agent/new: sub-agent support via rdwr with prompt=

Writing to session/{s}/agent/new with a prompt= key now blocks
until the agent completes its task, then returns the reply and
destroys the transient agent. Without prompt=, behaves as before
(creates agent, returns ID).

Also:
- Move ParsePayload/UnescapeValue to shared ollie/toolsrv package
- Remove duplicate implementations from cmd/toolsrv/internal/server
- Add session.CreateAgentWithParams for direct AgentParams usage
- Eliminate flattenParams/unescapeValue redundancy in fs package

cmd/olliesrv/internal/fs/spec.go

@@ -288,13 +288,32 @@ func buildSessionChildren(
 		),
 		virtfs.DirNode("agent",
 			virtfs.FileNode("new", 0666,
-				virtfs.Rdwr(func(_ context.Context, data []byte) ([]byte, error) {
-					ag, err := session.CreateAgent(s.Name(), strings.Fields(string(data)))
+				virtfs.Doc("Create agent. With prompt=, runs as sub-agent: blocks until done, returns reply."),
+				virtfs.Rdwr(func(ctx context.Context, data []byte) ([]byte, error) {
+					params, prompt := parseAgentNewRequest(data)
+
+					ag, err := session.CreateAgentWithParams(s.Name(), params)
 					if err != nil {
 						return nil, fmt.Errorf("create agent: %w", err)
 					}
 					wireAgentEvents(s.ID, ag)
-					return []byte(ag.ID() + "\n"), nil
+
+					if prompt == "" {
+						return []byte(ag.ID() + "\n"), nil
+					}
+
+					// Sub-agent mode: submit, block until idle, return reply, destroy.
+					session.PublishEvent("session."+s.ID+".agent."+ag.ID()+".new", "")
+					ag.Submit(ctx, prompt)
+					ag.EnsureTrailingNewline()
+					reply := ag.Reply()
+					s.RemoveAgent(ag.ID())
+					session.PublishEvent("session."+s.ID+".agent."+ag.ID()+".kill", "")
+
+					if reply == "" {
+						return []byte("(no reply)\n"), nil
+					}
+					return []byte(reply), nil
 				}),
 			),
 			virtfs.FileNode("idx", 0444,

cmd/olliesrv/internal/fs/support.go

@@ -10,6 +10,7 @@ import (
 
 	"ollie/cmd/olliesrv/internal/agent"
 	"ollie/cmd/olliesrv/internal/session"
+	"ollie/toolsrv"
 	"ollie/virtfs"
 )
 
@@ -77,3 +78,54 @@ var (
 		return helpText
 	}
 )
+
+// parseAgentNewRequest parses agent/new payloads in both formats:
+//   - Newline-separated key=value (new format, supports multi-line values via \n escape)
+//   - Space-separated key=value (legacy format from GUI)
+//
+// A bare word (no =) is treated as the profile name (legacy positional arg).
+// Returns AgentParams and the prompt (empty if not a sub-agent request).
+func parseAgentNewRequest(data []byte) (session.AgentParams, string) {
+	s := strings.TrimSpace(string(data))
+	if s == "" {
+		return session.AgentParams{Profile: "default"}, ""
+	}
+
+	var tokens []string
+	if strings.Contains(s, "\n") {
+		tokens = strings.Split(s, "\n")
+	} else {
+		tokens = strings.Fields(s)
+	}
+
+	p := session.AgentParams{Profile: "default"}
+	var prompt string
+	for _, tok := range tokens {
+		tok = strings.TrimSpace(tok)
+		if tok == "" {
+			continue
+		}
+		if k, v, ok := strings.Cut(tok, "="); ok {
+			v = toolsrv.UnescapeValue(v)
+			switch k {
+			case "cwd":
+				p.CWD = v
+			case "backend":
+				p.Backend = v
+			case "model":
+				p.Model = v
+			case "name":
+				p.Name = v
+			case "remote":
+				p.Remote = v
+			case "profile":
+				p.Profile = v
+			case "prompt":
+				prompt = v
+			}
+		} else if p.Profile == "default" {
+			p.Profile = tok
+		}
+	}
+	return p, prompt
+}

