session: eliminate Core interface, use concrete *agent.Session

- Delete session/core.go (the consumer-defined interface)
- Change Session.Core field from interface to *agent.Session
- Change NewSession and ManagerConfig.NewCore to use concrete type
- Rewrite all tests to use real sessions with backend.Noop

The 9p layer now depends directly on the concrete type from
ollie/session. No more interface indirection. Tests exercise
real session behavior instead of stub methods.

session/core.go

@@ -1,55 +0,0 @@
-package session
-
-import (
-	"context"
-
-	"github.com/simonfxr/pubsub"
-	agent "ollie/session"
-	"ollie/backend"
-)
-
-// Core is the interface that a session implementation must satisfy.
-// Defined here (at the consumer) rather than in ollie/session so that
-// the core package exports only a concrete struct with no interface overhead.
-// Tests can substitute a lightweight stub.
-type Core interface {
-	Submit(ctx context.Context, input string)
-	Interrupt(cause error) bool
-	Inject(prompt string)
-	Queue(prompt string)
-	PopQueue() (string, bool)
-	Bus() *pubsub.Bus
-	IsRunning() bool
-	State() string
-	Reply() string
-	AgentName() string
-	BackendName() string
-	ModelName() string
-	CWD() string
-	SetCWD(dir string) error
-	SetSessionID(newID string) error
-	Context() []backend.Message
-	SystemPrompt() string
-	GenerationParams() backend.GenerationParams
-	SetGenerationParams(params backend.GenerationParams) error
-	CompactionModel() string
-	SetCompactionModel(model string)
-	Usage() string
-	Cost() string
-	CtxSz() string
-	ListModels() string
-	WaitChange(ctx context.Context, field, current string) (string, bool)
-	SaveSession(path string) error
-	Close()
-	Detach() bool
-	ListDetached() []agent.DetachedInfo
-	SignalDetached(pid, signal int) error
-	GetDetachedOutput(pid int) (string, error)
-	DismissDetached(pid int) bool
-	InjectSystemEvent(content string)
-	React(emoji string)
-	ReactTo(responseID, emoji string) error
-	Reactions() map[string]string
-	ToolCallCount() int64
-	SetEnv(key, value string)
-}

session/session.go

@@ -29,7 +29,7 @@ type Session struct {
 	mu         sync.RWMutex
 	id         string
 	uname      string // immutable user principal (numeric UID), set at creation
-	Core       Core
+	Core       *agent.Session
 	Ctx        context.Context
 	cancel     context.CancelFunc
 	log        []byte
@@ -46,7 +46,7 @@ type Session struct {
 	modelsCacheAt time.Time
 }
 
-func NewSession(id string, core Core, ctx context.Context, cancel context.CancelFunc) *Session {
+func NewSession(id string, core *agent.Session, ctx context.Context, cancel context.CancelFunc) *Session {
 	sess := &Session{id: id, Core: core, Ctx: ctx, cancel: cancel}
 	sess.startEventLog()
 	return sess
@@ -235,8 +235,8 @@ type ManagerConfig struct {
 	ReadFile    func(string) ([]byte, error)
 	MkdirAll    func(string, os.FileMode) error
 	// NewCore, if non-nil, replaces the default backend.New + agent.New
-	// path. It receives the session ID, agent name, and cwd, and returns a Core.
+	// path. It receives the session ID, agent name, and cwd, and returns a Session.
-	NewCore func(sessionID, agentName, cwd string) (Core, error)
+	NewCore func(sessionID, agentName, cwd string) (*agent.Session, error)
 	// Strict rejects inline code steps; only tool steps are allowed.
 	Strict bool
 	// Yolo skips the landrun sandbox.
@@ -1122,7 +1122,7 @@ func (s *Manager) CreateSession(args []string) (string, error) {
 		return "", fmt.Errorf("session already exists: %s", sessID)
 	}
 
-	var core Core
+	var core *agent.Session
 	var sessPtr *Session
 	uname := s.nextUname()
 	if s.cfg.NewCore != nil {