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fix(overlay): keep a page that reconnects in a background tab alive - #457
Found in an audit of the implicit state machines in the overlay's visibility and reconnect handling (overlay.ts).
A page that reconnects while its tab is hidden can expire on the server.
When the link drops, leave() stops the refresher and clears the hidden heartbeat.
On reconnect, resendConfig() calls onVisibility(), whose hidden branch started with if (!refresher) return;.
With the tab still hidden, the page therefore never reported hidden: true, never started the 60 s hidden heartbeat, and kept its heartbeat paused.
The server's page TTL (rpc/page-ttl.ts, unlimited while hidden or beating) no longer covered it, so the page and its data could expire while the tab was in the background. The same happened after a bfcache pageshow in a hidden tab.
The hidden branch now checks whether the page is already marked hidden (stillHidden), not whether the refresher runs, and both places that clear stillHidden reset it.
A second drop during reconnect restarted everything while offline.overlay-link.ts marks the link online before restored, and the overlay's restored handler awaits claim-page and the redaction config. If the link dropped again in between, leave() ran first, and then resendConfig() still restarted the heartbeat, refresher and collectors offline. A drops counter now makes the handler stand down; the next restored picks up.
How it was verified
New overlay-reconnect-visibility.test.ts:
"reports a page that reconnects in a background tab as hidden and keeps it marked": the page reports hidden: true, sends hidden beats over 130 s, runs no refresher, and resumes normally when visible.
"stays quiet when the link drops again while the page is being claimed": no refresher runs while offline.
overlay-visibility.test.ts: "keeps a hidden tab marked when it comes back from the back/forward cache still hidden"
Each test fails with its fix removed and passes with it
When the link dropped, `leave()` stopped the refresher. On reconnect,
`onVisibility()` returned early in its hidden branch because the
refresher was gone, so a page still in a background tab never reported
itself hidden and never started its hidden heartbeat. The server could
then expire it and drop its data. The hidden branch now checks whether
the page is already marked hidden instead.
A second drop during the `restored` calls (claim-page, redaction) no
longer restarts the heartbeat, refresher and collectors while offline:
the handler stands down when the link dropped again in between.
No actionable comments were generated in the recent review.
Walkthrough
The overlay now tracks hidden-page status across visibility changes and checks for intervening connection drops during reconnect recovery. New tests cover hidden-page reporting, component-tree collection, and watcher behavior during connection outages.
Changes: Overlay visibility and reconnect
Layer / File(s)
Summary
Hidden-page visibility state packages/devtools/src/overlay.ts, packages/devtools/src/__tests__/overlay-visibility.test.ts, packages/devtools/src/__tests__/overlay-reconnect-visibility.test.ts
The overlay tracks whether it has reported the page as hidden, clears that state when visibility returns or the page leaves, and reports hidden status when needed. Tests check hidden reporting and verify that hidden pages do not push component trees or run active watchers.
The overlay counts connection drops and skips applying fetched redaction or resending configuration if another drop occurs during recovery. Tests cover a drop while claim-page is pending and verify that watchers resume after a later successful claim.
pangular-inspector/devtools#437: Adds redaction-config loading and reconnect retry behavior related to the recovery calls checked here.
Suggested labels:area: package
Merge Risk: Minimal · up to c0291
No actionable issue is established; the change is mergeable after normal checks.
Pre-merge checks: 5
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Check skipped - CodeRabbit’s high-level summary is enabled.
Title check
The title describes the main change: keeping a hidden page alive after reconnection.
Docstring Coverage
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
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Full details: Docstring Coverage
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Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 1 functions across 3 files.
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The one red check, "Workers Builds: angular-devtools", isn't from this PR. It's a leftover Cloudflare Worker build that fails on every PR and on main (#431). No fix exists in the repo because it lives in the Cloudflare dashboard. Every other check is green.
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What and why
Found in an audit of the implicit state machines in the overlay's visibility and reconnect handling (
overlay.ts).A page that reconnects while its tab is hidden can expire on the server.
leave()stops the refresher and clears the hidden heartbeat.resendConfig()callsonVisibility(), whose hidden branch started withif (!refresher) return;.hidden: true, never started the 60 s hidden heartbeat, and kept its heartbeat paused.rpc/page-ttl.ts, unlimited while hidden or beating) no longer covered it, so the page and its data could expire while the tab was in the background. The same happened after a bfcachepageshowin a hidden tab.The hidden branch now checks whether the page is already marked hidden (
stillHidden), not whether the refresher runs, and both places that clearstillHiddenreset it.A second drop during reconnect restarted everything while offline.
overlay-link.tsmarks the link online beforerestored, and the overlay'srestoredhandler awaitsclaim-pageand the redaction config. If the link dropped again in between,leave()ran first, and thenresendConfig()still restarted the heartbeat, refresher and collectors offline. Adropscounter now makes the handler stand down; the nextrestoredpicks up.How it was verified
overlay-reconnect-visibility.test.ts:hidden: true, sends hidden beats over 130 s, runs no refresher, and resumes normally when visible.overlay-visibility.test.ts: "keeps a hidden tab marked when it comes back from the back/forward cache still hidden"pnpm test:devtools: 3661 passedpnpm typecheck,pnpm format:check,pnpm commit:checkNo docs change: the behaviour now matches what the docs already describe.
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