diff --git a/session/agent.go b/session/agent.go
index 2d7098b..a06eabb 100644
--- a/session/agent.go
+++ b/session/agent.go
@@ -2,6 +2,7 @@ package session
 
 import (
 	"context"
+	"os"
 	"sync"
 	"sync/atomic"
 
@@ -50,6 +51,8 @@ type Agent struct {
 	startupMessages []string
 	readPlanStep   func() string
 	saveSession    func()       // trigger debounced persistence
+	flushSave      func()       // immediately flush persistence
+	turnError      func(ctx context.Context, errType, errMsg string) HookResult // overridable for tests
 }
 
 // Backend returns the active backend from the runtime.
@@ -181,3 +184,27 @@ func (ag *Agent) SetCwd(dir string) {
 	ag.cwd = dir
 	ag.stateMu.Unlock()
 }
+
+// effectiveCwd returns the agent's cwd, falling back to os.Getwd() if empty.
+func (ag *Agent) effectiveCwd() string {
+	if c := ag.Cwd(); c != "" {
+		return c
+	}
+	wd, _ := os.Getwd()
+	return wd
+}
+
+// IsRunning returns true if the agent has an active turn in progress.
+func (ag *Agent) IsRunning() bool {
+	return ag.currentAction.Load() != nil
+}
+
+// Interrupt cancels the current in-progress agent turn.
+// Returns true if an action was running and was cancelled.
+func (ag *Agent) Interrupt(cause error) bool {
+	if h := ag.currentAction.Load(); h != nil {
+		h.cancel(cause)
+		return true
+	}
+	return false
+}
diff --git a/session/commands.go b/session/commands.go
index df31c00..9dcaa2d 100644
--- a/session/commands.go
+++ b/session/commands.go
@@ -215,9 +215,9 @@ func (a *Session) handleCommand(ctx context.Context, input string) bool {
 				return
 			}
 			snapshot := a.r.history.PreCompactionSnapshot()
-			a.setState("compacting")
-			n, err := a.runCompact(ctx, "manual")
-			a.setState("idle")
+			a.r.SetState("compacting")
+			n, err := a.r.runCompact(ctx, "manual")
+			a.r.SetState("idle")
 			if err != nil {
 				a.emit(infoEvent("compact error: " + err.Error()))
 				return
diff --git a/session/core_test.go b/session/core_test.go
index a1f7500..42cd8f3 100644
--- a/session/core_test.go
+++ b/session/core_test.go
@@ -1830,7 +1830,7 @@ func TestCore_SetGenerationParams_Success(t *testing.T) {
 func TestAutoCompactLimit_DefaultWhenZero(t *testing.T) {
 	be := &mockBackend{name: "mock", model: "test", ctxLen: 0}
 	c := newCore(t, be, nil)
-	limit := c.autoCompactLimit(context.Background())
+	limit := c.r.autoCompactLimit(context.Background())
 	want := defaultContextLength * 3 / 4
 	if limit != want {
 		t.Errorf("autoCompactLimit with ctxLen=0 = %d; want %d", limit, want)
diff --git a/session/loop_turnerror_test.go b/session/loop_turnerror_test.go
index d61fbe2..0cd4e39 100644
--- a/session/loop_turnerror_test.go
+++ b/session/loop_turnerror_test.go
@@ -36,7 +36,7 @@ func TestTurnError_HookInterceptsRateLimit(t *testing.T) {
 	be.respond = errStream(&backend.RateLimitError{Message: "quota exceeded"})
 
 	c := newCore(t, be, nil)
-	c.turnError = func(_ context.Context, errType, _ string) HookResult {
+	c.r.turnError = func(_ context.Context, errType, _ string) HookResult {
 		atomic.AddInt32(&hookCalls, 1)
 		if errType != "rate_limit" {
 			t.Errorf("errType = %q; want rate_limit", errType)
@@ -63,7 +63,7 @@ func TestTurnError_HookInterceptsToolUnsupported(t *testing.T) {
 	be.respond = errStream(&backend.ToolUnsupportedError{Message: "model does not support tools"})
 
 	c := newCore(t, be, nil)
-	c.turnError = func(_ context.Context, errType, _ string) HookResult {
+	c.r.turnError = func(_ context.Context, errType, _ string) HookResult {
 		atomic.AddInt32(&hookCalls, 1)
 		if errType != "tool_unsupported" {
 			t.Errorf("errType = %q; want tool_unsupported", errType)
@@ -111,7 +111,7 @@ func TestTurnError_NonRetryableErrorNoHook(t *testing.T) {
 	be.respond = errStream(&backend.ToolUnsupportedError{Message: "no tools"})
 
 	c := newCore(t, be, nil)
-	c.turnError = func(_ context.Context, errType, _ string) HookResult {
+	c.r.turnError = func(_ context.Context, errType, _ string) HookResult {
 		atomic.AddInt32(&hookCalls, 1)
 		return HookResult{Ran: true, Handled: true}
 	}
@@ -131,7 +131,7 @@ func TestTurnError_HookNotRunOnSuccess(t *testing.T) {
 	// Default respond returns textStream("ok") — no error.
 
