feat(cua-driver): add private loopback envelope HTTP carrier

libs/cua-driver/docs/private-envelope-http.md

@@ -0,0 +1,73 @@
+# Private typed envelope HTTP carrier
+
+This carrier connects unary HTTP requests to `DriverEnvelopeReceiver`. It is
+disabled unless the trusted launcher sets `CUA_DRIVER_ENVELOPE_HTTP_PORT` to a
+nonzero port. It binds only to `127.0.0.1` and fails startup if binding fails.
+No non-loopback binding option is provided.
+
+This is an implementation contract, not a released Fleet setup guide. A later
+image/service change must connect the loopback endpoint to Fleet's existing
+authorized private named-service route. Do not expose this endpoint directly:
+it does not authenticate callers. IDs and generations are lifecycle markers,
+not credentials. The carrier introduces no bearer token or pairing scheme.
+
+## Wire contract
+
+All requests use HTTP/1.1. POST bodies require one valid `Content-Length`.
+Responses are JSON with `Connection: close`; pipelined requests are not executed.
+Browser-origin requests, transfer encoding, duplicate lengths, and query strings
+are refused. There is no CORS support.
+
+| Request                              | Body                              | Result                                                              |
+| ------------------------------------ | --------------------------------- | ------------------------------------------------------------------- |
+| `POST /v1/connections`               | `{}`                              | `connection_id`, `generation`, `public_session`, and `capabilities` |
+| `POST /v1/connections/{id}/exchange` | Canonical `DriverRequestEnvelope` | Canonical `DriverResponseEnvelope`                                  |
+| `POST /v1/connections/{id}/cancel`   | `{"request_id":"REQUEST_ID"}`     | `{"ok":true}`                                                       |
+| `DELETE /v1/connections/{id}`        | Empty or `{}`                     | `{"ok":true}`                                                       |
+
+Every connection-specific request requires `X-Cua-Driver-Generation` with the
+value returned at creation. Missing generations fail with HTTP 400, absent
+connections with 404, and mismatches with 409. A client must not reopen a
+connection automatically after those failures.
+
+Creation binds a Standard session with a one-hour maximum lifetime and a
+five-minute idle lifetime. The immutable runtime ceiling still applies:
+incompatible runtimes refuse creation. This slice does not inherit unrestricted
+mode or accept permission modes, manifests, or arbitrary session options from
+the wire. Ordinary typed calls use `session=None`; operations requiring a
+session label use the returned `public_session`.
+
+`capabilities` contains `minimum_envelope_version`, `maximum_envelope_version`,
+and `supports_cancellation`. This carrier supports envelope version 1 and
+cancellation. Independent `bind_session` requests are not implemented; the
+returned canonical Driver root already owns one bound session.
+
+## Resource and cleanup limits
+
+- Request headers: 16 KiB; request body: 1 MiB.
+- Response body: 16 MiB. An oversized exchange closes its session and returns
+  `response_too_large` with unknown completion; it must not be replayed.
+- Live connection entries: 64, reaped after five idle minutes.
+- HTTP tasks: 64; exchanges: 32, admitted without an unbounded wait queue.
+  Remaining task capacity permits cancellation and close during action load.
+- Request reading and response writing: ten-second limits. Exchange deadlines
+  and per-connection replay prevention are enforced by the receiver.
+
+Close is idempotent and retains the closed request ledger until idle removal.
+Idle reaping skips active exchanges. Shutdown cancels the listener and its
+connection tasks and closes owned sessions. It does not shut down the shared
+Driver runtime or computer-server, release a Fleet claim, or delete a pool.
+
+## Verification boundary
+
+Synthetic parser/routing tests cover malformed input, limits, generation
+checks, raw results, close, active-session reaping, cancellation under full
+exchange load, and oversized responses. Run them from `libs/cua-driver/rust`:
+
+```sh
+cargo test -p cua-driver --bin cua-driver driver_service_http --locked
+```
+
+These tests do not establish guest network isolation, Fleet authorization,
+image packaging, real desktop effects, or compatibility with a released Python
+client. Those remain explicit integration and qualification gates.

libs/cua-driver/rust/crates/cua-driver/Cargo.toml

@@ -21,6 +21,7 @@ cua-driver-sdk = { path = "../cua-driver-sdk" }
 cursor-overlay = { path = "../cursor-overlay" }
 pip-preview = { path = "../pip-preview" }
 async-trait = "0.1"
+httparse = "1.10.1"
 base64 = { workspace = true }
 uuid = { workspace = true }
 zeroize = { workspace = true }