The page stops recursing when a tap ends long after its answer (#378)

endTap reported the tap before clearing it; report's traceparent starts a
new trace when the last is over a minute old, and newTrace ends the open tap
again, so hiding the page (switching apps on the phone) a minute after using
it recursed until the stack ran out. Timings are never throttled, so nothing
broke the loop. Introduced in #376.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/page-unit.js

@@ -242,3 +242,10 @@ test('a tap is its trace\'s root span, reported with its ids once it has an answ
   assert.equal(run(`sent.at(-1)[0]`), '/api/client');
   assert.deepEqual([body.ev, body.ms, body.msg, body.span.length, body.trace.length], ['tap', 250, 'keydown', 16, 32]);
 });
+
+test('a tap ended over a minute after its last request reports once, without recursing (#378)', () => {
+  run(`globalThis.sent = []; fetch = (url, o) => { sent.push([url, o]); return Promise.resolve({ ok: true, status: 204 }); }`);
+  run(`newTrace('pointerdown'); answeredAt = rootAt + 100; traceAt = Date.now() - 120_000`);
+  run('endTap()');
+  assert.equal(run(`sent.filter(([u, o]) => JSON.parse(o.body).ev === 'tap').length`), 1);
+});

web/CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Fixed
+- Switching away from the page a minute after using it no longer stops it with "Maximum call stack size exceeded" (#378).
 
 - Two items from different feeds that share an id, as a blog's RSS and Atom feeds' do, are told apart: in All Subscriptions the second can be opened and marked read, where the first was marked whichever was clicked (#361).
 

web/src/util.ts

@@ -109,9 +109,12 @@ function spanText(secs: number){
 let traceId='', traceAt=0, rootId='', rootAt=0, rootKind='', answeredAt=0;
 const hex=(n: number)=>Array.from(crypto.getRandomValues(new Uint8Array(n)),b=>b.toString(16).padStart(2,'0')).join('');
 function endTap(){
-  if(rootKind && answeredAt>rootAt)
+  const kind=rootKind;
-    report('tap',{trace:traceId,span:rootId,start:rootAt,ms:Math.min(answeredAt-rootAt,60_000),msg:rootKind});
+  // Cleared first: report's traceparent can start a new trace, whose newTrace calls endTap again,
+  // and with the tap still open that recursed until the stack ran out (#378).
   rootKind='';
+  if(kind && answeredAt>rootAt)
+    report('tap',{trace:traceId,span:rootId,start:rootAt,ms:Math.min(answeredAt-rootAt,60_000),msg:kind});
 }
 function newTrace(kind: string){
   endTap();