fix(sdk): allow Compensate from InFlight for known failures

Compensate previously only accepted Unresolved state, but agents that
observe an action fail during InFlight (e.g., HTTP error, payment
rejected) need to mark the intent as terminal immediately. Without
this, failed intents remain InFlight, Compensate silently fails, and
Prune cannot remove them — leading to stale non-terminal intents
accumulating in effect state.

Widen Compensate to accept both InFlight and Unresolved:
- InFlight → Compensated: agent observed the failure directly
- Unresolved → Compensated: agent investigated after crash

Fixes the deployer and x402buyer error paths which already called
Compensate after Begin but got silent errInvalidTransition errors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: simonovic86

sdk/igor/effects.go

@@ -94,14 +94,16 @@ func (e *EffectLog) Confirm(id []byte) error {
 	return nil
 }
 
-// Compensate transitions an intent from Unresolved to Compensated.
+// Compensate transitions an intent from InFlight or Unresolved to Compensated.
 // Call this after determining the action did not happen or was rolled back.
+// From InFlight: the agent observed the action fail (e.g., HTTP error, payment rejected).
+// From Unresolved: the agent investigated after a crash and determined the action didn't complete.
 func (e *EffectLog) Compensate(id []byte) error {
 	intent := e.find(id)
 	if intent == nil {
 		return errIntentNotFound
 	}
-	if intent.State != Unresolved {
+	if intent.State != InFlight && intent.State != Unresolved {
 		return errInvalidTransition
 	}
 	intent.State = Compensated

sdk/igor/effects_test.go

@@ -78,10 +78,6 @@ func TestEffectLog_InvalidTransitions(t *testing.T) {
 	if err := e.Begin(id); err == nil {
 		t.Fatal("expected error: Begin from InFlight")
 	}
-	// Can't Compensate from InFlight (only from Unresolved).
-	if err := e.Compensate(id); err == nil {
-		t.Fatal("expected error: Compensate from InFlight")
-	}
 
 	e.Confirm(id)
 
@@ -164,6 +160,28 @@ func TestEffectLog_Compensate(t *testing.T) {
 	}
 }
 
+func TestEffectLog_CompensateFromInFlight(t *testing.T) {
+	var e EffectLog
+	id := []byte("tx")
+	e.Record(id, nil)
+	e.Begin(id)
+
+	// Agent observes the action fail (e.g., HTTP error, payment rejected).
+	// It knows the action didn't complete, so it compensates directly.
+	if err := e.Compensate(id); err != nil {
+		t.Fatalf("Compensate from InFlight: %v", err)
+	}
+	if e.Get(id).State != Compensated {
+		t.Fatal("expected Compensated")
+	}
+
+	// Compensated is terminal — prune should remove it.
+	removed := e.Prune()
+	if removed != 1 {
+		t.Fatalf("expected 1 pruned, got %d", removed)
+	}
+}
+
 func TestEffectLog_ConfirmFromUnresolved(t *testing.T) {
 	var e EffectLog
 	id := []byte("tx")