 	c := newCore(t, be, nil)
-	c.turnError = func(_ context.Context, _, _ string) HookResult {
+	c.r.turnError = func(_ context.Context, _, _ string) HookResult {
 		atomic.AddInt32(&hookCalls, 1)
 		return HookResult{Ran: true}
 	}
diff --git a/session/session.go b/session/session.go
index f6ca25a..85bf4c5 100644
--- a/session/session.go
+++ b/session/session.go
@@ -9,7 +9,6 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"runtime/debug"
 	"slices"
 	"strconv"
 	"strings"
@@ -321,7 +320,6 @@ type Session struct {
 	log             *olog.Logger
 	sessionsDir     string
 	listHandlers    map[string]func() []string
-	turnError       func(ctx context.Context, errType, errMsg string) HookResult // overridable for tests
 	remote          string   // SSH target for remote execution
 	mu              sync.RWMutex
 	auditLog        *olog.Logger
@@ -486,17 +484,9 @@ func New(cfg Config) *Session {
 	}
 	a.r.InitCond()
 	a.r.state = "idle"
-	a.turnError = func(_ context.Context, errType, errMsg string) HookResult {
-		hookCtx, cancel := context.WithTimeout(context.Background(), time.Duration(hookTimeout)*time.Second)
-		defer cancel()
-		return a.r.runtime.Hooks.Run(hookCtx, HookTurnError, map[string]string{
-			"session_id": a.id,
-			"cwd":        a.CWD(),
-			"model":      a.r.runtime.Backend.Model(),
-			"error_type": errType,
-			"error":      errMsg,
-		}, a.log)
-	}
+	a.r.flushSave = a.flushSave
+	a.r.saveSession = a.saveSession
+	a.r.turnError = a.r.defaultTurnError
 	a.pushSessionEnv()
 	a.pushLockDir()
 	return a
@@ -850,97 +840,6 @@ func (a *Session) SetSessionID(newID string) error {
 const defaultContextLength = 128000
 const defaultToolResultMaxBytes = 131072
 
-// autoCompactLimit returns the token threshold for auto-compaction (75%).
-func (a *Session) autoCompactLimit(ctx context.Context) int {
-	ctxLen := a.r.runtime.Backend.ContextLength(ctx)
-	if ctxLen <= 0 {
-		ctxLen = defaultContextLength
-	}
-	return ctxLen * 3 / 4
-}
-
-// autoWarnLimit returns the token threshold for a context-usage warning (60%).
-func (a *Session) autoWarnLimit(ctx context.Context) int {
-	ctxLen := a.r.runtime.Backend.ContextLength(ctx)
-	if ctxLen <= 0 {
-		ctxLen = defaultContextLength
-	}
-	return ctxLen * 3 / 5
-}
-
-// spawnContext assembles the agent context injected at each session refresh
-// point (session start, post-clear, post-compaction). It combines the
-// agent-specific prompt with any agentSpawn hook output.
-func (a *Session) spawnContext(ctx context.Context) string {
-	result := a.r.runtime.Hooks.Run(ctx, HookAgentSpawn, map[string]string{
-		"session_id": a.id,
-		"agent":      a.r.agentName,
-		"cwd":        a.CWD(),
-		"model":      a.r.runtime.Backend.Model(),
-	}, a.log)
-	if result.Warning != "" {
-		a.emit(infoEvent(result.Warning))
-	}
-	if sum := result.Summary(); sum != "" {
-		a.emit(infoEvent("agentSpawn: " + sum))
-	}
-	var parts []string
-	if result.Context != "" {
-		parts = append(parts, result.Context)
-	}
-	return strings.Join(parts, "\n\n---\n\n")
-}
-
-// runCompact executes a full compaction cycle: pre-hook, compact, spawn-context
-// re-injection, post-hook. Returns (n compacted, error). Returns (0, nil) if
-// the pre-hook blocked or there was nothing to compact. Caller manages setState.
-func (a *Session) runCompact(ctx context.Context, trigger string) (int, error) {
-	payload := map[string]string{"session_id": a.id, "trigger": trigger, "cwd": a.CWD()}
-	pre := a.r.runtime.Hooks.Run(ctx, HookPreCompact, payload, a.log)
-	if pre.Warning != "" {
-		a.emit(infoEvent(pre.Warning))
-	}
-	if sum := pre.Summary(); sum != "" {
-		a.emit(infoEvent("preCompact: " + sum))
-	}
-	if pre.Blocked {
-		a.emit(infoEvent("compact cancelled by hook"))
-		return 0, nil
-	}
-	if pre.Context != "" {
-		a.r.history.appendUserMessage(pre.Context)
-	}
-	// Use a cheaper model for compaction if configured.
-	compactModel := resolveCompactionModel(a.r.runtime.CompactionModel, a.r.runtime.Backend)
-	origModel := a.r.runtime.Backend.Model()
-	if compactModel != "" && compactModel != origModel {
-		a.r.runtime.Backend.SetModel(compactModel)
-		defer a.r.runtime.Backend.SetModel(origModel)
-	}
-	n, _, err := a.r.history.compact(ctx, a.r.runtime.Backend)
-	if err != nil {
-		return 0, err
-	}
-	if n > 0 {
-		a.auditLog.Debug("compact: removed %d messages trigger=%s session=%s", n, trigger, a.id)
-		a.r.warnedContext = false
-		if sc := a.spawnContext(ctx); sc != "" {
-			a.r.history.appendUserMessage(sc)
-		}
-	}
-	post := a.r.runtime.Hooks.Run(ctx, HookPostCompact, payload, a.log)
-	if post.Warning != "" {
-		a.emit(infoEvent(post.Warning))
-	}
-	if sum := post.Summary(); sum != "" {
-		a.emit(infoEvent("postCompact: " + sum))
-	}
-	if post.Context != "" {
-		a.r.history.appendUserMessage(post.Context)
-	}
-	return n, nil
-}
-
 func (a *Session) activeSessionPath(id, suffix string) string {
 	return filepath.Join(a.sessionsDir, "active", id+suffix)
 }
@@ -993,22 +892,11 @@ func (a *Session) SaveSession(path string) error {
 		a.r.runtime.Backend.Name(), a.r.runtime.Backend.Model(), a.CWD(), a.remote)
 }
 
