+    assert body["parts"][0]["file"]["uri"] == "platform-pending:ws/missing"
+
+
+def test_rewrite_request_body_leaves_non_pending_uri_unchanged():
+    inbox_uploads.get_cache().set("platform-pending:ws/3", "workspace:/local/3")
+    body = {
+        "parts": [
+            {"kind": "file", "file": {"uri": "workspace:/already-local.pdf"}},
+            {"kind": "file", "file": {"uri": "https://example.com/x.pdf"}},
+        ]
+    }
+    inbox_uploads.rewrite_request_body(body)
+    assert body["parts"][0]["file"]["uri"] == "workspace:/already-local.pdf"
+    assert body["parts"][1]["file"]["uri"] == "https://example.com/x.pdf"
+
+
+def test_rewrite_request_body_skips_non_dict_parts():
+    body = {"parts": ["not a dict", 42, None]}
+    inbox_uploads.rewrite_request_body(body)  # must not raise
+    assert body["parts"] == ["not a dict", 42, None]
+
+
+def test_rewrite_request_body_skips_text_parts():
+    body = {
+        "parts": [{"kind": "text", "text": "platform-pending:ws/should-not-rewrite"}]
+    }
+    inbox_uploads.rewrite_request_body(body)
+    # Text content not touched — only file.uri fields are URIs.
+    assert body["parts"][0]["text"] == "platform-pending:ws/should-not-rewrite"
+
+
+def test_rewrite_request_body_skips_part_without_file_dict():
+    body = {"parts": [{"kind": "file"}]}  # no file key
+    inbox_uploads.rewrite_request_body(body)
+    assert body["parts"] == [{"kind": "file"}]
+
+
+def test_rewrite_request_body_skips_file_without_uri():
+    body = {"parts": [{"kind": "file", "file": {"name": "x.pdf"}}]}
+    inbox_uploads.rewrite_request_body(body)
+    assert body["parts"][0]["file"] == {"name": "x.pdf"}
+
+
+def test_rewrite_request_body_skips_nonstring_uri():
+    body = {"parts": [{"kind": "file", "file": {"uri": None}}]}
+    inbox_uploads.rewrite_request_body(body)  # must not raise
+
+
+def test_rewrite_request_body_handles_non_dict_body():
+    inbox_uploads.rewrite_request_body(None)  # no-op
+    inbox_uploads.rewrite_request_body("string body")  # no-op
+    inbox_uploads.rewrite_request_body([1, 2, 3])  # no-op
+
+
+def test_rewrite_request_body_handles_non_dict_params():
+    body = {"params": "not a dict", "parts": []}
+    inbox_uploads.rewrite_request_body(body)  # must not raise
+
+
+def test_rewrite_request_body_handles_non_dict_message():
+    body = {"params": {"message": "not a dict"}}
+    inbox_uploads.rewrite_request_body(body)  # must not raise
+
+
+def test_rewrite_request_body_handles_non_list_parts():
+    body = {"parts": "not a list"}
+    inbox_uploads.rewrite_request_body(body)  # must not raise
+
+
+def test_rewrite_request_body_handles_non_dict_file():
+    body = {"parts": [{"kind": "file", "file": "not a dict"}]}
+    inbox_uploads.rewrite_request_body(body)  # must not raise