lash-core 0.1.0-alpha.1

Sans-IO turn machine and runtime kernel for the lash agent runtime.
Documentation
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
use super::*;

fn trace_fields_from_outcome(
    outcome: &TurnOutcome,
) -> (&'static str, &'static str, Option<lash_trace::TraceHandoff>) {
    match outcome {
        TurnOutcome::Finished(TurnFinish::AssistantMessage { .. }) => {
            ("completed", "assistant_message", None)
        }
        TurnOutcome::Finished(TurnFinish::SubmittedValue { .. }) => {
            ("completed", "submitted_value", None)
        }
        TurnOutcome::Finished(TurnFinish::ToolValue { .. }) => ("completed", "tool_value", None),
        TurnOutcome::Handoff { session_id } => (
            "completed",
            "handoff",
            Some(lash_trace::TraceHandoff {
                successor_session_id: session_id.clone(),
            }),
        ),
        TurnOutcome::Stopped(stop) => ("failed", trace_stop_reason(stop), None),
    }
}

fn trace_stop_reason(stop: &TurnStop) -> &'static str {
    match stop {
        TurnStop::Cancelled => "cancelled",
        TurnStop::Incomplete => "incomplete",
        TurnStop::InvalidInput => "invalid_input",
        TurnStop::MaxTurns => "max_turns",
        TurnStop::ToolFailure => "tool_failure",
        TurnStop::ProviderError => "provider_error",
        TurnStop::PluginAbort => "plugin_abort",
        TurnStop::RuntimeError => "runtime_error",
        TurnStop::SubmittedError { .. } => "submitted_error",
        TurnStop::ToolError { .. } => "tool_error",
    }
}

impl LashRuntime {
    fn max_context_tokens(&self) -> usize {
        self.policy
            .max_context_tokens
            .expect("lash runtime requires explicit max_context_tokens")
    }
    #[doc(hidden)]
    pub fn set_turn_phase_probe(&mut self, probe: Arc<dyn RuntimeTurnPhaseProbe>) {
        self.turn_phase_probe = Some(probe);
    }

    fn mark_phase_begin(&self, phase: RuntimeTurnPhase) {
        if let Some(probe) = self.turn_phase_probe.as_ref() {
            probe.begin(phase);
        }
    }

    fn mark_phase_end(&self, phase: RuntimeTurnPhase) {
        if let Some(probe) = self.turn_phase_probe.as_ref() {
            probe.end(phase);
        }
    }

    /// Run a single turn and stream events to the host sink.
    pub async fn stream_turn(
        &mut self,
        input: TurnInput,
        events: &dyn EventSink,
        cancel: CancellationToken,
    ) -> Result<AssembledTurn, RuntimeError> {
        self.stream_turn_with_semantic_events(input, events, &NoopTurnActivitySink, cancel)
            .await
    }

    pub(crate) async fn stream_turn_with_semantic_events(
        &mut self,
        input: TurnInput,
        events: &dyn EventSink,
        turn_events: &dyn TurnActivitySink,
        cancel: CancellationToken,
    ) -> Result<AssembledTurn, RuntimeError> {
        if let Some(execution_session_id) = self
            .active_handoff_leaf(&self.state.session_id)
            .await
            .filter(|session_id| session_id != &self.state.session_id)
        {
            return self
                .stream_turn_on_handoff_successor(
                    execution_session_id,
                    input,
                    events,
                    turn_events,
                    cancel,
                )
                .await;
        }
        self.stream_turn_inner(input.clone(), events, turn_events, cancel.clone())
            .await
    }

    async fn active_handoff_leaf(&self, session_id: &str) -> Option<String> {
        let continuations = self.active_handoff_continuations.lock().await;
        let mut current = session_id.to_string();
        let mut seen = std::collections::HashSet::new();
        while seen.insert(current.clone()) {
            let Some(next) = continuations.get(&current).cloned() else {
                return (current != session_id).then_some(current);
            };
            current = next;
        }
        None
    }