-func (a *Session) getActionCancel() context.CancelCauseFunc {
-	if a := a.r.currentAction.Load(); a != nil {
-		return a.cancel
-	}
-	return nil
-}
-
 // Interrupt cancels the current in-progress agent turn.
 // Returns true if an action was running and was cancelled.
 func (a *Session) Interrupt(cause error) bool {
 	a.log.Debug("Interrupt() cause=%v", cause)
-	if cancel := a.getActionCancel(); cancel != nil {
-		cancel(cause)
-		return true
-	}
-	return false
+	return a.r.Interrupt(cause)
 }
 
 func (a *Session) Inject(prompt string) {
@@ -1052,7 +940,7 @@ func (a *Session) PopQueue() (string, bool) {
 }
 
 func (a *Session) IsRunning() bool {
-	v := a.r.currentAction.Load() != nil
+	v := a.r.IsRunning()
 	a.log.Debug("IsRunning() = %v", v)
 	return v
 }
@@ -1167,357 +1055,32 @@ func firstSentence(s string) string {
 	return s
 }
 
-// Submit implements Core. It processes one line of user input: slash commands
-// and shell shortcuts are dispatched immediately; any other input
-// starts an agent turn that streams events to the bus. If a turn is already
-// in progress the prompt is queued as an in-stream interruption instead.
-//
-// Continuations (post-turn hook context, unconsumed inject, FIFO drain) are
-// handled via an explicit loop rather than recursion to avoid stack growth.
+// Submit processes one line of user input: slash commands are dispatched
+// immediately; any other input is delegated to the agent for turn execution.
 func (a *Session) Submit(ctx context.Context, input string) {
-	defer func() {
-		if r := recover(); r != nil {
-			a.log.Error("panic: %v\n%s", r, debug.Stack())
-			if a := a.r.currentAction.Swap(nil); a != nil {
-				a.cancel(fmt.Errorf("%v", r))
-			}
-			a.r.SetState("idle")
-			a.emit(Event{Role: "error", Content: fmt.Sprintf("%v", r)})
-		}
-	}()
 	a.log.Debug("Submit() input_len=%d running=%v", len(input), a.IsRunning())
 	if input == "" {
 		return
 	}
 
-	// Fast path: inject and FIFO push use atomics and are safe without
-	// the submit lock. Handle them before acquiring submitMu so they
-	// don't block behind a long-running turn or command.
+	// Commands are handled at the session level (they reference sessionsDir,
+	// listHandlers, etc.). If the input is a command, handle it and return.
 	if a.IsRunning() {
 		if a.handleCommand(ctx, input) {
 			return
 		}
-		a.r.fifo.Push(input)
-		return
-	}
-
-	// Serialize commands and turns so that e.g. a /compact arriving via
-	// ctl cannot race with an executeTurn arriving via prompt.
-	a.r.submitMu.Lock()
-	defer a.r.submitMu.Unlock()
-
-	if a.handleCommand(ctx, input) {
-		return
-	}
-	if a.IsRunning() {
-		a.r.fifo.Push(input)
-		return
-	}
-
-	for input != "" && ctx.Err() == nil {
-		input = a.executeTurn(ctx, input)
-	}
-}
-
-// executeTurn runs a single agent turn and returns the next prompt to execute,
-// or "" if there is nothing more to do.
-func (a *Session) executeTurn(ctx context.Context, input string) string {
-	a.emit(Event{Role: "user", Content: input})
-
-	hookResult := a.r.runtime.Hooks.Run(ctx, HookPreTurn, map[string]string{
-		"session_id": a.id,
-		"cwd":        a.CWD(),
-		"prompt":     input,
-	}, a.log)
-	if hookResult.Blocked {
-		a.emit(infoEvent("hook blocked prompt"))
-		return ""
-	}
-	if hookResult.Warning != "" {
-		a.emit(infoEvent(hookResult.Warning))
-	}
-	if sum := hookResult.Summary(); sum != "" {
-		a.emit(infoEvent("preTurn: " + sum))
-	}
-	if hookResult.Context != "" {
-		input += "\n" + hookResult.Context
-	}
-
-	// Snapshot session state before this turn modifies it. Restored on failure
-	// so the session is clean for the next attempt.
-	snapSession := a.r.history
-	var snapMessages []backend.Message
-	if a.r.history != nil {
-		snapMessages = cloneMessages(a.r.history.messages)
-	}
-
-	if a.r.history == nil {
-		for _, msg := range a.r.startupMessages {
-			a.log.Debug("startup: %s", msg)
-			a.emit(infoEvent(msg))
-		}
