fix(remote): auth /acp dial via Authorization header, offer only acp.v1

[brettchien]

Symptom

Activating the remote connection dials wss://…/acp, saves config, then fails:

ERROR remote: dial wss://orca-acp.brettchien.cc/acp:
  WebSocket protocol error: SubProtocol error: Server sent an invalid subprotocol

TLS, the Cloudflare upgrade, and auth are all fine — it dies purely in sub-protocol negotiation.

Root cause (client-side, tokio-tungstenite 0.23)

bearer_subprotocol() returns openab.bearer.<token>, acp.v1, and remote.rs set that as a single Sec-WebSocket-Protocol header. tokio-tungstenite 0.23 parses the request's offer with split(",") without trimming:

// tungstenite handshake/client.rs:189
subprotocols.to_str()?.split(",").map(|s| s.to_string()).collect()
// -> ["openab.bearer.<token>", " acp.v1"]   // note the leading space

so when the server echoes acp.v1, the response check fails:

// client.rs:270-274
if !accepted_subprotocols.contains(&returned_subprotocol) { InvalidSubProtocol }
// " acp.v1" != "acp.v1"  ->  error

Browser / Python clients keep their own offer list and trim, so they were unaffected — which is why the gateway tested healthy.

Note: appending two separate Sec-WebSocket-Protocol header values does not work either — tungstenite's extract_subprotocols_from_request reads only the first via headers().get().

Fix

Studio is a native (non-browser) client, so:

• send the bearer in the Authorization: Bearer <token> header (the gateway reads ws_bearer_token from it), and
• offer only acp.v1 as the sub-protocol — one clean token that matches the server's echo.

Bonus: the secret bearer no longer rides Sec-WebSocket-Protocol, which proxies (Cloudflare is in the path) are prone to log. bearer_subprotocol() stays as the documented browser-only form, guarded by a new regression test.

Verification

• Live, end-to-end: a compliant client using Authorization header + subprotocols=[acp.v1] connects and negotiates acp.v1 against wss://orca-acp.brettchien.cc/acp; a wrong bearer gets HTTP 401. (Server side verified by Jellyfish against openab-gateway acp_server.rs.)
• cargo test -p acp-tunnel — 19 passed (incl. new acp_subprotocol_is_a_single_clean_token).
• studio-desktop compilation left to CI (desktop.yml) — separate GUI workspace, not built on the ECS host to avoid OOM.

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