    async fn stream_turn_on_handoff_successor(
        &mut self,
        execution_session_id: String,
        input: TurnInput,
        events: &dyn EventSink,
        turn_events: &dyn TurnActivitySink,
        cancel: CancellationToken,
    ) -> Result<AssembledTurn, RuntimeError> {
        let runtime_handle = {
            let registry = self.managed_sessions.lock().await;
            registry.get(&execution_session_id).cloned()
        }
        .ok_or_else(|| RuntimeError {
            code: "handoff_successor_missing".to_string(),
            message: format!("active handoff session `{execution_session_id}` is unavailable"),
        })?;
        let mut runtime = runtime_handle.runtime.lock().await;
        runtime.state.turn_index = self.state.turn_index;
        let turn = runtime
            .stream_turn_inner(input, events, turn_events, cancel)
            .await?;
        runtime_handle.publish_from(&runtime);
        self.state.turn_index = turn.state.turn_index;
        Ok(turn)
    }

    /// Stream one logical host turn, following foreground handoffs until a
    /// non-handoff outcome is reached.
    ///
    /// RLM `continue_as` creates a successor session with queued first-turn
    /// input. Hosts that only care about the benchmark/app answer should not
    /// need to special-case that intermediate outcome; this helper activates
    /// each successor and drives its queued first turn with the normal runtime
    /// turn guards.
    pub async fn stream_turn_following_handoffs(
        &mut self,
        input: TurnInput,
        events: &dyn EventSink,
        cancel: CancellationToken,
    ) -> Result<FollowedTurn, RuntimeError> {
        self.stream_turn_following_handoffs_with_semantic_events(
            input,
            events,
            &NoopTurnActivitySink,
            cancel,
        )
        .await
    }

    pub async fn stream_turn_events_following_handoffs(
        &mut self,
        input: TurnInput,
        turn_events: &dyn TurnActivitySink,
        cancel: CancellationToken,
    ) -> Result<FollowedTurn, RuntimeError> {
        self.stream_turn_following_handoffs_with_semantic_events(
            input,
            &NoopEventSink,
            turn_events,
            cancel,
        )
        .await
    }

    pub async fn stream_turn_with_events_following_handoffs(
        &mut self,
        input: TurnInput,
        events: &dyn EventSink,
        turn_events: &dyn TurnActivitySink,
        cancel: CancellationToken,
    ) -> Result<FollowedTurn, RuntimeError> {
        self.stream_turn_following_handoffs_with_semantic_events(input, events, turn_events, cancel)
            .await
    }

    async fn stream_turn_following_handoffs_with_semantic_events(
        &mut self,
        mut input: TurnInput,
        events: &dyn EventSink,
        turn_events: &dyn TurnActivitySink,
        cancel: CancellationToken,
    ) -> Result<FollowedTurn, RuntimeError> {
        let follow_mode_turn_options = input.mode_turn_options.clone();
        let follow_turn_context = input.turn_context.clone();
        let follow_trace_turn_id = input
            .trace_turn_id
            .clone()
            .unwrap_or_else(|| uuid::Uuid::new_v4().to_string());
        input.trace_turn_id = Some(follow_trace_turn_id.clone());
        let mut turns = Vec::new();
        loop {
            let turn = self
                .stream_turn_with_semantic_events(input, events, turn_events, cancel.clone())
                .await?;
            let successor_session_id = match &turn.outcome {
                TurnOutcome::Handoff { session_id } => Some(session_id.clone()),
                _ => None,
            };
            turns.push(turn);

            let Some(successor_session_id) = successor_session_id else {
                return Ok(FollowedTurn { turns });
            };

            let seed = self
                .pending_first_turn_inputs
                .lock()
                .expect("pending first turn inputs lock")
                .remove(&successor_session_id)
                .ok_or_else(|| RuntimeError {
                    code: "handoff_missing_first_turn".to_string(),
                    message: format!(
                        "handoff session `{successor_session_id}` did not provide a first turn"
                    ),
                })?;
            input = turn_input_from_plugin_message(seed);
            input.mode_turn_options = follow_mode_turn_options.clone();
            input.trace_turn_id = Some(follow_trace_turn_id.clone());
            input.turn_context = follow_turn_context.clone();
            if let Some(successor_handle) = {
                let registry = self.managed_sessions.lock().await;
                registry.get(&successor_session_id).cloned()
            } {
                let mut successor = successor_handle.runtime.lock().await;
                successor.state.turn_index = self.state.turn_index.saturating_sub(1);
                // Keep observers aligned if a handoff successor has not
                // started its own streamed turn yet.
                successor_handle.publish_from(&successor);
            }
        }
    }

