test: align paired browser settle timing

crates/obscura-browser/src/page.rs

@@ -1242,11 +1242,24 @@ impl Page {
         }
         let hydration_snapshot = self.js.as_ref().and_then(capture_hydration_snapshot);
         if let Some(js) = &mut self.js {
-            // Bounded against both async idle and synchronous microtask storms:
-            // a plain tokio timeout cannot preempt a page that pins the thread
-            // inside V8 (the real-world SPA hang), so settle drives the loop
-            // through the watchdog-guarded path.
+            if std::env::var_os("OBSCURA_STRICT_SETTLE").is_some() {
+                // Paired browser measurements need the same wall-clock interval
+                // after load in both engines. The ordinary product path returns
+                // as soon as the loop is idle for speed; strict mode pumps all
+                // pending work, then retains the remaining wall-clock delay.
+                let started = tokio::time::Instant::now();
                 let _ = js.run_event_loop_bounded(max_ms).await;
+                let requested = tokio::time::Duration::from_millis(max_ms);
+                let elapsed = started.elapsed();
+                if elapsed < requested {
+                    tokio::time::sleep(requested - elapsed).await;
+                }
+            } else {
+                // Bounded against both async idle and synchronous microtask
+                // storms: a plain tokio timeout cannot preempt a page that pins
+                // the thread inside V8, so settle uses the watchdog path.
+                let _ = js.run_event_loop_bounded(max_ms).await;
+            }
 
             if let Some(before) = hydration_snapshot {
                 let _ = restore_hydration_snapshot_if_needed(js, before);

crates/obscura-cli/src/main.rs

@@ -970,7 +970,18 @@ async fn wait_for_selector(page: &mut Page, selector: &str, timeout_secs: u64) -
             return false;
         }
 
-        tokio::time::sleep(tokio::time::Duration::from_millis(100)).await;
+        // The selector may be created by a timer, dynamic import, or fetch
+        // completion. Sleeping without pumping V8 makes those callbacks unable
+        // to run, so a valid selector wait always times out. Drive one bounded
+        // event-loop slice, then retain a 100ms polling cadence if it returned
+        // idle immediately.
+        let slice_started = tokio::time::Instant::now();
+        page.settle(100).await;
+        let spent = slice_started.elapsed();
+        let cadence = tokio::time::Duration::from_millis(100);
+        if spent < cadence {
+            tokio::time::sleep(cadence - spent).await;
+        }
     }
 }
 

render-repros/paired-corpus.py

@@ -54,6 +54,13 @@ def capture_obscura(binary, url, screenshot, log, width, height, settle_ms):
         OBSCURA_SHOT_W=str(width),
         OBSCURA_SHOT_H=str(height),
         OBSCURA_ALLOW_PRIVATE_NETWORK="1",
+        # Product fetches return early when the event loop becomes idle. Paired
+        # captures instead need the same complete post-load wall interval that
+        # Playwright's wait_for_timeout below uses.
+        OBSCURA_STRICT_SETTLE="1",
+        # Match Playwright's 50-second goto allowance. This is the browser
+        # engine's millisecond ceiling, distinct from the CLI's seconds unit.
+        OBSCURA_NAV_TIMEOUT_MS="50000",
     )
     command = [
         binary,
@@ -62,7 +69,7 @@ def capture_obscura(binary, url, screenshot, log, width, height, settle_ms):
         "--screenshot",
         str(screenshot),
         "--timeout",
-        "50000",
+        "50",
         "--wait",
         f"{settle_ms / 1000:g}",
     ]
@@ -119,6 +126,8 @@ def main():
         "started_utc": datetime.now(timezone.utc).isoformat(),
         "viewport": {"width": args.width, "height": args.height, "dpr": 1},
         "settle_ms_after_load": args.settle_ms,
+        "settle_semantics": "full wall-clock interval while pumping each engine",
+        "navigation_timeout_ms": 50000,
         "obscura": binary_version(args.obscura_bin),
         "baseline": binary_version(args.baseline_bin) if args.baseline_bin else None,
         "pages": [],