fix(desktop): push local backend topology changes instead of polling over IPC

[otavio]

Problem

The desktop renderer reads getLocalEnvironmentBootstraps() from the main process on timers: the connection platform every 3 s, and useDesktopLocalBootstraps every 2 s for each mounted consumer. The bridge had no change event. Each read is a synchronous IPC call. It blocks the renderer whenever the main process is busy, which causes the Windows typing stalls in #12689. Each read also writes four desktop trace spans, plus getLocalEnvironmentEnabled on every tick, so an idle app fills desktop.trace.ndjson (#19505).

Fix

Two commits:

1. Daniyal's fix(desktop): stop blocking the renderer during topology polling #19300, cherry-picked unchanged. The preload caches the topology snapshot, and getLocalEnvironmentEnabled is read once per launch.
2. The desktop pushes topology changes instead of the renderer polling.
   • The backend manager's lifecycle state and the pool registry are now SubscriptionRefs. The pool exposes their combined changes.
   • A main-process forwarder recomputes the bootstraps on every change. It also recomputes at each bootstrap-token window boundary, checking at least hourly so a boundary passed during system sleep is caught soon after resume. It pushes on desktop:local-environment-bootstraps only when the result differs.
   • The preload writes pushed values into fix(desktop): stop blocking the renderer during topology polling #19300's cache. After the first read, getLocalEnvironmentBootstraps() costs no IPC.
   • The bridge API is now one cached read plus one subscription: getLocalEnvironmentBootstraps() and onLocalEnvironmentBootstrapsChange(listener). Because the push keeps the cache current, fix(desktop): stop blocking the renderer during topology polling #19300's async readLocalEnvironmentBootstraps refresh is no longer needed. This PR removes it, so platform.ts matches main apart from a comment.
   • useDesktopLocalBootstraps re-reads on the event and no longer has an interval. The platform's 3 s tick stays for discovery retries and bearer refresh, but it now reads only the cache.

This supersedes #19300 and the closed #12698, with credit to @daniyal-sh, whose commit is kept as-is, and @hnasser22 for the original investigation.

Reproduction

Reproduced on Linux (NixOS, T3 Code Nightly desktop, Electron 44.5.1), both on my everyday install and on a sandboxed dev build of main:

• Everyday install: desktop.trace.ndjson shows, every 3.0 s, one getLocalEnvironmentEnabled and two getLocalEnvironmentBootstraps calls in the same millisecond, about 1,270 such ticks per rotated file. That is the platform poll described in the [Bug]: Windows desktop typing lags even in empty chats; browser interface is smooth #12689 triage.
• Sandboxed main: shows the same pattern: 100 ticks with 2 reads each in a 300 s idle window, all over invokeSync.

This reproduces the trace flooding (#19505) and the recurring synchronous IPC that #12689 identifies as the cause of its typing stalls. I did not reproduce or measure the typing stall itself.

Verification

Focused tests, typecheck and lint:

apps/desktop$ vp test run src/preloadSnapshot.test.ts src/ipc/methods/window.test.ts src/backend/DesktopBackendPool.test.ts src/backend/DesktopBackendManager.test.ts src/wsl/DesktopWslBackend.test.ts src/updates
 Test Files  11 passed (11)
      Tests  138 passed (138)
apps/web$ vp test run src/connection/useDesktopLocalBootstraps.test.tsx src/connection/desktopLocal.test.ts src/connection/platform.test.ts
 Test Files  3 passed (3)
      Tests  29 passed (29)
vp run --filter @t3tools/desktop --filter @t3tools/web --filter @t3tools/contracts typecheck   # pass
vp lint <changed files>        # exit 0
vp fmt --check <changed files> # all files formatted

New tests:

• The forwarder pushes only changed bootstraps, sends nothing after a failed read and keeps forwarding afterwards, and pushes the new token at the window boundary. It runs on TestClock with no sleeps.
• The pool's changes fires on register and unregister.
• The preload cache needs one sync read, a push before that read skips it, and a failed read is retried.
• The hook re-reads on the event and makes no reads across 60 s of fake timers. A failed read keeps the last snapshot, and a successful empty read clears it.
• Mutation check: removing the forwarder's dedupe, or putting the hook's 2 s interval back, makes the matching test fail.