-		a.r.startupMessages = nil
-		a.r.history = newHistory(input)
-		if sc := a.spawnContext(ctx); sc != "" {
-			a.r.history.appendUserMessage(sc)
-		}
-		a.r.history.appendUserMessage(input)
 	} else {
-		a.r.history.appendUserMessage(input)
-	}
-
-	actCtx, actCancel := context.WithCancelCause(ctx)
-	handle := &actionHandle{cancel: actCancel}
-	a.r.currentAction.Store(handle)
-	a.r.SetState("thinking")
-
-	a.auditLog.Debug("turn: start input=%s session=%s", auditTruncate(input), a.id)
-
-	// Build per-turn agentConfig from the current runtime.
-	a.r.cfg = agentConfig{
-		Backend:          a.r.runtime.Backend,
-		preamble:         a.r.runtime.Preamble,
-		Tools:            a.r.runtime.Tools,
-		Exec:             a.r.runtime.Exec,
-		ClassifyTool:     a.r.runtime.ClassifyTool,
-		ClassifyTier:     a.r.runtime.ClassifyTier,
-		GenerationParams: a.r.runtime.GenParams,
-		MaxSteps:         a.r.runtime.MaxSteps,
-		ReadPlanStep:     a.r.readPlanStep,
-		TurnError:        a.turnError,
-	}
-
-	var replyBuf strings.Builder
-	a.r.cfg.Output = func(ev Event) {
-		switch ev.Role {
-		case "assistant":
-			replyBuf.WriteString(ev.Content)
-		case "call":
-			a.r.SetState("calling: " + ev.Name)
-			a.auditLog.Debug("call: %s %s", ev.Name, auditTruncate(string(ev.Content)))
-		case "tool":
-			a.auditLog.Debug("result: %s %s", ev.Name, auditTruncate(ev.Content))
-		case "state":
-			a.r.SetState(ev.Content)
-		case "limitretry":
-			a.r.SetState("limitretry")
-		case "error":
-			a.auditLog.Debug("error: %s", ev.Content)
-		}
-		if ev.Role == "usage" && a.r.history != nil {
-			var in, out, est, cached, creation int
-			var costUSD float64
-			fmt.Sscanf(ev.Content, "%d %d %d %g %d %d", &in, &out, &est, &costUSD, &cached, &creation)
-			a.r.history.addUsage(backend.Usage{
-				InputTokens:         in,
-				CachedInputTokens:   cached,
-				CacheCreationTokens: creation,
-				OutputTokens:        out,
-				CostUSD:             costUSD,
-			}, est != 0)
-			a.r.notifyChange()
-			if maxCostStr := os.Getenv("OLLIE_MAX_SESSION_COST"); maxCostStr != "" {
-				if limit, ferr := strconv.ParseFloat(maxCostStr, 64); ferr == nil && limit > 0 && a.r.history.SessionCostUSD >= limit {
-					a.emit(infoEvent(fmt.Sprintf("spending cap $%.2f reached — stopping", limit)))
-					a.Interrupt(ErrInterrupted)
-				}
-			}
-		}
-		a.emit(ev)
-	}
-	a.r.cfg.PopInject = func() string {
-		if p := a.r.pendingInject.Swap(nil); p != nil {
-			return *p
-		}
-		return ""
-	}
-	a.r.cfg.PreTool = func(ctx context.Context, name string, args json.RawMessage) HookResult {
-		return a.r.runtime.Hooks.Run(ctx, HookPreTool, map[string]string{
-			"session_id": a.id,
-			"cwd":        a.CWD(),
-			"tool":       name,
-			"args":       string(args),
-		}, a.log)
-	}
-	a.r.cfg.PostTool = func(ctx context.Context, name string, args json.RawMessage, result string) HookResult {
-		return a.r.runtime.Hooks.Run(ctx, HookPostTool, map[string]string{
-			"session_id": a.id,
-			"cwd":        a.CWD(),
-			"tool":       name,
-			"args":       string(args),
-			"result":     result,
-		}, a.log)
-	}
-	a.r.cfg.IncrToolCallCount = func() int64 {
-		return a.r.toolCallCount.Add(1)
-	}
-	a.r.cfg.SaveSession = func() { a.saveSession() }
-	a.r.cfg.ResultCache = &a.r.resultCache
-	a.r.cfg.AutoCompact = func(ctx context.Context) {
-		if ctx.Err() != nil || a.r.history == nil {
+		// Serialize commands with turns — acquire submitMu to check.
+		a.r.submitMu.Lock()
+		if a.handleCommand(ctx, input) {
+			a.r.submitMu.Unlock()
 			return
 		}
-		limit := a.autoCompactLimit(ctx)
-		if limit <= 0 || a.r.history.estimateTokens() < limit {
-			return
-		}
-		a.emit(Event{Role: "info", Content: "auto-compacting context...\n"})
-		a.r.SetState("compacting")
-		if _, err := a.runCompact(ctx, "auto"); err != nil {
-			panic(fmt.Sprintf("mid-turn auto-compact: %v", err))
-		}
-		a.r.SetState("thinking")
+		a.r.submitMu.Unlock()
 	}
 