    async fn stream_turn_inner(
        &mut self,
        input: TurnInput,
        events: &dyn EventSink,
        turn_events: &dyn TurnActivitySink,
        cancel: CancellationToken,
    ) -> Result<AssembledTurn, RuntimeError> {
        self.refresh_session_graph_from_store().await;
        if let Some(extension) = &input.mode_extension
            && let Some(session) = self.session.as_ref()
        {
            let mode_session = std::sync::Arc::clone(session.plugins().mode_session());
            mode_session
                .validate_turn_extension(extension)
                .await
                .map_err(|err| RuntimeError {
                    code: "mode_turn_extension".to_string(),
                    message: err.to_string(),
                })?;
        }
        let previous_prompt_usage = self.state.last_prompt_usage.clone();
        let normalized = match self.normalize_input_items(&input.items, &input.image_blobs) {
            Ok(items) => items,
            Err(e) => {
                self.state.last_prompt_usage = None;
                let mut assembler = TurnAssembler::default();
                let error_event = SessionEvent::Error {
                    message: e.clone(),
                    envelope: Some(crate::session_model::ErrorEnvelope {
                        kind: "input_validation".to_string(),
                        code: Some("invalid_turn_input".to_string()),
                        terminal_reason: None,
                        user_message: e.clone(),
                        raw: None,
                    }),
                };
                assembler.push(&error_event);
                emit_turn_activity_to_sink(
                    turn_events,
                    TurnActivity::independent(TurnEvent::Error { message: e }),
                )
                .await;
                emit_session_event_to_sink(events, error_event).await;
                let outcome_event = SessionEvent::TurnOutcome {
                    outcome: TurnOutcome::Stopped(TurnStop::InvalidInput),
                };
                assembler.push(&outcome_event);
                emit_session_event_to_sink(events, outcome_event).await;
                assembler.push(&SessionEvent::Done);
                emit_session_event_to_sink(events, SessionEvent::Done).await;
                return Ok(assembler.finish(
                    self.state.export_state(),
                    false,
                    None,
                    &self.host.core.termination,
                ));
            }
        };
        let turn_index = self.state.turn_index + 1;
        let trace_turn_id = input
            .trace_turn_id
            .clone()
            .unwrap_or_else(|| uuid::Uuid::new_v4().to_string());
        if self.host.core.trace_sink.is_some() {
            let mut trace_metadata = std::collections::BTreeMap::new();
            trace_metadata.insert(
                "input_item_count".to_string(),
                serde_json::json!(normalized.len()),
            );
            crate::trace::emit_trace(
                &self.host.core.trace_sink,
                &self.host.core.trace_context,
                lash_trace::TraceContext::default()
                    .for_session(self.state.session_id.clone())
                    .for_turn_index(turn_index)
                    .for_turn(trace_turn_id.clone()),
                lash_trace::TraceEvent::TurnStarted {
                    metadata: trace_metadata,
                },
            );
        }

        let base_read_model = self.state.read_model();
        let base_messages = base_read_model.messages;
        let base_render_cache = base_read_model.prompt_render_cache;
        let mut turn_delta = Vec::new();

