[roychying]

Why?

SubmitQueue reads Phabricator through Conduit from more than one place, and each caller encodes requests, authenticates and parses Conduit's result envelope its own way. A shared client gives them one encoding, one auth placement and one error shape, and gives the planned Phabricator support in the Runway merger a client from day one.

What?

• New platform/conduit: NewClient(httpClient, token) and Call(ctx, method, params, result).
  • Sends params as JSON with the token in __conduit__. Conduit ignores api.token once the parameters are JSON, so the token lives on the client rather than in a transport.
  • A non-200 reply is a platform/http.StatusError. A Conduit error_code is a typed *conduit.Error; Conduit returns those with HTTP 200, a rejected token (ERR-INVALID-SESSION) included.
  • A null result or an empty array (PHP's empty map) leaves the caller's result untouched.
  • No per-method wrappers: typed requests and results stay with each caller.
• The encoding and auth placement were checked against a production Phabricator for differential.querydiffs, differential.revision.search and differential.getcommitmessage.

Test Plan

bazel test //platform/conduit/...

Issue