merged with fixes

internal/rpcresult/replay.go

@@ -0,0 +1,72 @@
+package rpcresult
+
+import (
+	"context"
+	"sync"
+
+	"github.com/iamxvbaba/td/bin"
+)
+
+// ReplaySource rebuilds the exact inner result bytes for one already-executed
+// RPC from immutable data. Implementations must not rerun authorization,
+// metadata lookup, or business handlers.
+type ReplaySource interface {
+	EncodeInner(context.Context, *bin.Buffer) error
+	RetainedBytes() int
+}
+
+// Carrier is implemented by a generated result wrapper when a fresh execution
+// proved that its result can be replayed from immutable data.
+type Carrier interface {
+	ExactReplaySource() ReplaySource
+}
+
+// ValueSource is the RPC-side half of a replay source. It may use canonical
+// RPC values internally; the edge sees only the encoded ReplaySource above.
+type ValueSource interface {
+	Value(context.Context) (any, error)
+	RetainedBytes() int
+}
+
+type captureKey struct{}
+
+type Capture struct {
+	mu     sync.Mutex
+	source ValueSource
+}
+
+func WithCapture(ctx context.Context) (context.Context, *Capture) {
+	capture := &Capture{}
+	return context.WithValue(ctx, captureKey{}, capture), capture
+}
+
+// Publish records the one immutable source produced by the admitted terminal.
+// Wrapper or nested handlers must not replace a source already published by
+// the same one-shot dispatch.
+func Publish(ctx context.Context, source ValueSource) bool {
+	if source == nil {
+		return false
+	}
+	capture, _ := ctx.Value(captureKey{}).(*Capture)
+	if capture == nil {
+		return false
+	}
+	capture.mu.Lock()
+	defer capture.mu.Unlock()
+	if capture.source != nil {
+		return false
+	}
+	capture.source = source
+	return true
+}
+
+func (c *Capture) Take() ValueSource {
+	if c == nil {
+		return nil
+	}
+	c.mu.Lock()
+	source := c.source
+	c.source = nil
+	c.mu.Unlock()
+	return source
+}