Real desktop trace (Linux, Electron 44.5.1, vp run dev:desktop):

• Setup: isolated --home-dir sandboxes seeded with migrate-dev-db, and an idle window with the sidebar visible.
• Before: main @ 7ac952c.
• After: this branch.
• Measurement window: 300 s, starting 60 s after the first desktop span.

	Before	After
desktop.ipc.window.getLocalEnvironmentBootstraps	200 (0.67/s)	0
desktop.backendConfiguration.resolvePrimaryLabel	200	0
desktop.ipc.invokeSync	300	0
desktop.ipc.localEnvironment.getEnabled	100	0
All desktop spans	1,130	30

Whole-file jq -r .name desktop.trace.ndjson* | sort | uniq -c | sort -rn | head. The after run also includes a backend restart:

before                                              after
406 desktop.ipc.method                              258 desktop.observability.writeBackendChildLogRecord
364 desktop.ipc.invokeSync                           94 desktop.ipc.registerInvoke
237 desktop.ipc.window.getLocalEnvironmentBootstraps 65 desktop.ipc.method
237 desktop.backendConfiguration.resolvePrimaryLabel 60 desktop.ipc.invoke
124 desktop.ipc.localEnvironment.getEnabled          27 desktop.ipc.preview.setForwardedShortcuts
 94 desktop.ipc.registerInvoke                       21 desktop.ipc.window.getLocalEnvironmentBootstraps
 42 desktop.ipc.invoke                               20 GET
 19 desktop.ipc.preview.setForwardedShortcuts        20 desktop.backendConfiguration.resolvePrimaryLabel
 13 desktop.ipc.snapShot.listPending                 18 desktop.ipc.snapShot.listPending
 13 desktop.ipc.snapShot.ensureTrustedSender         18 desktop.ipc.snapShot.ensureTrustedSender

In the after run, all 21 bootstrap reads came from startup and from the restart: 12 main-side recomputes during the restart, and none from the renderer.

Manual check, after run:

• Backend restart: I killed the backend process. The desktop restarted it, recomputing the bootstraps 12 times on lifecycle events, with 0 renderer invokeSync. URL and token were unchanged, so nothing was pushed.
• Sidebar: still listed the local environment's projects and threads after the restart.
• Command palette: opened normally. With it open, so the hook was mounted, the desktop wrote 0 spans in 20 s.

Not covered here:

• A live topology change, such as a WSL backend or a new port, is not reachable on Linux. Unit tests cover push delivery for that path.
• Typing latency for [Bug]: Windows desktop typing lags even in empty chats; browser interface is smooth #12689 was not profiled on Windows or Linux. This PR removes the recurring sync IPC entirely: the after run made 0 renderer invokeSync calls while idle. A Windows typing profile from someone affected would confirm the stall is gone.

Fixes #19505
Refs #12689
Supersedes #19300

Implemented with Claude Opus 5.5 in T3 Code through the Claude Code harness.

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📥 Commits

Reviewing files that changed from the base of the PR and between d526d08 and 7690ece.

📒 Files selected for processing: 2

• apps/web/src/connection/useDesktopLocalBootstraps.test.tsx
• apps/web/src/connection/useDesktopLocalBootstraps.ts

🚧 Files skipped from review as they are similar to previous changes: 1

• apps/web/src/connection/useDesktopLocalBootstraps.test.tsx

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📝 Walkthrough

Desktop backend changes now drive bootstrap snapshot pushes through main-process IPC into a preload cache. The desktop bridge exposes change notifications. The web hook subscribes when supported and polls every two seconds for older bridges.