cmd/olliesrv/internal/session/registry.go

@@ -457,12 +457,7 @@ func buildAgent(sess *Session, p AgentParams) (*agent.Agent, error) {
 // CreateAgent creates a new agent within an existing session.
 // Args: [profile] [key=value...] where keys include name, backend, model, remote, cwd.
 func CreateAgent(sessName string, args []string) (*agent.Agent, error) {
-	sess := Lookup(sessName)
-	if sess == nil {
-		return nil, fmt.Errorf("session not found: %s", sessName)
-	}
-
-	// Parse args
+	// Parse args into AgentParams.
 	p := AgentParams{Profile: "default"}
 	for _, arg := range args {
 		if k, v, ok := strings.Cut(arg, "="); ok {
@@ -482,6 +477,20 @@ func CreateAgent(sessName string, args []string) (*agent.Agent, error) {
 			p.Profile = arg
 		}
 	}
+	return CreateAgentWithParams(sessName, p)
+}
+
+// CreateAgentWithParams creates a new agent within an existing session using
+// a pre-built AgentParams struct.
+func CreateAgentWithParams(sessName string, p AgentParams) (*agent.Agent, error) {
+	sess := Lookup(sessName)
+	if sess == nil {
+		return nil, fmt.Errorf("session not found: %s", sessName)
+	}
+
+	if p.Profile == "" {
+		p.Profile = "default"
+	}
 
 	if p.CWD == "" {
 		return nil, fmt.Errorf("cwd= is required when creating an agent")

cmd/toolsrv/internal/server/proc.go

@@ -217,7 +217,7 @@ func (st *State) allocID() int {
 // If background is true, returns immediately with pid.
 func (st *State) NewProc(ctx context.Context, payload string, background bool) (result string, pid int, err error) {
 	// Parse payload
-	args := ParsePayload(payload)
+	args := toolsrv.ParsePayload(payload)
 	toolName := args["tool"]
 	if toolName == "" {
 		return "", 0, fmt.Errorf("missing 'tool' in payload")

cmd/toolsrv/internal/server/proc_test.go

@@ -5,6 +5,8 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"ollie/toolsrv"
 )
 
 func TestState_Basic(t *testing.T) {
@@ -189,10 +191,10 @@ func TestParsePayload(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		got := ParsePayload(tt.input)
+		got := toolsrv.ParsePayload(tt.input)
 		for k, v := range tt.want {
 			if got[k] != v {
-				t.Errorf("ParsePayload(%q)[%q] = %q, want %q", tt.input, k, got[k], v)
+				t.Errorf("toolsrv.ParsePayload(%q)[%q] = %q, want %q", tt.input, k, got[k], v)
 			}
 		}
 	}

toolsrv/parse.go

@@ -1,9 +1,9 @@
-// parse.go - Key=value payload parsing for toolsrv.
-package server
+// parse.go — Shared key=value payload parsing.
+package toolsrv
 
 import "strings"
 
-// ParsePayload parses key=value lines into a map.
+// ParsePayload parses newline-separated key=value pairs into a map.
 // Values are unescaped: \n → newline, \\ → backslash.
 func ParsePayload(payload string) map[string]string {
 	args := make(map[string]string)
@@ -24,8 +24,11 @@ func ParsePayload(payload string) map[string]string {
 	return args
 }
 
-// UnescapeValue reverses escape sequences: \n → newline, \\ → backslash.
+// UnescapeValue reverses wire-format escape sequences: \n → newline, \\ → backslash.
 func UnescapeValue(s string) string {
+	if !strings.ContainsRune(s, '\\') {
+		return s
+	}
 	result := make([]byte, 0, len(s))
 	for i := 0; i < len(s); i++ {
 		if s[i] == '\\' && i+1 < len(s) {