remote: fetch host_info, inject PWD for remote prompt resolution

prompt_resolver: when cmd.Dir cannot be set (remote CWD does not exist
locally), inject PWD=cwd into subprocess env so envsubst in prime sees
the correct working directory.

remote.Server: fetch host_info RPC after connect, expose HostInfo struct
with platform, arch, is_git_repo for the session to pass to prompts.

pkg/agent/prompt_resolver.go

@@ -46,11 +46,13 @@ func resolveExecPrompt(cmds []string, cwd string, env []string) (string, error)
 		if cwd != "" {
 			if info, err := os.Stat(cwd); err == nil && info.IsDir() {
 				cmd.Dir = cwd
+			} else {
+				// CWD doesn't exist locally (remote session). Inject PWD so
+				// scripts that use ${PWD} via envsubst see the correct value.
+				env = append(env, "PWD="+cwd)
 			}
 		}
-		if len(env) > 0 {
-			cmd.Env = append(os.Environ(), env...)
-		}
+		cmd.Env = append(os.Environ(), env...)
 		var stdout, stderr bytes.Buffer
 		cmd.Stdout = &stdout
 		cmd.Stderr = &stderr
@@ -101,11 +103,17 @@ func resolveStringPrompt(prompt, cwd string, env []string) (string, error) {
 		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 		defer cancel()
 		cmd := exec.CommandContext(ctx, "sh", "-c", cmdStr)
+		var cmdEnv []string
 		if cwd != "" {
 			if info, err := os.Stat(cwd); err == nil && info.IsDir() {
 				cmd.Dir = cwd
+			} else {
+				cmdEnv = append(cmdEnv, "PWD="+cwd)
 			}
 		}
+		if len(cmdEnv) > 0 {
+			cmd.Env = append(os.Environ(), cmdEnv...)
+		}
 		var stdout, stderr bytes.Buffer
 		cmd.Stdout = &stdout
 		cmd.Stderr = &stderr

pkg/remote/remote.go

@@ -31,6 +31,13 @@ import (
 //go:embed bootstrap.sh
 var bootstrapTemplate string
 
+// HostInfo holds environment details from the remote host.
+type HostInfo struct {
+	Platform   string `json:"platform"`
+	Arch       string `json:"arch"`
+	IsGitRepo  bool   `json:"is_git_repo"`
+}
+
 // Server implements tools.Server by forwarding calls to a remote
 // ollie-remote process over SSH.
 type Server struct {
@@ -41,6 +48,7 @@ type Server struct {
 	enc    *json.Encoder
 	dec    *json.Decoder
 	nextID atomic.Int64
+	Info   HostInfo
 }
 
 // Config holds the parameters for connecting to a remote host.
@@ -179,6 +187,15 @@ func Dial(ctx context.Context, cfg Config) (*Server, error) {
 		return nil, fmt.Errorf("remote ping failed: %w", err)
 	}
 
+	// Fetch remote host info for prompt resolution.
+	// FIXME: This duplicates information that prime scripts also try to detect
+	// locally (platform, is_git_repo). Eventually unify so prompt resolution
+	// always uses these env vars rather than running local checks against a
+	// non-existent remote CWD.
+	if info, err := s.fetchHostInfo(ctx); err == nil {
+		s.Info = info
+	}
+
 	return s, nil
 }
 
@@ -300,6 +317,35 @@ func (s *Server) CallTool(ctx context.Context, tool string, args json.RawMessage
 	return resp.Result, nil
 }
 
+// fetchHostInfo retrieves environment details from the remote host.
+func (s *Server) fetchHostInfo(ctx context.Context) (HostInfo, error) {
+	id := s.nextID.Add(1)
+	req := rpcRequest{
+		JSONRPC: "2.0",
+		ID:      id,
+		Method:  "host_info",
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if err := s.enc.Encode(req); err != nil {
+		return HostInfo{}, err
+	}
+	var resp rpcResponse
+	if err := s.dec.Decode(&resp); err != nil {
+		return HostInfo{}, err
+	}
+	if resp.Error != nil {
+		return HostInfo{}, fmt.Errorf("%s", resp.Error.Message)
+	}
+	var info HostInfo
+	if err := json.Unmarshal(resp.Result, &info); err != nil {
+		return HostInfo{}, err
+	}
+	return info, nil
+}
+
 // ping verifies the remote server is responsive.
 func (s *Server) ping(ctx context.Context) error {
 	id := s.nextID.Add(1)