        let user_id = fresh_message_id();
        let mut user_parts: Vec<Part> = Vec::new();
        for item in normalized {
            match item {
                NormalizedItem::Text(text) => {
                    if text.is_empty() {
                        continue;
                    }
                    user_parts.push(Part {
                        id: format!("{}.p{}", user_id, user_parts.len()),
                        kind: PartKind::Text,
                        content: text,
                        attachment: None,
                        tool_call_id: None,
                        tool_name: None,
                        tool_replay: None,
                        prune_state: PruneState::Intact,
                        reasoning_meta: None,
                        response_meta: None,
                    });
                }
                NormalizedItem::Image(reference) => {
                    user_parts.push(Part {
                        id: format!("{}.p{}", user_id, user_parts.len()),
                        kind: PartKind::Image,
                        content: String::new(),
                        attachment: Some(crate::session_model::message::PartAttachment {
                            reference,
                        }),
                        tool_call_id: None,
                        tool_name: None,
                        tool_replay: None,
                        prune_state: PruneState::Intact,
                        reasoning_meta: None,
                        response_meta: None,
                    });
                }
            }
        }
        if user_parts.is_empty() {
            user_parts.push(Part {
                id: format!("{}.p0", user_id),
                kind: PartKind::Text,
                content: String::new(),
                attachment: None,
                tool_call_id: None,
                tool_name: None,
                tool_replay: None,
                prune_state: PruneState::Intact,
                reasoning_meta: None,
                response_meta: None,
            });
        }
        reassign_part_ids(&user_id, &mut user_parts);
        turn_delta.push(Message {
            id: user_id.clone(),
            role: MessageRole::User,
            parts: shared_parts(user_parts),
            origin: None,
        });

        let manager = self
            .runtime_session_manager_for_turn(None)
            .map_err(|err| RuntimeError {
                code: "plugin_session_manager".to_string(),
                message: err.to_string(),
            })?;
        let plugin_session = self
            .session
            .as_ref()
            .map(|s| Arc::clone(s.plugins()))
            .ok_or_else(|| RuntimeError {
                code: "context_prepare_turn".to_string(),
                message: "runtime session not available".to_string(),
            })?;
        let turn_ctx = crate::TurnTransformContext {
            session_id: self.state.session_id.clone(),
            state: self.read_view(),
            prompt_usage: previous_prompt_usage.clone(),
            max_context_tokens: Some(LashRuntime::max_context_tokens(self)),
            host: manager.clone(),
        };
        self.mark_phase_begin(RuntimeTurnPhase::ContextTransform);
        let prepared_context = plugin_session
            .prepare_turn_context(
                &turn_ctx,
                crate::session_model::context::PreparedContext {
                    messages: crate::MessageSequence::from_base_and_delta(
                        base_messages,
                        turn_delta,
                    )
                    .with_base_render_cache(base_render_cache),
                    ..Default::default()
                },
            )
            .await
            .map_err(|err| RuntimeError {
                code: "context_prepare_turn".to_string(),
                message: err.to_string(),
            })?;
        self.mark_phase_end(RuntimeTurnPhase::ContextTransform);
        // Release the read-view's graph clone before the rest of the turn
        // runs. Keeping it alive into `stream_prepared_turn` forces the
        // post-turn `append_active_read_delta` to deep-clone the session
        // graph (Arc::make_mut with refcount > 1).
        drop(turn_ctx);
        let messages = prepared_context.messages;
        if let Some(session) = self.session.as_mut() {
            session.set_context_surface(
                prepared_context.tool_providers,
                prepared_context.prompt_contributions,
                prepared_context.include_base_tools,
            );
        }

        self.state.last_prompt_usage = None;

        self.stream_prepared_turn(
            messages,
            previous_prompt_usage,
            input.mode_turn_options.clone(),
            input.mode_extension.clone(),
            input.turn_context.clone(),
            trace_turn_id,
            turn_index,
            events,
            turn_events,
            cancel,
        )
        .await
    }

    /// Run a single turn and return only the assembled terminal result.
    pub async fn run_turn_assembled(
        &mut self,
        input: TurnInput,
        cancel: CancellationToken,
    ) -> Result<AssembledTurn, RuntimeError> {
        self.stream_turn(input, &NoopEventSink, cancel).await
    }