-	// Warn once when context usage crosses 60%; compact at 75%.
-	if a.r.history != nil {
-		tokens := a.r.history.estimateTokens()
-		if compactLimit := a.autoCompactLimit(ctx); compactLimit > 0 && tokens >= compactLimit {
-			a.emit(Event{Role: "info", Content: "auto-compacting context...\n"})
-			a.r.SetState("compacting")
-			if _, err := a.runCompact(ctx, "auto"); err != nil {
-				panic(fmt.Sprintf("auto-compact: %v", err))
-			}
-			a.r.SetState("thinking")
-		} else if warnLimit := a.autoWarnLimit(ctx); warnLimit > 0 && tokens >= warnLimit && !a.r.warnedContext {
-			ctxLen := a.r.cfg.Backend.ContextLength(ctx)
-			if ctxLen <= 0 {
-				ctxLen = defaultContextLength
-			}
-			pct := tokens * 100 / ctxLen
-			a.emit(Event{Role: "info", Content: fmt.Sprintf("context at %d%% — will auto-compact at 75%%\n", pct)})
-			a.r.warnedContext = true
-		}
-	}
-
-	// Spending cap: reject before spending more tokens.
-	if maxCostStr := os.Getenv("OLLIE_MAX_SESSION_COST"); maxCostStr != "" && a.r.history != nil {
-		if limit, err := strconv.ParseFloat(maxCostStr, 64); err == nil && limit > 0 {
-			if a.r.history.SessionCostUSD >= limit {
-				a.emit(Event{Role: "error", Content: fmt.Sprintf("spending cap $%.2f reached (session total $%.4f)", limit, a.r.history.SessionCostUSD)})
-				a.r.SetState("idle")
-				actCancel(nil)
-				a.r.currentAction.CompareAndSwap(handle, nil)
-				if snapSession == nil {
-					a.r.history = nil
-				} else {
-					a.r.history.messages = snapMessages
-				}
-				return ""
-			}
-		}
-	}
-
-	if a.r.history != nil {
-		a.r.history.resetTurnAccumulators()
-	}
-
-	// Run the turn, retrying once after compaction on context overflow.
-	var (
-		overflowRetried bool
-		err             error
-	)
-	for {
-		err = run(actCtx, a.r.cfg, a.r.history)
-		actCancel(nil)
-		a.r.currentAction.CompareAndSwap(handle, nil)
-
-		if err == nil {
-			break
-		}
-		if errors.Is(err, context.Canceled) || errors.Is(err, ErrInterrupted) {
-			break
-		}
-		var ctxErr *backend.ContextOverflowError
-		if !overflowRetried && errors.As(err, &ctxErr) && a.r.history != nil {
-			overflowRetried = true
-			a.r.history.messages = snapMessages
-			a.emit(Event{Role: "info", Content: "context overflow — compacting and retrying...\n"})
-			a.r.SetState("compacting")
-			if _, cerr := a.runCompact(ctx, "overflow"); cerr != nil {
-				break
-			}
-			a.r.history.appendUserMessage(input)
-			a.r.SetState("thinking")
-			a.r.history.resetTurnAccumulators()
-			replyBuf.Reset()
-			actCtx, actCancel = context.WithCancelCause(ctx)
-			handle = &actionHandle{cancel: actCancel}
-			a.r.currentAction.Store(handle)
-			continue
-		}
-		break
-	}
-
-	a.mu.Lock()
-	a.r.SetReply(replyBuf.String())
-	a.mu.Unlock()
-	replyBuf.Reset()
-	a.r.SetState("idle")
-	a.flushSave()
-
-	if err != nil {
-		// Keep completed work — only remove cancelled tool results.
-		// Error results are valuable feedback for the agent.
-		if a.r.history != nil {
-			a.r.history.removeCancelledToolResults()
-		}
-		if errors.Is(err, context.Canceled) || errors.Is(err, ErrInterrupted) {
-			a.auditLog.Debug("turn: interrupted session=%s", a.id)
-			a.saveSession()
-			return ""
-		}
-		a.emit(Event{Role: "error", Content: err.Error()})
-		// Drain one FIFO item — the turnError hook may have queued a recovery prompt.
-		if next, ok := a.r.fifo.Pop(); ok {
-			return next
-		}
-		return ""
-	}
-
-	stopResult := a.r.runtime.Hooks.Run(ctx, HookPostTurn, map[string]string{
-		"session_id": a.id,
-		"cwd":        a.CWD(),
-	}, a.log)
-	if stopResult.Warning != "" {
-		a.emit(infoEvent(stopResult.Warning))
-	}
-	if sum := stopResult.Summary(); sum != "" {
-		a.emit(infoEvent("postTurn: " + sum))
-	}
-	if !stopResult.Blocked && stopResult.Context != "" && a.r.history != nil {
-		a.r.history.appendUserMessage(stopResult.Context)
-	}
-
-	if a.r.history != nil {
-		a.r.history.recordTurnCost(a.r.cfg.Backend.Model())
-		appendUsageLog(a.id, a.r.cfg.Backend.Name(), a.r.cfg.Backend.Model(), a.r.history)
-		if a.r.history.LastTurnCostUSD > 0 {
-			a.emit(Event{Role: "info", Content: fmt.Sprintf("costLast=$%.4f\n", a.r.history.LastTurnCostUSD)})
-		}
-		a.auditLog.Debug("turn: end reply=%s cost=$%.4f session_total=$%.4f session=%s",
-			auditTruncate(a.r.Reply()), a.r.history.LastTurnCostUSD, a.r.history.SessionCostUSD, a.id)
-		a.r.notifyChange()
-	}
-	a.saveSession()
-
-	// Post-turn hook said "continue" — its context becomes the next prompt.
-	if stopResult.Blocked && stopResult.Context != "" {
-		return stopResult.Context
-	}
-
-	// Inject that was pending but never consumed (text-only response with no
-	// tool calls) — treat it as the next user message.
-	if p := a.r.pendingInject.Swap(nil); p != nil {
-		return *p
-	}
-
-	// Drain one item from the FIFO; the outer loop handles the rest.
-	if next, ok := a.r.fifo.Pop(); ok {
-		return next
-	}
-
-	return ""
+	// Delegate to the agent for turn execution (or FIFO queueing if running).
+	a.r.Submit(ctx, input)
 }
 
