Replace the old upload_pack.go and receive_pack.go test suites in
internal/transport/test/ with the new versions from x/transport/test/.
These new suites test against the new plumbing/transport API.

Replace the old plumbing/transport/ssh package with the new version from
x/transport/ssh. This includes the new auth, handshake, knownhosts, and
sshagent implementations.

Replace the old plumbing/transport/http package with the new version from
x/transport/http. This includes new auth, handshake, dumb HTTP, TLS,
redirect, and proxy implementations.

Replace the old plumbing/transport/git package with the new version from
x/transport/git. Includes new handshake implementation.

Replace the old plumbing/transport/file package with the new version from
x/transport/file. Includes new handshake implementation.

Add plumbing/client from x/client. This package provides scheme-based
transport resolution, replacing the old registry.go functionality.

Replace old transport API usage in remote.go, repository.go, submodule.go,
and options.go with the new plumbing/transport and plumbing/client APIs.

Key changes:
- Replace Auth, InsecureSkipTLS, CABundle, ProxyOptions fields with
  ClientOptions []client.Option on all option structs
- Replace newClient() to use client.New() + transport.ParseURL()
- Collapse Transport.NewSession + Session.Handshake into client.Handshake
- Pass storer to Session.Fetch/Push (new signature)
- Replace transport.NewEndpoint with transport.ParseURL (*url.URL)

Update server and backend packages for the new plumbing/transport API:
- Replace transport.Service type with plain string
- Replace transport.NewEndpoint with transport.ParseURL (*url.URL)
- Replace svc.Name()/service.Name() with transport.ServiceName()
- Update Loader.Load signature from *Endpoint to *url.URL

Update all examples that use authentication or custom HTTP clients
to use the new client.Option pattern instead of the old Auth field
and transport.Register.

Fix all remaining build, test, and lint errors after the transport API
migration so the full stack compiles, passes go vet, and all tests pass.

Highlights:

- Remove NewConn helper; each transport now implements transport.Conn
  directly (sshConn, gitConn, fileConn)
- Surface remote stderr at Push/Fetch via Stderr() io.Reader interface
  instead of at Close() time — the idiomatic Go pattern for subprocess
  error reporting
- Replace UploadPackOptions/ReceivePackOptions with UploadPackRequest/
  ReceivePackRequest in backend packages
- Fix missing closing paren and stale variable references in remote.go
- Update worktree.go to use ClientOptions instead of old fields
- Consolidate duplicate internal/transport/test imports across all
  sub-transport test files
- Refactor duplicated test code into table-driven tests and shared
  setup helpers (file, git, ssh)
- Fix TestHostKeyCallbackHelper_NilFallback to account for
  /etc/ssh/ssh_known_hosts
- Fix gci import ordering across all modified files

Verified: go build, go vet, go test ./..., and example tests all pass.

The go.mod requires v6 but test files still imported v5.

Merge backend/git and backend/http into a single backend package with a
unified API:

- Backend.Serve(ctx, r, w, *Request) — core dispatch for all transports
- Backend.ServeConn(ctx, rwc, *Request) — convenience for full-duplex
  connections (TCP, SSH, pipes)
- Backend.ServeHTTP(w, r) — HTTP adapter (smart + dumb protocols)
- RequestFromProto(*packp.GitProtoRequest) — helper for TCP git daemon

The shared logic (loader resolution, service dispatch, UploadPack/
ReceivePack invocation) lives in Serve. HTTP-specific concerns (routing,
gzip, content-type, dumb file serving) stay in ServeHTTP. Error handling
is the caller's responsibility — Serve returns errors instead of writing
them to the wire.

Delete backend/git/ and backend/http/ subpackages. Update
internal/server/http to import backend directly.

Co-authored-by: Paulo Gomes <[email protected]>
Co-authored-by: Ayman Bagabas <[email protected]>

…sts loading

…rt Connect

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Co-authored-by: Copilot Autofix powered by AI <[email protected]>

plumbing: transport, replace transport API with new design