    /// Run a turn using host-prepared message history.
    #[allow(clippy::too_many_arguments)]
    pub async fn stream_prepared_turn(
        &mut self,
        messages: crate::MessageSequence,
        _previous_prompt_usage: Option<PromptUsage>,
        mode_turn_options: Option<crate::ModeTurnOptions>,
        mode_extension: Option<crate::ModeTurnExtensionHandle>,
        turn_context: crate::TurnContext,
        trace_turn_id: String,
        turn_index: usize,
        events: &dyn EventSink,
        turn_events: &dyn TurnActivitySink,
        cancel: CancellationToken,
    ) -> Result<AssembledTurn, RuntimeError> {
        let (event_tx, mut event_rx) = mpsc::channel::<RuntimeStreamEvent>(100);
        let child_usage_event_relay = ChildUsageEventRelay::new(event_tx.clone());
        let mut turn_policy = self.policy.clone();
        if let Some(provider) = turn_context.provider().cloned() {
            let model = provider.default_model().to_string();
            let model_variant = provider.default_model_variant(&model).map(str::to_string);
            turn_policy.provider = provider;
            turn_policy.model = model;
            turn_policy.model_variant = model_variant;
        }
        if let Some((model, variant)) = turn_context.model_selection() {
            turn_policy.model = model.to_string();
            turn_policy.model_variant = variant.map(str::to_string);
        }
        let effective_mode_turn_options = mode_turn_options
            .clone()
            .unwrap_or_else(|| self.mode_turn_options.clone());
        let manager = self
            .runtime_session_manager_for_turn(Some(child_usage_event_relay.clone()))
            .map_err(|err| RuntimeError {
                code: "plugin_session_manager".to_string(),
                message: err.to_string(),
            })?;
        let plugins = {
            let session = self
                .session
                .as_ref()
                .expect("lash runtime session must be available");
            Arc::clone(session.plugins())
        };
        let capture_text_deltas =
            turn_policy.provider.requires_streaming() || plugins.has_assistant_stream_hooks();
        let mut assembler = TurnAssembler::new(capture_text_deltas);
        self.mark_phase_begin(RuntimeTurnPhase::BeforeTurnHooks);
        // Block-scope the pinned future so it (and its captured
        // `SessionReadView` clone of the session graph) drops before the
        // post-turn `append_active_read_delta` mutation. Keeping it alive
        // across the turn forces `Arc::make_mut` to deep-clone
        // `SessionGraphData`.
        let prepared = {
            let prepare_turn = plugins.prepare_turn(PrepareTurnRequest {
                session_id: self.state.session_id.clone(),
                state: crate::SessionReadView::from_runtime_state(
                    &self.state,
                    turn_policy.clone(),
                    effective_mode_turn_options.clone(),
                ),
                messages,
                host: manager.clone(),
                turn_context: turn_context.clone(),
            });
            tokio::pin!(prepare_turn);

            loop {
                tokio::select! {
                    prepared = &mut prepare_turn => {
                        let prepared = prepared.map_err(|err| RuntimeError {
                            code: "plugin_prepare_turn".to_string(),
                            message: err.to_string(),
                        })?;
                        self.mark_phase_end(RuntimeTurnPhase::BeforeTurnHooks);
                        break prepared;
                    }
                    maybe_event = event_rx.recv() => {
                        if let Some(event) = maybe_event {
                            emit_runtime_stream_event_to_sinks(
                                events,
                                turn_events,
                                event,
                                &mut assembler,
                            )
                            .await;
                        }
                    }
                }
            }
        };
        for event in &prepared.events {
            assembler.push(event);
        }
        emit_session_events_to_sink(events, prepared.events).await;
        if let Some(abort) = prepared.abort {
            drop(event_tx);