 func toolInfosToBackend(infos []tools.ToolInfo) []backend.Tool {
diff --git a/session/turn.go b/session/turn.go
new file mode 100644
index 0000000..3da5ee9
--- /dev/null
+++ b/session/turn.go
@@ -0,0 +1,466 @@
+package session
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"runtime/debug"
+	"strconv"
+	"strings"
+	"time"
+
+	"ollie/backend"
+)
+
+// Submit processes one line of user input: it starts an agent turn that streams
+// events to the bus. If a turn is already in progress the prompt is queued as
+// an in-stream interruption instead.
+//
+// Slash commands are NOT handled here — the caller (Session.Submit) dispatches
+// those before delegating to Agent.Submit.
+//
+// Continuations (post-turn hook context, unconsumed inject, FIFO drain) are
+// handled via an explicit loop rather than recursion to avoid stack growth.
+func (ag *Agent) Submit(ctx context.Context, input string) {
+	defer func() {
+		if r := recover(); r != nil {
+			ag.log.Error("panic: %v\n%s", r, debug.Stack())
+			if a := ag.currentAction.Swap(nil); a != nil {
+				a.cancel(fmt.Errorf("%v", r))
+			}
+			ag.SetState("idle")
+			ag.emit(Event{Role: "error", Content: fmt.Sprintf("%v", r)})
+		}
+	}()
+	ag.log.Debug("Agent.Submit() input_len=%d running=%v", len(input), ag.IsRunning())
+	if input == "" {
+		return
+	}
+
+	if ag.IsRunning() {
+		ag.fifo.Push(input)
+		return
+	}
+
+	// Serialize turns so that e.g. a /compact arriving via ctl cannot race
+	// with an executeTurn arriving via prompt.
+	ag.submitMu.Lock()
+	defer ag.submitMu.Unlock()
+
+	if ag.IsRunning() {
+		ag.fifo.Push(input)
+		return
+	}
+
+	for input != "" && ctx.Err() == nil {
+		input = ag.executeTurn(ctx, input)
+	}
+}
+
+// executeTurn runs a single agent turn and returns the next prompt to execute,
+// or "" if there is nothing more to do.
+func (ag *Agent) executeTurn(ctx context.Context, input string) string {
+	ag.emit(Event{Role: "user", Content: input})
+
+	hookResult := ag.runtime.Hooks.Run(ctx, HookPreTurn, map[string]string{
+		"session_id": ag.sessionID,
+		"cwd":        ag.effectiveCwd(),
+		"prompt":     input,
+	}, ag.log)
+	if hookResult.Blocked {
+		ag.emit(infoEvent("hook blocked prompt"))
+		return ""
+	}
+	if hookResult.Warning != "" {
+		ag.emit(infoEvent(hookResult.Warning))
+	}
+	if sum := hookResult.Summary(); sum != "" {
+		ag.emit(infoEvent("preTurn: " + sum))
+	}
+	if hookResult.Context != "" {
+		input += "\n" + hookResult.Context
+	}
+
+	// Snapshot session state before this turn modifies it. Restored on failure
+	// so the session is clean for the next attempt.
+	snapSession := ag.history
+	var snapMessages []backend.Message
+	if ag.history != nil {
+		snapMessages = cloneMessages(ag.history.messages)
+	}
+
+	if ag.history == nil {
+		for _, msg := range ag.startupMessages {
+			ag.log.Debug("startup: %s", msg)
+			ag.emit(infoEvent(msg))
+		}
+		ag.startupMessages = nil
+		ag.history = newHistory(input)
+		if sc := ag.spawnContext(ctx); sc != "" {
+			ag.history.appendUserMessage(sc)
+		}
+		ag.history.appendUserMessage(input)
+	} else {
+		ag.history.appendUserMessage(input)
+	}
+
+	actCtx, actCancel := context.WithCancelCause(ctx)
+	handle := &actionHandle{cancel: actCancel}
+	ag.currentAction.Store(handle)
+	ag.SetState("thinking")
+
+	ag.auditLog.Debug("turn: start input=%s session=%s", auditTruncate(input), ag.sessionID)
+
+	// Build per-turn agentConfig from the current runtime.
+	ag.cfg = agentConfig{
+		Backend:          ag.runtime.Backend,
+		preamble:         ag.runtime.Preamble,
+		Tools:            ag.runtime.Tools,
+		Exec:             ag.runtime.Exec,
+		ClassifyTool:     ag.runtime.ClassifyTool,
+		ClassifyTier:     ag.runtime.ClassifyTier,
+		GenerationParams: ag.runtime.GenParams,
+		MaxSteps:         ag.runtime.MaxSteps,
+		ReadPlanStep:     ag.readPlanStep,
+		TurnError:        ag.turnError,
+	}
+
+	var replyBuf strings.Builder
+	ag.cfg.Output = func(ev Event) {
+		switch ev.Role {
+		case "assistant":
+			replyBuf.WriteString(ev.Content)
+		case "call":
+			ag.SetState("calling: " + ev.Name)
+			ag.auditLog.Debug("call: %s %s", ev.Name, auditTruncate(string(ev.Content)))
+		case "tool":
+			ag.auditLog.Debug("result: %s %s", ev.Name, auditTruncate(ev.Content))
+		case "state":
+			ag.SetState(ev.Content)
+		case "limitretry":
+			ag.SetState("limitretry")
+		case "error":
+			ag.auditLog.Debug("error: %s", ev.Content)
+		}
+		if ev.Role == "usage" && ag.history != nil {
+			var in, out, est, cached, creation int
+			var costUSD float64
+			fmt.Sscanf(ev.Content, "%d %d %d %g %d %d", &in, &out, &est, &costUSD, &cached, &creation)
+			ag.history.addUsage(backend.Usage{
+				InputTokens:         in,
+				CachedInputTokens:   cached,
+				CacheCreationTokens: creation,
+				OutputTokens:        out,
+				CostUSD:             costUSD,
+			}, est != 0)
+			ag.notifyChange()
+			if maxCostStr := os.Getenv("OLLIE_MAX_SESSION_COST"); maxCostStr != "" {
+				if limit, ferr := strconv.ParseFloat(maxCostStr, 64); ferr == nil && limit > 0 && ag.history.SessionCostUSD >= limit {
+					ag.emit(infoEvent(fmt.Sprintf("spending cap $%.2f reached — stopping", limit)))
