gateway: honour LITELLM_CORS_ORIGINS from app env; expose cost headers (#38, #39)

start.sh hardcoded and exported LITELLM_CORS_ORIGINS, so the Cloudron app env that is meant to control it was silently overridden — the change I made earlier tonight looked applied and was inert. It now defaults only when unset, so the app env wins, and the co-op decision to allow all origins (co-op/support#38) actually takes effect. Comment rewritten for the current version and the reasoning. Also adds patch_expose_cost_headers.py (wired into the Dockerfile) so x-litellm-response-cost* can be read by cross-origin clients (co-op/support#39); upstream closed the request as stale, so it is handled at the app layer like the other patches.

patch_expose_cost_headers.py

@@ -0,0 +1,80 @@
+"""Expose LiteLLM's per-request cost headers to cross-origin browser clients.
+
+MEMBER REQUEST (co-op/support#39, 2026-10-31). Browser JS calling the gateway from
+another origin cannot read a response header unless the server names it in
+Access-Control-Expose-Headers. LiteLLM sets
+
+    expose_headers=LITELLM_UI_ALLOW_HEADERS
+
+which covers seven names (semantic-filter, guardrail, cache-key, ...) and none of
+the cost ones — so `x-litellm-response-cost*` reads as null in JS even though the
+proxy sends those headers on the response. Upstream closed the request
+(BerriAI/litellm#33123) as stale, so it has to be handled here at the app layer,
+exactly like the other patches in this directory.
+
+Additive only. It lets a caller read per-request pricing for requests they made
+with their own API key — numbers already present in the response body for
+non-streaming calls, and already visible in their dashboard. It exposes no prompt,
+key, or account data, and no other member's usage.
+
+Run at BUILD time (the runtime rootfs is read-only under Cloudron). Non-fatal, per
+house rule: if upstream moves or rewrites this call, WARN and exit 0 — a missing
+convenience header must never keep the gateway from booting.
+
+Regression check: after a deploy, a browser request from an unrelated origin should
+see the cost headers listed in Access-Control-Expose-Headers on the response.
+"""
+from pathlib import Path
+import sys
+
+# The header names the proxy can set, taken from the running image rather than
+# guessed: grep -rhoE 'x-litellm-[a-z0-9-]*cost[a-z0-9-]*' over the litellm package.
+COST_HEADERS = [
+    "x-litellm-response-cost",
+    "x-litellm-response-cost-input",
+    "x-litellm-response-cost-output",
+    "x-litellm-response-cost-original",
+    "x-litellm-response-cost-discount-amount",
+    "x-litellm-response-cost-margin-amount",
+    "x-litellm-response-cost-margin-percent",
+    "x-litellm-response-cost-cache-creation",
+    "x-litellm-response-cost-cache-read",
+    "x-litellm-response-cost-reasoning",
+    "x-litellm-response-cost-tool-usage",
+    "x-litellm-classifier-cost",
+]
+
+OLD = "    expose_headers=LITELLM_UI_ALLOW_HEADERS,\n"
+NEW = (
+    "    expose_headers=LITELLM_UI_ALLOW_HEADERS\n"
+    "    + [\n"
+    + "".join(f'        "{h}",\n' for h in COST_HEADERS)
+    + "    ],\n"
+)
+
+
+def main() -> int:
+    # Glob rather than pin a Python version: the venv path moves when the base
+    # image bumps its interpreter, and a stale path would silently skip the patch.
+    candidates = sorted(Path("/app/.venv/lib").glob("python3*/site-packages/litellm/proxy/proxy_server.py"))
+    if not candidates:
+        print("WARN expose-cost-headers: proxy_server.py not found under /app/.venv/lib — skipping")
+        return 0
+
+    target = candidates[-1]
+    src = target.read_text()
+    if "x-litellm-response-cost-input" in src:
+        print("expose-cost-headers: already applied")
+        return 0
+    found = src.count(OLD)
+    if found != 1:
+        print(f"WARN expose-cost-headers: expected exactly 1 CORS middleware call, found {found} — skipping")
+        return 0
+
+    target.write_text(src.replace(OLD, NEW))
+    print(f"expose-cost-headers: appended {len(COST_HEADERS)} cost header names to expose_headers in {target}")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())