            let mut turn_pipeline = TurnCommitPipeline::from_state(self.state.clone());
            turn_pipeline.apply_prepared_messages(&prepared.messages);
            let state = turn_pipeline.into_final_state();
            let issue = TurnIssue {
                kind: "plugin".to_string(),
                code: Some(abort.code),
                terminal_reason: None,
                message: abort.message.clone(),
                raw: None,
            };
            let error_event = SessionEvent::Error {
                message: abort.message,
                envelope: Some(crate::session_model::ErrorEnvelope {
                    kind: "plugin".to_string(),
                    code: issue.code.clone(),
                    terminal_reason: None,
                    user_message: issue.message.clone(),
                    raw: None,
                }),
            };
            assembler.push(&error_event);
            emit_turn_activity_to_sink(
                turn_events,
                TurnActivity::independent(TurnEvent::Error {
                    message: issue.message.clone(),
                }),
            )
            .await;
            emit_session_event_to_sink(events, error_event).await;
            let outcome_event = SessionEvent::TurnOutcome {
                outcome: TurnOutcome::Stopped(TurnStop::PluginAbort),
            };
            assembler.push(&outcome_event);
            emit_session_event_to_sink(events, outcome_event).await;
            assembler.push(&SessionEvent::Done);
            emit_session_event_to_sink(events, SessionEvent::Done).await;
            return Ok(assembler.finish(
                state.export_state(),
                cancel.is_cancelled(),
                Some(issue),
                &self.host.core.termination,
            ));
        }
        let mut turn_pipeline = TurnCommitPipeline::from_state(self.state.clone());
        let store = self
            .session
            .as_ref()
            .and_then(|session| session.history_store());
        turn_pipeline
            .prepared_checkpoint(
                store.as_ref().map(|store| store.as_ref()),
                turn_policy.clone(),
                turn_index,
                &prepared.messages,
                self.session.as_mut(),
            )
            .await
            .map_err(|err| RuntimeError {
                code: "store_commit_failed".to_string(),
                message: err.to_string(),
            })?;
        let cancel_state = cancel.clone();
        let session = self
            .session
            .take()
            .expect("lash runtime session must be available");
        let mut driver = RuntimeTurnDriver {
            session,
            policy: turn_policy.clone(),
            host: self.host.clone(),
            session_id: self.state.session_id.clone(),
            turn_id: trace_turn_id.clone(),
            turn_index,
            turn_pipeline,
            llm_stream_summaries: HashMap::new(),
            next_llm_ordinal: 0,
            session_manager: manager,
            mode_turn_options: effective_mode_turn_options,
            mode_extension,
            turn_context,
            turn_phase_probe: self.turn_phase_probe.clone(),
        };
        let mode_run_offset = 0;
        let run_task = tokio::spawn(async move {
            let (new_messages, new_mode_iteration) = driver
                .run(prepared.messages, event_tx, cancel, mode_run_offset)
                .await;
            (driver, new_messages, new_mode_iteration)
        });
        tokio::pin!(run_task);

        self.mark_phase_begin(RuntimeTurnPhase::EffectLoop);
        let (driver, new_messages, _new_mode_iteration) = loop {
            tokio::select! {
                maybe_event = event_rx.recv() => {
                    if let Some(event) = maybe_event {
                        emit_runtime_stream_event_to_sinks(
                            events,
                            turn_events,
                            event,
                            &mut assembler,
                        )
                        .await;
                    }
                }
                joined = &mut run_task => {
                    child_usage_event_relay.clear();
                    let joined = match joined {
                        Ok(v) => v,
                        Err(e) => {
                            let issue = TurnIssue {
                                kind: "runtime".to_string(),
                                code: Some("run_task_join_failed".to_string()),
                                terminal_reason: None,
                                message: format!("Runtime turn task failed: {e}"),
                                raw: None,
                            };
                            return Ok(assembler.finish(
                                self.state.export_state(),
                                cancel_state.is_cancelled(),
                                Some(issue),
                                &self.host.core.termination,
                            ));
                        }
                    };
                    break joined;
                }
            }
        };
        while let Some(event) = event_rx.recv().await {
            emit_runtime_stream_event_to_sinks(events, turn_events, event, &mut assembler).await;
        }
        self.mark_phase_end(RuntimeTurnPhase::EffectLoop);
        tracing::debug!(
            rss_kb = debug_rss_kb(),
            new_message_count = new_messages.len(),
            tool_call_count = assembler.tool_calls.len(),
            "runtime post-run_task"
        );

