security(upload): cap upload size to prevent memody/disk consumption

add OXICLOUD_CHUNK_MAX_BYTES which correspond to the max upload chunk allowed
    (differs from OXICLOUD_MAX_UPLOAD_SIZE which is the max total size of a file)
    hurl test validate the change

    Streams the request body straight to the chunk file with peak heap of
    ~one HTTP frame, regardless of chunk size or the configured cap. The
    `storage.chunk_max_bytes` config (env `OXICLOUD_CHUNK_MAX_BYTES`,
    default 100 MB) bounds a single PUT — separate from `max_upload_size`
    which governs whole-file uploads. Without this separation, a client
    could submit a chunk up to the whole-file cap (10 GB default) and
    monopolise server memory.

tests/api/chunked_upload_cap.hurl

@@ -0,0 +1,159 @@
+# =============================================================
+# OxiCloud — Chunked upload size cap + streaming verification
+# =============================================================
+# Validates `storage.chunk_max_bytes` (env `OXICLOUD_CHUNK_MAX_BYTES`,
+# set to 4 MiB by `tests/common/server.env`) on the REST chunked upload
+# surface `/api/uploads/{id}`.
+#
+# Two scenarios:
+#   1. SUCCESS path — uploads `hello.txt` (32 bytes) in one chunk and
+#      asserts the stored file's BLAKE3 matches the known hash of the
+#      fixture. Confirms streaming + assembly + dedup integrity.
+#   2. CAP REJECTION — uploads `chunk-over-cap-5mb.bin` (5 MiB) which
+#      exceeds the 4 MiB cap, asserting the server returns 413 Payload
+#      Too Large instead of OOMing or silently truncating.
+#
+# Why REST chunked, not NC chunked: both surfaces share the same
+# `chunk_max_bytes` config; the REST path is JWT-authed (already set
+# up in this Hurl run), the NC path would require minting an app
+# password mid-test.
+# =============================================================
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 1 — Login and capture the JWT token
+# ─────────────────────────────────────────────────────────────
+POST {{base_url}}/api/auth/login
+Content-Type: application/json
+{
+  "username": "{{username}}",
+  "password": "{{password}}"
+}
+
+HTTP 200
+[Captures]
+token: jsonpath "$.access_token"
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 2 — Resolve home folder id (single root folder for admin)
+# ─────────────────────────────────────────────────────────────
+GET {{base_url}}/api/folders
+Authorization: Bearer {{token}}
+
+HTTP 200
+[Captures]
+home_folder_id: jsonpath "$[0].id"
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 3 — Create chunked upload session for hello.txt (32 bytes)
+#           chunk_size = 1 MiB (server minimum is 1 MiB). With
+#           total_size < chunk_size the server computes a single
+#           chunk of `total_size` bytes for index 0.
+# ─────────────────────────────────────────────────────────────
+POST {{base_url}}/api/uploads
+Authorization: Bearer {{token}}
+Content-Type: application/json
+{
+  "filename": "chunked-cap-hello.txt",
+  "folder_id": "{{home_folder_id}}",
+  "content_type": "text/plain",
+  "total_size": 32,
+  "chunk_size": 1048576
+}
+
+HTTP 201
+[Captures]
+upload_id_ok: jsonpath "$.upload_id"
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 4 — Upload the single 32-byte chunk → 200
+# ─────────────────────────────────────────────────────────────
+PATCH {{base_url}}/api/uploads/{{upload_id_ok}}?chunk_index=0
+Authorization: Bearer {{token}}
+Content-Type: application/octet-stream
+file,fixtures/hello.txt;
+
+HTTP 200
+[Asserts]
+header "Upload-Complete" == "true"
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 5 — Complete the upload → 201, capture file id
+# ─────────────────────────────────────────────────────────────
+POST {{base_url}}/api/uploads/{{upload_id_ok}}/complete
+Authorization: Bearer {{token}}
+
+HTTP 201
+[Captures]
+file_id: jsonpath "$.file_id"
+[Asserts]
+jsonpath "$.filename" == "chunked-cap-hello.txt"
+jsonpath "$.size" == 32
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 6 — Verify the stored file's BLAKE3 matches the known
+#           hash of `tests/fixtures/hello.txt`. This proves the
+#           streaming path wrote the exact bytes — no truncation,
+#           no buffering corruption, no off-by-one.
+#
+#           Expected hash:
+#             b2208c5dc33ff951227bd0c139f5eccb04105d6da6a7519ee23f7bc00a17bb5a
+# ─────────────────────────────────────────────────────────────
+GET {{base_url}}/api/files?folder_id={{home_folder_id}}
+Authorization: Bearer {{token}}
+
+HTTP 200
+[Asserts]
+jsonpath "$[?(@.id == '{{file_id}}')].content_hash" includes "b2208c5dc33ff951227bd0c139f5eccb04105d6da6a7519ee23f7bc00a17bb5a"
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 7 — CAP REJECTION: create a session declaring a 5 MiB
+#           chunk and attempt to upload exactly 5 MiB → 413.
+#
+#           The cap fires in `axum::body::to_bytes(req, max_chunk)`
+#           BEFORE the inner chunk-size check, so the server never
+#           materialises the full 5 MiB body in memory.
+# ─────────────────────────────────────────────────────────────
+POST {{base_url}}/api/uploads
+Authorization: Bearer {{token}}
+Content-Type: application/json
+{
+  "filename": "chunked-cap-over.bin",
+  "folder_id": "{{home_folder_id}}",
+  "content_type": "application/octet-stream",
+  "total_size": 5242880,
+  "chunk_size": 5242880
+}
+
+HTTP 201
+[Captures]
+upload_id_big: jsonpath "$.upload_id"
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 8 — Send a 5 MiB chunk → 413 (cap is 4 MiB).
+#           Pre-fix this PATCH would either OOM the server or be
+#           silently treated as an empty body (via the old
+#           `to_bytes(.., usize::MAX).unwrap_or_default()` path).
+# ─────────────────────────────────────────────────────────────
+PATCH {{base_url}}/api/uploads/{{upload_id_big}}?chunk_index=0
+Authorization: Bearer {{token}}
+Content-Type: application/octet-stream
+file,fixtures/chunk-over-cap-5mb.bin;
+
+HTTP 413
+
+
+# ─────────────────────────────────────────────────────────────
+# Step 9 — Clean up the abandoned over-cap session.
+# ─────────────────────────────────────────────────────────────
+DELETE {{base_url}}/api/uploads/{{upload_id_big}}
+Authorization: Bearer {{token}}
+
+HTTP 204