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fix(web): only use a public address on a fixed listener port (#1862)

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Addresses Copilot review round 2. A reverse proxy routes a public address to
one stable port, so neither MCP_SANDBOX_FULL_ADDRESS nor
MCP_APP_ORIGIN_FULL_ADDRESS is used when the listener's port is OS-assigned:
an explicit 0, a config-time collision resolved to 0, or the EADDRINUSE
fallback. Validation warnings also stop echoing the URL path.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HzuzRPJv7M8wGe3wyw5sSg
Signed-off-by: cliffhall <cliff@futurescale.com>
This commit is contained in:
cliffhall 2026-09-14 01:10:29 -04:00
commit 925461a043
1 changed files with 110 additions and 22 deletions
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2
docs/environment-variables.md
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@ -41,7 +41,7 @@ The sandbox and app-origin servers advertise a URL built from their own bind (`h
| `MCP_SANDBOX_FULL_ADDRESS` | web | `http://<bind host>:<sandbox port>/sandbox` | Public URL of the MCP Apps sandbox proxy, returned as `sandboxUrl` by `GET /api/config` and printed in the banner (e.g. `https://inspector-sandbox.example.com/sandbox`). A bare origin gets `/sandbox` appended. An empty value counts as unset. |
| `MCP_APP_ORIGIN_FULL_ADDRESS` | web | `http://<bind host>:<app-origin port>` | Public origin that `_meta.ui.domain` app documents are published under (e.g. `https://inspector-apps.example.com`). **Origin only** — a path is refused, since documents are served at `<origin>/app-document/<id>`. An empty value counts as unset. |
Both are **refused** — ignored with a warning, keeping the bind-derived address — when the value is not an absolute `http(s)` URL, carries credentials, a query string, a fragment or a wildcard, or is a bracketed IPv6 literal. ⚠️ **Each needs its own origin.** The MCP Apps spec requires the sandbox origin to differ from the Inspector's, so a sandbox address sharing an `ALLOWED_ORIGINS` origin is refused (`https://inspector.example.com/sandbox` behind the same hostname as the UI is the common case), as is an app origin equal to the Inspector's or the sandbox's. Neither is used if its pinned port was taken at startup and the server fell back to an OS-assigned one, since the proxy would route it to the wrong listener. A plain-`http` address while `ALLOWED_ORIGINS` lists an `https` origin is used, but warned about: the browser blocks it as mixed content.
Both are **refused** — ignored with a warning, keeping the bind-derived address — when the value is not an absolute `http(s)` URL, carries credentials, a query string, a fragment or a wildcard, or is a bracketed IPv6 literal. ⚠️ **Each needs its own origin.** The MCP Apps spec requires the sandbox origin to differ from the Inspector's, so a sandbox address sharing an `ALLOWED_ORIGINS` origin is refused (`https://inspector.example.com/sandbox` behind the same hostname as the UI is the common case), as is an app origin equal to the Inspector's or the sandbox's. Neither is used unless its listener is on a fixed port — not when the port is `0`, and not when the pinned port was taken at startup (or collided with another Inspector port) and the server fell back to an OS-assigned one — since the proxy has no stable port to route it to. A plain-`http` address while `ALLOWED_ORIGINS` lists an `https` origin is used, but warned about: the browser blocks it as mixed content.
## Behavior