fs: unify ctl — all levels use rdwrHandler + rdwrDispatch

Root, session, and agent ctl files all share the same dispatch
mechanism: rdwrHandler map → rdwrDispatch → Request (rdwr).

- ctlHandler/ctlDispatch (write-only) removed
- Root and session ctl upgraded to Request (rdwr), return 'ok'
- systemprompt moved to agent ctl command
- nopRead removed (dead)

data/scripts/o

@@ -33,7 +33,7 @@ ROOT_ENTRIES="session bypass agents backends models help ctl eventwait complete
 SESSION_FILES="env paused connected ctl name id bypass"
 
 # Agent-level files (exist under session/{name}/agent/{name}/)
-AGENT_FILES="prompt fifo chat chat.raw statewait log plan cfg ctl stats systemprompt name id proc"
+AGENT_FILES="prompt fifo chat chat.raw statewait log plan cfg ctl stats name id proc"
 
 is_root_path() {
     local path="$1"

fs/ctl.go

@@ -5,24 +5,23 @@ import (
 	"strings"
 )
 
-// ctlHandler is a function that handles a single ctl command.
-type ctlHandler func(args []string, ctx HandlerCtx) error
+// rdwrHandler is a request-response ctl command handler.
+type rdwrHandler func(ctx HandlerCtx, args []string) ([]byte, error)
 
-// ctlDispatch returns a Write handler that dispatches based on the first
-// whitespace-delimited word in the input. The map keys are command names;
-// values are the handlers. If the command is unknown, an error is returned.
-func ctlDispatch(handlers map[string]ctlHandler) func(HandlerCtx, []byte) error {
-	return func(ctx HandlerCtx, data []byte) error {
+// rdwrDispatch returns a Request handler that dispatches based on the first
+// whitespace-delimited word in the input.
+func rdwrDispatch(handlers map[string]rdwrHandler) func(HandlerCtx, []byte) ([]byte, error) {
+	return func(ctx HandlerCtx, data []byte) ([]byte, error) {
 		input := strings.TrimSpace(string(data))
 		if input == "" {
-			return nil
+			return nil, nil
 		}
 		parts := strings.Fields(input)
 		cmd := parts[0]
 		h, ok := handlers[cmd]
 		if !ok {
-			return fmt.Errorf("unknown ctl command: %s", cmd)
+			return nil, fmt.Errorf("unknown ctl command: %s", cmd)
 		}
-		return h(parts[1:], ctx)
+		return h(ctx, parts[1:])
 	}
 }

fs/handlers.go

@@ -97,25 +97,25 @@ func readTools(_ HandlerCtx) ([]byte, error) {
 	return []byte(sb.String()), nil
 }
 
-func writeRootCtl(ctx HandlerCtx, data []byte) error {
-	handlers := map[string]ctlHandler{
-		"invalidate": func(_ []string, _ HandlerCtx) error {
+func requestRootCtl(ctx HandlerCtx, data []byte) ([]byte, error) {
+	handlers := map[string]rdwrHandler{
+		"invalidate": func(ctx HandlerCtx, _ []string) ([]byte, error) {
 			if ctx.Models != nil {
 				ctx.Models.Invalidate()
 			}
 			if ctx.Invalidate != nil {
 				ctx.Invalidate()
 			}
-			return nil
+			return []byte("ok\n"), nil
 		},
-		"kill": func(_ []string, _ HandlerCtx) error {
+		"kill": func(ctx HandlerCtx, _ []string) ([]byte, error) {
 			if ctx.Shutdown != nil {
 				ctx.Shutdown()
 			}
-			return nil
+			return []byte("ok\n"), nil
 		},
 	}
-	return ctlDispatch(handlers)(ctx, data)
+	return rdwrDispatch(handlers)(ctx, data)
 }
 
 func readEventwait(_ HandlerCtx) ([]byte, error) {
@@ -320,38 +320,40 @@ func readSessionConnected(ctx HandlerCtx) ([]byte, error) {
 	return []byte("false\n"), nil
 }
 
-func writeSessionCtl(ctx HandlerCtx, data []byte) error {
-	handlers := map[string]ctlHandler{
-		"kill": func(_ []string, _ HandlerCtx) error {
+func requestSessionCtl(ctx HandlerCtx, data []byte) ([]byte, error) {
+	handlers := map[string]rdwrHandler{
+		"kill": func(ctx HandlerCtx, _ []string) ([]byte, error) {
 			ctx.Remove()
-			return nil
+			return []byte("ok\n"), nil
 		},
-		".": func(_ []string, _ HandlerCtx) error {
+		".": func(ctx HandlerCtx, _ []string) ([]byte, error) {
 			ctx.Remove()
-			return nil
+			return []byte("ok\n"), nil
 		},
-		"save": func(_ []string, _ HandlerCtx) error {
+		"save": func(ctx HandlerCtx, _ []string) ([]byte, error) {
 			if ctx.Session.Core != nil {
 				ctx.Session.Core.Save()
 			}
-			return nil
+			return []byte("ok\n"), nil
 		},
-		"invalidate": func(_ []string, _ HandlerCtx) error {
+		"invalidate": func(ctx HandlerCtx, _ []string) ([]byte, error) {
 			ctx.Session.InvalidateModelsCache()
-			return nil
+			return []byte("ok\n"), nil
 		},
-		"pause": func(_ []string, _ HandlerCtx) error {
-			return ctx.Session.Pause()
+		"pause": func(ctx HandlerCtx, _ []string) ([]byte, error) {
+			if err := ctx.Session.Pause(); err != nil {
+				return nil, err
+			}
+			return []byte("ok\n"), nil
 		},
-		"resume": func(_ []string, _ HandlerCtx) error {
-			return ctx.Session.Resume()
+		"resume": func(ctx HandlerCtx, _ []string) ([]byte, error) {
+			if err := ctx.Session.Resume(); err != nil {
+				return nil, err
+			}
+			return []byte("ok\n"), nil
 		},
 	}
-	err := ctlDispatch(handlers)(ctx, data)
-	if err != nil {
-		return fmt.Errorf("session ctl: %w", err)
-	}
-	return nil
+	return rdwrDispatch(handlers)(ctx, data)
 }
 
