feat(executor): introduce AgentChannel seam for runner signals

Defines AgentChannel — the normalized interface by which a runner reports
agent-originated signals (AskUser, ReportSummary, SpawnSubtask,
RecordProgress) — plus a default storeChannel implementation backed by
storage. Runner.Run now takes an AgentChannel; the pool constructs one
per execution.

The file transport routes its post-exit summary detection through
ch.ReportSummary (buffered onto the execution so the pool still applies
its extract/synthesize fallbacks, no double-write). AskUser returns
ErrAgentBlocked since write-and-exit cannot answer in-session; question
persistence stays with the pool's BlockedError handling. SpawnSubtask
and RecordProgress are implemented and tested, ready for the MCP
transport in Phase 2 where the channel becomes fully load-bearing.

Store gains CreateEvent so the channel can emit agent_message events.

https://claude.ai/code/session_01SESwn7kQ7oP62trWw6pc39

1 files changed, 118 insertions, 0 deletions

diff --git a/internal/executor/channel_test.go b/internal/executor/channel_test.go
new file mode 100644
index 0000000..822dd35
--- /dev/null
+++ b/internal/executor/channel_test.go
@@ -0,0 +1,118 @@
+package executor
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/thepeterstone/claudomator/internal/event"
+	"github.com/thepeterstone/claudomator/internal/storage"
+	"github.com/thepeterstone/claudomator/internal/task"
+)
+
+type fakeChannelStore struct {
+	createdTasks  []*task.Task
+	createdEvents []*event.Event
+	createTaskErr error
+}
+
+func (f *fakeChannelStore) CreateTask(t *task.Task) error {
+	if f.createTaskErr != nil {
+		return f.createTaskErr
+	}
+	f.createdTasks = append(f.createdTasks, t)
+	return nil
+}
+
+func (f *fakeChannelStore) CreateEvent(e *event.Event) error {
+	f.createdEvents = append(f.createdEvents, e)
+	return nil
+}
+
+func TestStoreChannel_AskUser_ReturnsBlocked(t *testing.T) {
+	ch := newStoreChannel(&fakeChannelStore{}, "task-1", &storage.Execution{})
+	answer, err := ch.AskUser(context.Background(), `{"text":"q"}`)
+	if !errors.Is(err, ErrAgentBlocked) {
+		t.Errorf("expected ErrAgentBlocked, got %v", err)
+	}
+	if answer != "" {
+		t.Errorf("expected empty answer, got %q", answer)
+	}
+}
+
+func TestStoreChannel_ReportSummary_BuffersOntoExec(t *testing.T) {
+	e := &storage.Execution{}
+	ch := newStoreChannel(&fakeChannelStore{}, "task-1", e)
+	if err := ch.ReportSummary(context.Background(), "did the thing"); err != nil {
+		t.Fatalf("ReportSummary: %v", err)
+	}
+	if e.Summary != "did the thing" {
+		t.Errorf("expected exec.Summary set, got %q", e.Summary)
+	}
+}
+
+func TestStoreChannel_ReportSummary_NilExec(t *testing.T) {
+	ch := newStoreChannel(&fakeChannelStore{}, "task-1", nil)
+	if err := ch.ReportSummary(context.Background(), "x"); err != nil {
+		t.Errorf("expected nil err with nil exec, got %v", err)
+	}
+}
+
+func TestStoreChannel_SpawnSubtask_CreatesChildWithParent(t *testing.T) {
+	store := &fakeChannelStore{}
+	ch := newStoreChannel(store, "parent-1", &storage.Execution{})
+	id, err := ch.SpawnSubtask(context.Background(), SubtaskSpec{
+		Name:         "child",
+		Instructions: "do it",
+		Model:        "sonnet",
+		MaxBudgetUSD: 1.5,
+	})
+	if err != nil {
+		t.Fatalf("SpawnSubtask: %v", err)
+	}
+	if id == "" {
+		t.Error("expected non-empty subtask ID")
+	}
+	if len(store.createdTasks) != 1 {
+		t.Fatalf("expected 1 created task, got %d", len(store.createdTasks))
+	}
+	ct := store.createdTasks[0]
+	if ct.ParentTaskID != "parent-1" {
+		t.Errorf("ParentTaskID: got %q want parent-1", ct.ParentTaskID)
+	}
+	if ct.ID != id {
+		t.Errorf("returned id %q != created task id %q", id, ct.ID)
+	}
+	if ct.Agent.Instructions != "do it" || ct.Agent.Model != "sonnet" || ct.Agent.MaxBudgetUSD != 1.5 {
+		t.Errorf("agent config not propagated: %+v", ct.Agent)
+	}
+	if ct.State != task.StatePending {
+		t.Errorf("expected PENDING child, got %s", ct.State)
+	}
+}
+
+func TestStoreChannel_SpawnSubtask_PropagatesError(t *testing.T) {
+	store := &fakeChannelStore{createTaskErr: errors.New("boom")}
+	ch := newStoreChannel(store, "parent-1", &storage.Execution{})
+	if _, err := ch.SpawnSubtask(context.Background(), SubtaskSpec{Name: "x"}); err == nil {
+		t.Error("expected error from CreateTask")
+	}
+}
+
+func TestStoreChannel_RecordProgress_EmitsAgentMessage(t *testing.T) {
+	store := &fakeChannelStore{}
+	ch := newStoreChannel(store, "task-1", &storage.Execution{})
+	if err := ch.RecordProgress(context.Background(), "halfway done"); err != nil {
+		t.Fatalf("RecordProgress: %v", err)
+	}
+	if len(store.createdEvents) != 1 {
+		t.Fatalf("expected 1 event, got %d", len(store.createdEvents))
+	}
+	e := store.createdEvents[0]
+	if e.Kind != event.KindAgentMessage || e.Actor != event.ActorAgent {
+		t.Errorf("got kind=%v actor=%v want agent_message/agent", e.Kind, e.Actor)
+	}
+	if e.TaskID != "task-1" {
+		t.Errorf("TaskID: got %q want task-1", e.TaskID)
+	}
+}