Changes: Local Environment Bootstrap Updates

Layer / File(s)	Summary
Backend change streams apps/desktop/src/backend/DesktopBackendManager.ts, apps/desktop/src/backend/DesktopBackendPool.ts, apps/desktop/src/backend/*.test.ts, apps/desktop/src/updates/updatesTestHarness.ts, apps/desktop/src/wsl/DesktopWslBackend.test.ts	Backend instances expose lifecycle change streams, and the pool emits changes when its registry or active instances change. Tests and fixtures provide and verify those streams.
Main-process snapshot forwarding apps/desktop/src/ipc/methods/window.ts, apps/desktop/src/ipc/methods/window.test.ts, apps/desktop/src/ipc/DesktopIpcHandlers.ts, apps/desktop/src/ipc/channels.ts	The main process sends changed bootstrap snapshots after backend changes or token-window ticks. It suppresses duplicate snapshots and logs read failures without ending forwarding.
Preload cache and bridge contract apps/desktop/src/preload.ts, apps/desktop/src/preloadSnapshot.ts, apps/desktop/src/preloadSnapshot.test.ts, packages/contracts/src/ipc.ts	The preload caches bootstrap snapshots and updates the cache from IPC events. The bridge adds an optional change listener, and the snapshot helper caches successful reads and retries after failures.
Web change subscription apps/web/src/connection/useDesktopLocalBootstraps.ts, apps/web/src/connection/useDesktopLocalBootstraps.test.tsx, apps/web/src/connection/platform.ts, docs/internals/performance-regressions.md	The hook reads bootstrap snapshots on change notifications instead of polling when the bridge supports events. It polls for older bridges. Tests cover snapshot updates and listener cleanup.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant DesktopBackendPool
  participant BootstrapForwarding
  participant RendererWindows
  participant PreloadCache
  participant DesktopHook
  DesktopBackendPool->>BootstrapForwarding: Emit backend change
  BootstrapForwarding->>RendererWindows: Send changed bootstrap snapshot
  RendererWindows->>PreloadCache: Deliver IPC payload
  PreloadCache->>DesktopHook: Notify bootstrap change
  DesktopHook->>PreloadCache: Read cached snapshot

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Merge Risk: ⚪ Minimal · up to 7690e

Newer desktop bridges refresh bootstrap snapshots from change notifications, while older bridges retain the tested polling fallback. No specific merge-blocking behavior remains.

Security architecture risk: 🔵 Low · up to 7690e

No new authorization bypass was established. However, a failed update can leave local connection information stale, and credential-bearing updates reach windows that do not need them.

Retained concerns

• Low · reliability · inferred: Failed broadcast delivery can strand healthy renderers on an earlier topology or bootstrap credential. The forwarder records lastSent before delivery; sendAll stops on the first send exception, and later identical snapshots are suppressed. This weakens failure containment between unrelated windows and removes the former fresh-read recovery path.

Security review details

Security Blast Radius

• observed — Each pushed snapshot covers registered pool instances with bootstrap information, potentially including primary and WSL backends. Delivery uses the global BrowserWindow set rather than only trusted desktop bridge consumers. Preview HTTP/HTTPS popups can therefore receive the transport message, although receipt does not establish page-level access to its contents.

Security Findings and Attack Paths

• inferred — An attacker-controlled preview page can cause an HTTP/HTTPS popup to join the broadcast recipient set, but the inspected source does not establish a page-accessible bootstrap getter or event listener there. A credential-theft path would require an additional IPC, preload, or renderer-isolation bypass; the broadcast alone is not a verified authorization bypass.

Trust Boundaries and Controls

• observed — The main application window runs with sandboxing, context isolation, and disabled Node integration. It denies native window creation from its page and blocks cross-origin navigation. Preview popups separately enforce sandboxing, context isolation, and disabled Node integration; their pages do not inherit the main desktop bridge merely by receiving a broadcast.