 func readSessionName(ctx HandlerCtx) ([]byte, error) {
@@ -656,24 +658,9 @@ func writeAgentCfg(ctx HandlerCtx, data []byte) error {
 }
 
 func requestAgentCtl(ctx HandlerCtx, data []byte) ([]byte, error) {
-	input := strings.TrimSpace(string(data))
-	if input == "" {
-		return nil, nil
-	}
-	parts := strings.Fields(input)
-	cmd := parts[0]
-	args := parts[1:]
-
-	h, ok := agentCtlHandlers[cmd]
-	if !ok {
-		return nil, fmt.Errorf("unknown ctl command: %s", cmd)
-	}
-	return h(ctx, args)
+	return rdwrDispatch(agentCtlHandlers)(ctx, data)
 }
 
-// rdwrHandler is a request-response ctl command handler.
-type rdwrHandler func(ctx HandlerCtx, args []string) ([]byte, error)
-
 var agentCtlHandlers = map[string]rdwrHandler{
 	"kill": func(ctx HandlerCtx, _ []string) ([]byte, error) {
 		if ctx.Session.Core != nil {
@@ -784,6 +771,9 @@ var agentCtlHandlers = map[string]rdwrHandler{
 		ctx.Agent.SetCWD(dir)
 		return []byte(dir + "\n"), nil
 	},
+	"systemprompt": func(ctx HandlerCtx, _ []string) ([]byte, error) {
+		return []byte(ctx.Agent.SystemPrompt() + "\n"), nil
+	},
 }
 
 func readAgentStats(ctx HandlerCtx) ([]byte, error) {
@@ -793,10 +783,6 @@ func readAgentStats(ctx HandlerCtx) ([]byte, error) {
 	return []byte(s), nil
 }
 
-func readAgentSystemprompt(ctx HandlerCtx) ([]byte, error) {
-	return []byte(ctx.Agent.SystemPrompt() + "\n"), nil
-}
-
 func readAgentName(ctx HandlerCtx) ([]byte, error) {
 	return []byte(ctx.Agent.Name() + "\n"), nil
 }
@@ -883,6 +869,3 @@ func removeProcess(ctx HandlerCtx) error {
 	return nil
 }
 
-func nopRead(_ HandlerCtx) ([]byte, error) {
-	return nil, nil
-}

fs/spec.go

@@ -108,7 +108,7 @@ var treeSpec = DirNode("/",
 
 	FileNode("ctl", 0666,
 		Doc("Server control. Write: 'invalidate' (refresh caches), 'kill' (shutdown server)"),
-		Write(writeRootCtl),
+		Request(requestRootCtl),
 	),
 
 	FileNode("eventwait", 0444,
@@ -176,9 +176,8 @@ FileNode("generate", 0666,
 			),
 
 			FileNode("ctl", 0666,
-				Doc("Session control. Write: 'kill' (destroy), 'save', 'invalidate', 'pause', 'resume'."),
-				Read(nopRead),
-				Write(writeSessionCtl),
+				Doc("Session control: kill, save, invalidate, pause, resume."),
+				Request(requestSessionCtl),
 			),
 
 			FileNode("name", 0666,
@@ -274,11 +273,6 @@ FileNode("generate", 0666,
 						Read(readAgentStats),
 					),
 
-					FileNode("systemprompt", 0444,
-						Doc("Fully rendered system prompt for this agent."),
-						Read(readAgentSystemprompt),
-					),
-
 					FileNode("name", 0666,
 						Doc("Agent display name. Read: current name. Write: rename agent."),
 						Read(readAgentName),

prompts/system_prompt.md

@@ -181,10 +181,8 @@ Each agent has its own directory. The `{aname}` is the agent's numeric ID (stabl
 | `chat.raw`    | read  | Conversation (full markup with block markers) |
 | `statewait`   | read  | Blocks until state changes; returns new value |
 | `cfg`         | r/w   | Agent config: backend, model, cwd, params (key=value) |
-| `ctl`         | rdwr  | Control: stop, compact, clear, inject, agent, model, models, tools, tool_load, cwd, name |
+| `ctl`         | rdwr  | Control: stop, compact, clear, inject, agent, model, models, tools, tool_load, cwd, name, systemprompt |
 | `stats`       | read  | Agent statistics (usage=, cost=, ctxsz=) |
-| `models`      | read  | Available models for current backend |
-| `systemprompt` | read | Fully rendered system prompt |
 | `tools`       | r/w   | Write tool name to load. Read: list loaded tools |
 | `proc/`       | dir   | Detached background processes |