+					ag.Interrupt(ErrInterrupted)
+				}
+			}
+		}
+		ag.emit(ev)
+	}
+	ag.cfg.PopInject = func() string {
+		if p := ag.pendingInject.Swap(nil); p != nil {
+			return *p
+		}
+		return ""
+	}
+	ag.cfg.PreTool = func(ctx context.Context, name string, args json.RawMessage) HookResult {
+		return ag.runtime.Hooks.Run(ctx, HookPreTool, map[string]string{
+			"session_id": ag.sessionID,
+			"cwd":        ag.effectiveCwd(),
+			"tool":       name,
+			"args":       string(args),
+		}, ag.log)
+	}
+	ag.cfg.PostTool = func(ctx context.Context, name string, args json.RawMessage, result string) HookResult {
+		return ag.runtime.Hooks.Run(ctx, HookPostTool, map[string]string{
+			"session_id": ag.sessionID,
+			"cwd":        ag.effectiveCwd(),
+			"tool":       name,
+			"args":       string(args),
+			"result":     result,
+		}, ag.log)
+	}
+	ag.cfg.IncrToolCallCount = func() int64 {
+		return ag.toolCallCount.Add(1)
+	}
+	ag.cfg.SaveSession = func() { ag.saveSession() }
+	ag.cfg.ResultCache = &ag.resultCache
+	ag.cfg.AutoCompact = func(ctx context.Context) {
+		if ctx.Err() != nil || ag.history == nil {
+			return
+		}
+		limit := ag.autoCompactLimit(ctx)
+		if limit <= 0 || ag.history.estimateTokens() < limit {
+			return
+		}
+		ag.emit(Event{Role: "info", Content: "auto-compacting context...\n"})
+		ag.SetState("compacting")
+		if _, err := ag.runCompact(ctx, "auto"); err != nil {
+			panic(fmt.Sprintf("mid-turn auto-compact: %v", err))
+		}
+		ag.SetState("thinking")
+	}
+
+	// Warn once when context usage crosses 60%; compact at 75%.
+	if ag.history != nil {
+		tokens := ag.history.estimateTokens()
+		if compactLimit := ag.autoCompactLimit(ctx); compactLimit > 0 && tokens >= compactLimit {
+			ag.emit(Event{Role: "info", Content: "auto-compacting context...\n"})
+			ag.SetState("compacting")
+			if _, err := ag.runCompact(ctx, "auto"); err != nil {
+				panic(fmt.Sprintf("auto-compact: %v", err))
+			}
+			ag.SetState("thinking")
+		} else if warnLimit := ag.autoWarnLimit(ctx); warnLimit > 0 && tokens >= warnLimit && !ag.warnedContext {
+			ctxLen := ag.cfg.Backend.ContextLength(ctx)
+			if ctxLen <= 0 {
+				ctxLen = defaultContextLength
+			}
+			pct := tokens * 100 / ctxLen
+			ag.emit(Event{Role: "info", Content: fmt.Sprintf("context at %d%% — will auto-compact at 75%%\n", pct)})
+			ag.warnedContext = true
+		}
+	}
+
+	// Spending cap: reject before spending more tokens.
+	if maxCostStr := os.Getenv("OLLIE_MAX_SESSION_COST"); maxCostStr != "" && ag.history != nil {
+		if limit, err := strconv.ParseFloat(maxCostStr, 64); err == nil && limit > 0 {
+			if ag.history.SessionCostUSD >= limit {
+				ag.emit(Event{Role: "error", Content: fmt.Sprintf("spending cap $%.2f reached (session total $%.4f)", limit, ag.history.SessionCostUSD)})
+				ag.SetState("idle")
+				actCancel(nil)
+				ag.currentAction.CompareAndSwap(handle, nil)
+				if snapSession == nil {
+					ag.history = nil
+				} else {
+					ag.history.messages = snapMessages
+				}
+				return ""
+			}
+		}
+	}
+
+	if ag.history != nil {
+		ag.history.resetTurnAccumulators()
+	}
+
+	// Run the turn, retrying once after compaction on context overflow.
+	var (
+		overflowRetried bool
+		err             error
+	)
+	for {
+		err = run(actCtx, ag.cfg, ag.history)
+		actCancel(nil)
+		ag.currentAction.CompareAndSwap(handle, nil)
+
+		if err == nil {
+			break
+		}
+		if errors.Is(err, context.Canceled) || errors.Is(err, ErrInterrupted) {
+			break
+		}
+		var ctxErr *backend.ContextOverflowError
+		if !overflowRetried && errors.As(err, &ctxErr) && ag.history != nil {
+			overflowRetried = true
+			ag.history.messages = snapMessages
+			ag.emit(Event{Role: "info", Content: "context overflow — compacting and retrying...\n"})
+			ag.SetState("compacting")
+			if _, cerr := ag.runCompact(ctx, "overflow"); cerr != nil {
+				break
+			}
+			ag.history.appendUserMessage(input)
+			ag.SetState("thinking")
+			ag.history.resetTurnAccumulators()
+			replyBuf.Reset()
+			actCtx, actCancel = context.WithCancelCause(ctx)
+			handle = &actionHandle{cancel: actCancel}
+			ag.currentAction.Store(handle)
+			continue
+		}
+		break
+	}
+
+	ag.SetReply(replyBuf.String())
+	replyBuf.Reset()
+	ag.SetState("idle")
+	if ag.flushSave != nil {
+		ag.flushSave()
+	}
+
+	if err != nil {
+		// Keep completed work — only remove cancelled tool results.
+		if ag.history != nil {
+			ag.history.removeCancelledToolResults()
+		}
+		if errors.Is(err, context.Canceled) || errors.Is(err, ErrInterrupted) {
+			ag.auditLog.Debug("turn: interrupted session=%s", ag.sessionID)
+			ag.saveSession()
+			return ""
+		}
+		ag.emit(Event{Role: "error", Content: err.Error()})
+		// Drain one FIFO item — the turnError hook may have queued a recovery prompt.
+		if next, ok := ag.fifo.Pop(); ok {
+			return next
+		}
+		return ""
+	}
+
+	stopResult := ag.runtime.Hooks.Run(ctx, HookPostTurn, map[string]string{
+		"session_id": ag.sessionID,
+		"cwd":        ag.effectiveCwd(),
+	}, ag.log)
+	if stopResult.Warning != "" {
+		ag.emit(infoEvent(stopResult.Warning))
+	}