        // Drain the shared token ledger (child sessions + direct
        // completions + async OM observers/reflectors). Merge it after
        // restoring the latest progress checkpoint state so in-turn
        // progress commits cannot wipe live child usage.
        let child_ledger = {
            let mut ledger = self.shared_token_ledger.lock().expect("token ledger lock");
            std::mem::take(&mut *ledger)
        };

        let RuntimeTurnDriver {
            session,
            policy,
            mut turn_pipeline,
            ..
        } = driver;
        self.session = Some(session);
        self.policy = self.state.policy.clone();
        turn_pipeline.state_mut().policy = self.policy.clone();
        turn_pipeline.state_mut().turn_index = turn_index;
        let mut turn_usage_delta = child_ledger.clone();
        if assembler.token_usage.total() > 0 || assembler.token_usage.cached_input_tokens > 0 {
            let entry = TokenLedgerEntry {
                source: "turn".to_string(),
                model: self.policy.model.clone(),
                usage: assembler.token_usage.clone(),
            };
            turn_usage_delta.push(entry);
        }
        let turn_usage_delta = merge_usage_delta_entries(turn_usage_delta);
        turn_pipeline.finalize_turn_read_state(
            new_messages,
            &assembler.tool_calls,
            cancel_state.is_cancelled(),
        );
        if assembler.token_usage.total() > 0 || assembler.token_usage.cached_input_tokens > 0 {
            turn_pipeline.state_mut().token_usage = assembler.token_usage.clone();
        }

        let last_prompt_usage = assembler
            .last_llm_usage()
            .and_then(|usage| normalize_prompt_usage(&policy.provider, usage));
        let finalize_manager = if self.session.is_some() {
            Some(
                self.runtime_session_manager_for_turn(None)
                    .map_err(|err| RuntimeError {
                        code: "plugin_session_manager".to_string(),
                        message: err.to_string(),
                    })?,
            )
        } else {
            None
        };
        tracing::debug!(
            rss_kb = debug_rss_kb(),
            state_message_count = turn_pipeline.state_mut().read_model().messages.len(),
            graph_node_count = turn_pipeline.state_mut().session_graph.nodes.len(),
            token_ledger_entries = turn_pipeline.state_mut().token_ledger.len(),
            "runtime before assembler.finish"
        );
        turn_pipeline.state_mut().last_prompt_usage = last_prompt_usage.clone();
        let assembled_state = turn_pipeline.export_state_for_assembly();
        let assembled = assembler.finish(
            assembled_state,
            cancel_state.is_cancelled(),
            None,
            &self.host.core.termination,
        );
        tracing::debug!(
            rss_kb = debug_rss_kb(),
            assembled_message_count = assembled.state.read_model().messages.len(),
            assembled_graph_node_count = assembled.state.session_graph.nodes.len(),
            "runtime after assembler.finish"
        );
        if let Some(session) = self.session.as_ref() {
            let plugins = Arc::clone(session.plugins());
            let manager = finalize_manager.expect("finalize manager should exist with session");
            tracing::debug!(rss_kb = debug_rss_kb(), "runtime before finalize_turn");
            self.mark_phase_begin(RuntimeTurnPhase::FinalizeTurn);
            let finalized = plugins
                .finalize_turn(assembled, manager)
                .await
                .map_err(|err| RuntimeError {
                    code: "plugin_finalize_turn".to_string(),
                    message: err.to_string(),
                })?;
            self.mark_phase_end(RuntimeTurnPhase::FinalizeTurn);
            tracing::debug!(
                rss_kb = debug_rss_kb(),
                finalized_message_count = finalized.turn.state.read_model().messages.len(),
                "runtime after finalize_turn"
            );
            let mut returned_turn = finalized.turn;
            tracing::debug!(
                rss_kb = debug_rss_kb(),
                tool_state_present = turn_pipeline.state_mut().tool_state_ref.is_some()
                    || turn_pipeline.state_mut().tool_state_snapshot.is_some(),
                plugin_snapshot_present = turn_pipeline.state_mut().plugin_snapshot_ref.is_some()
                    || turn_pipeline.state_mut().plugin_snapshot.is_some(),
                "runtime before stamp_runtime_state"
            );
            self.mark_phase_begin(RuntimeTurnPhase::PersistTurn);
            turn_pipeline
                .final_commit(&mut returned_turn, self.session.as_mut(), &turn_usage_delta)
                .await?;
            tracing::debug!(
                rss_kb = debug_rss_kb(),
                resident_graph_node_count = returned_turn.state.session_graph.nodes.len(),
                persisted_message_count = returned_turn.state.read_model().messages.len(),
                "runtime after stamp_runtime_state"
            );
            emit_session_events_to_sink(events, finalized.events).await;
            self.state = turn_pipeline.into_final_state();
            if let Some(session) = self.session.as_ref()
                && let Ok(host) = self.runtime_session_manager()
            {
                session
                    .plugins()
                    .emit_runtime_event(crate::PluginRuntimeEvent::TurnPersisted(
                        crate::SessionStateChangedContext {
                            session_id: self.state.session_id.clone(),
                            state: crate::SessionReadView::from_exported_state(
                                &returned_turn.state,
                            ),
                            host,
                        },
                    ))
                    .await;
            }
            self.mark_phase_end(RuntimeTurnPhase::PersistTurn);
            if self.host.core.trace_sink.is_some() {
                let (status, done_reason, handoff) =
                    trace_fields_from_outcome(&returned_turn.outcome);
                crate::trace::emit_trace(
                    &self.host.core.trace_sink,
                    &self.host.core.trace_context,
                    lash_trace::TraceContext::default()
                        .for_session(returned_turn.state.session_id.clone())
                        .for_turn_index(returned_turn.state.turn_index)
                        .for_turn(trace_turn_id.clone()),
                    lash_trace::TraceEvent::TurnCompleted {
                        status: status.to_string(),
                        done_reason: done_reason.to_string(),
                        handoff,
                    },
                );
            }
            Ok(returned_turn)
        } else {
            self.state.apply_exported_state(&assembled.state);
            if self.host.core.trace_sink.is_some() {
                let (status, done_reason, handoff) = trace_fields_from_outcome(&assembled.outcome);
                crate::trace::emit_trace(
                    &self.host.core.trace_sink,
                    &self.host.core.trace_context,
                    lash_trace::TraceContext::default()
                        .for_session(assembled.state.session_id.clone())
                        .for_turn_index(assembled.state.turn_index)
                        .for_turn(trace_turn_id),
                    lash_trace::TraceEvent::TurnCompleted {
                        status: status.to_string(),
                        done_reason: done_reason.to_string(),
                        handoff,
                    },
                );
            }
            Ok(assembled)
        }
    }
    fn normalize_input_items(
        &self,
        items: &[InputItem],
        image_blobs: &HashMap<String, Vec<u8>>,
    ) -> Result<Vec<NormalizedItem>, String> {
        normalize_input_items(items, image_blobs, self.host.core.attachment_store.as_ref())
    }
}

