fix(02-03): expand expected placeholders after replay capture

Unquoted numeric id placeholders made recorded JSON illegal to parse.
Replay now recaptures, persists vars, expands the expected body, and
diffs against the live response.

Co-authored-by: Cursor <cursoragent@cursor.com>

tide/replay.go

@@ -59,7 +59,18 @@ func ReplayFlow(ctx context.Context, flow Flow, cfg ReplayConfig) (Result, error
 			skipRest = true
 			continue
 		}
-		_ = ScrubStep(store, &live)
+		if err := store.Save(); err != nil {
+			return result, fmt.Errorf("tide: replay step %s: %w", step.ID, err)
+		}
+		want.Response, err = expandResponse(want.Response, store)
+		if err != nil {
+			sr.OK = false
+			result.OK = false
+			sr.Diffs = append(sr.Diffs, Diff{Path: "expected", Expected: "resolved placeholders", Actual: err.Error()})
+			result.Steps = append(result.Steps, sr)
+			skipRest = true
+			continue
+		}
 		sr.Diffs = append(sr.Diffs, compareStep(want, live.Response)...)
 		if len(sr.Diffs) > 0 {
 			sr.OK = false