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, 7 insertions, 7 deletions

diff --git a/internal/executor/gemini_test.go b/internal/executor/gemini_test.go
index cd11ebc..c8f7422 100644
--- a/internal/executor/gemini_test.go
+++ b/internal/executor/gemini_test.go
@@ -125,7 +125,7 @@ func TestGeminiRunner_Run_InaccessibleProjectDir_ReturnsError(t *testing.T) {
 	}
 	exec := &storage.Execution{ID: "test-exec"}
 
-	err := r.Run(context.Background(), tk, exec)
+	err := r.Run(context.Background(), tk, exec, newStoreChannel(nil, tk.ID, exec))
 
 	if err == nil {
 		t.Fatal("expected error for inaccessible project_dir, got nil")
@@ -213,7 +213,7 @@ func TestGeminiRunner_Run_ProjectDir_RunsInSandbox(t *testing.T) {
 	}
 	e := &storage.Execution{ID: "sandbox-exec", TaskID: "task-1"}
 
-	if err := r.Run(context.Background(), tk, e); err != nil {
+	if err := r.Run(context.Background(), tk, e, newStoreChannel(nil, tk.ID, e)); err != nil {
 		t.Fatalf("Run: %v", err)
 	}
 
@@ -261,7 +261,7 @@ fi
 	}
 	e := &storage.Execution{ID: "blocked-gemini-exec", TaskID: "task-1"}
 
-	err := r.Run(context.Background(), tk, e)
+	err := r.Run(context.Background(), tk, e, newStoreChannel(nil, tk.ID, e))
 
 	var blocked *BlockedError
 	if !errors.As(err, &blocked) {
@@ -301,7 +301,7 @@ func TestGeminiRunner_Run_ExecError_PreservesSandbox(t *testing.T) {
 	}
 	e := &storage.Execution{ID: "err-gemini-exec", TaskID: "task-1"}
 
-	err := r.Run(context.Background(), tk, e)
+	err := r.Run(context.Background(), tk, e, newStoreChannel(nil, tk.ID, e))
 	if err == nil {
 		t.Fatal("expected error from failing gemini exit")
 	}
@@ -352,7 +352,7 @@ func TestGeminiRunner_Run_ResumeUsesStoredSandboxDir(t *testing.T) {
 		SandboxDir:      sandboxDir,
 	}
 
-	if err := r.Run(context.Background(), tk, e); err != nil {
+	if err := r.Run(context.Background(), tk, e, newStoreChannel(nil, tk.ID, e)); err != nil {
 		t.Fatalf("Run with preserved sandbox: %v", err)
 	}
 
@@ -400,7 +400,7 @@ func TestGeminiRunner_Run_StaleSandboxDir_ClonesAfresh(t *testing.T) {
 		SandboxDir:      staleSandbox,
 	}
 
-	if err := r.Run(context.Background(), tk, e); err != nil {
+	if err := r.Run(context.Background(), tk, e, newStoreChannel(nil, tk.ID, e)); err != nil {
 		t.Fatalf("Run with stale sandbox: %v", err)
 	}
 
@@ -438,7 +438,7 @@ func TestGeminiRunner_Run_NoProjectDir_SkipsSandbox(t *testing.T) {
 	}
 	e := &storage.Execution{ID: "no-pd-gemini", TaskID: "task-nopd"}
 
-	if err := r.Run(context.Background(), tk, e); err != nil {
+	if err := r.Run(context.Background(), tk, e, newStoreChannel(nil, tk.ID, e)); err != nil {
 		t.Fatalf("Run without project_dir: %v", err)
 	}
 	if e.SandboxDir != "" {