Resilience and Maintainability Implications

• inferred — Logging forwarding failures keeps the stream alive but does not restore an identical failed delivery. This can delay topology discovery or authenticated reconnection in otherwise healthy windows. A distinct later snapshot can repair the cache, and existing bearer-retention and token-overlap rules reduce immediate disruption; cached polling does not itself repair missed delivery.

Hardening Proposals

• proposed — Restrict credential-bearing bootstrap delivery to explicitly authorized desktop bridge windows. This would reduce unnecessary dissemination into auxiliary and external-content renderer processes; it is defense in depth, not evidence that those pages can currently read the credentials.

Pre-merge checks: 3 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Description check		The description provides detailed problem context, implementation details, reproduction steps, verification results, measurements, and limitations. However, it uses a "Fix" heading instead of the requ…	Add the required "## Change" section or rename "## Fix" to "## Change". Add a complete "## Scope and approval" section with the triaged issue or approval discussion, including explicit maintainer approval and the approval comment. If claimi…

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: replacing renderer polling over IPC with push-based local backend topology updates.
Linked Issues check		Issues #12698 and #19505 are closed. They provide historical context only. No active directly linked target supplies coding requirements. The reported implementation and tests are consistent with the …
Out of Scope Changes check		The changes stay within the local-environment topology update scope. Backend change streams, main-process forwarding, token-boundary refresh, preload caching, bridge subscription, renderer event handl…

Full details: Description check

Explanation

The description provides detailed problem context, implementation details, reproduction steps, verification results, measurements, and limitations. However, it uses a "Fix" heading instead of the required "Change" heading and does not provide the required Scope and approval information, such as a triaged issue with explicit maintainer approval or a valid small-fix exemption.

Resolution

Add the required "## Change" section or rename "## Fix" to "## Change". Add a complete "## Scope and approval" section with the triaged issue or approval discussion, including explicit maintainer approval and the approval comment. If claiming a small-fix exemption, explain why this change qualifies.

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Inline comments:
Review comments at @apps/web/src/connection/useDesktopLocalBootstraps.ts:
- Line 21: Update the subscription setup in the effect containing
`onLocalEnvironmentBootstrapsChange` to use the listener when available and
otherwise poll `read` every two seconds. Return cleanup that clears the fallback
interval, preserving ongoing bootstrap updates on older desktop shells.

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📥 Commits

Reviewing files that changed from the base of the PR and between 7ac952c and d526d08.

📒 Files selected for processing: 18

• apps/desktop/src/backend/DesktopBackendManager.test.ts
• apps/desktop/src/backend/DesktopBackendManager.ts
• apps/desktop/src/backend/DesktopBackendPool.test.ts
• apps/desktop/src/backend/DesktopBackendPool.ts
• apps/desktop/src/ipc/DesktopIpcHandlers.ts
• apps/desktop/src/ipc/channels.ts
• apps/desktop/src/ipc/methods/window.test.ts
• apps/desktop/src/ipc/methods/window.ts
• apps/desktop/src/preload.ts
• apps/desktop/src/preloadSnapshot.test.ts
• apps/desktop/src/preloadSnapshot.ts
• apps/desktop/src/updates/updatesTestHarness.ts
• apps/desktop/src/wsl/DesktopWslBackend.test.ts
• apps/web/src/connection/platform.ts
• apps/web/src/connection/useDesktopLocalBootstraps.test.tsx
• apps/web/src/connection/useDesktopLocalBootstraps.ts
• docs/internals/performance-regressions.md
• packages/contracts/src/ipc.ts

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[maria-rcks]

Note

Written by gpt-6.1-sol on behalf of Maria

Thanks for investigating the recurring IPC calls and trace flooding. Right now we are only taking focused bug fixes from outside contributors under our limited review capacity. This 642-line change across 18 files replaces backend state tracking and adds topology forwarding, which is too large for us to take over. Please preserve the trace-flooding evidence in #19505 and request reconsideration with a much smaller fix for that verified defect.