fn turn_input_from_plugin_message(message: PluginMessage) -> TurnInput {
    let mut items = Vec::new();
    if !message.content.is_empty() {
        items.push(InputItem::Text {
            text: message.content,
        });
    }
    let mut image_blobs = HashMap::new();
    for (index, bytes) in message.images.into_iter().enumerate() {
        let id = format!("handoff-seed-image-{index}");
        image_blobs.insert(id.clone(), bytes);
        items.push(InputItem::ImageRef { id });
    }
    TurnInput {
        items,
        image_blobs,
        mode_turn_options: None,
        trace_turn_id: None,
        mode_extension: None,
        turn_context: crate::TurnContext::default(),
    }
}

async fn emit_turn_activity_to_sink(events: &dyn TurnActivitySink, activity: TurnActivity) {
    if !events.is_noop() {
        events.emit(activity).await;
    }
}

async fn emit_runtime_stream_event_to_sinks(
    events: &dyn EventSink,
    turn_events: &dyn TurnActivitySink,
    event: RuntimeStreamEvent,
    assembler: &mut TurnAssembler,
) {
    match event {
        RuntimeStreamEvent::Session(event) => {
            assembler.push(&event);
            emit_session_event_to_sink(events, event).await;
        }
        RuntimeStreamEvent::Turn(activity) => {
            assembler.push_turn_activity(&activity);
            emit_turn_activity_to_sink(turn_events, activity).await;
        }
    }
}