+	if sum := stopResult.Summary(); sum != "" {
+		ag.emit(infoEvent("postTurn: " + sum))
+	}
+	if !stopResult.Blocked && stopResult.Context != "" && ag.history != nil {
+		ag.history.appendUserMessage(stopResult.Context)
+	}
+
+	if ag.history != nil {
+		ag.history.recordTurnCost(ag.cfg.Backend.Model())
+		appendUsageLog(ag.sessionID, ag.cfg.Backend.Name(), ag.cfg.Backend.Model(), ag.history)
+		if ag.history.LastTurnCostUSD > 0 {
+			ag.emit(Event{Role: "info", Content: fmt.Sprintf("costLast=$%.4f\n", ag.history.LastTurnCostUSD)})
+		}
+		ag.auditLog.Debug("turn: end reply=%s cost=$%.4f session_total=$%.4f session=%s",
+			auditTruncate(ag.Reply()), ag.history.LastTurnCostUSD, ag.history.SessionCostUSD, ag.sessionID)
+		ag.notifyChange()
+	}
+	ag.saveSession()
+
+	// Post-turn hook said "continue" — its context becomes the next prompt.
+	if stopResult.Blocked && stopResult.Context != "" {
+		return stopResult.Context
+	}
+
+	// Inject that was pending but never consumed (text-only response with no
+	// tool calls) — treat it as the next user message.
+	if p := ag.pendingInject.Swap(nil); p != nil {
+		return *p
+	}
+
+	// Drain one item from the FIFO; the outer loop handles the rest.
+	if next, ok := ag.fifo.Pop(); ok {
+		return next
+	}
+
+	return ""
+}
+
+// turnError is called on the first backend error of a turn. If the hook handles
+// the error (exit 0), the turn exits immediately.
+// This is the default implementation; it can be overridden via the turnError field.
+func (ag *Agent) defaultTurnError(ctx context.Context, errType, errMsg string) HookResult {
+	hookCtx, cancel := context.WithTimeout(context.Background(), time.Duration(hookTimeout)*time.Second)
+	defer cancel()
+	return ag.runtime.Hooks.Run(hookCtx, HookTurnError, map[string]string{
+		"session_id": ag.sessionID,
+		"cwd":        ag.effectiveCwd(),
+		"model":      ag.runtime.Backend.Model(),
+		"error_type": errType,
+		"error":      errMsg,
+	}, ag.log)
+}
+
+// autoCompactLimit returns the token threshold for auto-compaction (75%).
+func (ag *Agent) autoCompactLimit(ctx context.Context) int {
+	ctxLen := ag.runtime.Backend.ContextLength(ctx)
+	if ctxLen <= 0 {
+		ctxLen = defaultContextLength
+	}
+	return ctxLen * 3 / 4
+}
+
+// autoWarnLimit returns the token threshold for a context-usage warning (60%).
+func (ag *Agent) autoWarnLimit(ctx context.Context) int {
+	ctxLen := ag.runtime.Backend.ContextLength(ctx)
+	if ctxLen <= 0 {
+		ctxLen = defaultContextLength
+	}
+	return ctxLen * 3 / 5
+}
+
+// spawnContext assembles the agent context injected at each session refresh
+// point (session start, post-clear, post-compaction). It combines the
+// agent-specific prompt with any agentSpawn hook output.
+func (ag *Agent) spawnContext(ctx context.Context) string {
+	result := ag.runtime.Hooks.Run(ctx, HookAgentSpawn, map[string]string{
+		"session_id": ag.sessionID,
+		"agent":      ag.agentName,
+		"cwd":        ag.effectiveCwd(),
+		"model":      ag.runtime.Backend.Model(),
+	}, ag.log)
+	if result.Warning != "" {
+		ag.emit(infoEvent(result.Warning))
+	}
+	if sum := result.Summary(); sum != "" {
+		ag.emit(infoEvent("agentSpawn: " + sum))
+	}
+	var parts []string
+	if result.Context != "" {
+		parts = append(parts, result.Context)
+	}
+	return strings.Join(parts, "\n\n---\n\n")
+}
+
+// runCompact executes a full compaction cycle: pre-hook, compact, spawn-context
+// re-injection, post-hook. Returns (n compacted, error). Returns (0, nil) if
+// the pre-hook blocked or there was nothing to compact. Caller manages setState.
+func (ag *Agent) runCompact(ctx context.Context, trigger string) (int, error) {
+	payload := map[string]string{"session_id": ag.sessionID, "trigger": trigger, "cwd": ag.effectiveCwd()}
+	pre := ag.runtime.Hooks.Run(ctx, HookPreCompact, payload, ag.log)
+	if pre.Warning != "" {
+		ag.emit(infoEvent(pre.Warning))
+	}
+	if sum := pre.Summary(); sum != "" {
+		ag.emit(infoEvent("preCompact: " + sum))
+	}
+	if pre.Blocked {
+		ag.emit(infoEvent("compact cancelled by hook"))
+		return 0, nil
+	}
+	if pre.Context != "" {
+		ag.history.appendUserMessage(pre.Context)
+	}
+	// Use a cheaper model for compaction if configured.
+	compactModel := resolveCompactionModel(ag.runtime.CompactionModel, ag.runtime.Backend)
+	origModel := ag.runtime.Backend.Model()
+	if compactModel != "" && compactModel != origModel {
+		ag.runtime.Backend.SetModel(compactModel)
+		defer ag.runtime.Backend.SetModel(origModel)
+	}
+	n, _, err := ag.history.compact(ctx, ag.runtime.Backend)
+	if err != nil {
+		return 0, err
+	}
+	if n > 0 {
+		ag.auditLog.Debug("compact: removed %d messages trigger=%s session=%s", n, trigger, ag.sessionID)
+		ag.warnedContext = false
+		if sc := ag.spawnContext(ctx); sc != "" {
+			ag.history.appendUserMessage(sc)
+		}
+	}
+	post := ag.runtime.Hooks.Run(ctx, HookPostCompact, payload, ag.log)
+	if post.Warning != "" {
+		ag.emit(infoEvent(post.Warning))
+	}
+	if sum := post.Summary(); sum != "" {
+		ag.emit(infoEvent("postCompact: " + sum))
+	}
+	if post.Context != "" {
+		ag.history.appendUserMessage(post.Context)
+	}
+	return n, nil
+}