Plain workspaces keep an unbounded recursive watcher alive after #1779

[MateoCerquetella]

Summary

bb-app 0.39.0 OOMed a Linux host because bb-parcel-watcher-child.mjs grew to about 11.4 GiB RSS while remaining responsive. PR #2041 substantially reduced the recursive tree by ignoring nested .git, node_modules, and caches, but current main still starts a recursive Parcel subscription for every non-Git workspace even though the only Git-status transition it needs to detect is <root>/.git appearing; the proxy also treats a pong as healthy regardless of RSS.

Expected: a plain workspace should detect git init without recursively indexing its entire tree, and a responsive native watcher should be recycled before it can OOM the whole service.

Versions and environment

• Incident: bb-app 0.39.0 installed globally and managed by a systemd user service
• Linux 6.18.42-1-cachyos-lts x86_64
• Node v22.23.1
• 25 GiB RAM and 25 GiB swap
• Current-main inspection/repro: 494f66526913557ab076e048218236f0a6610927
• Unmanaged non-Git environments included /home/dyaus and /home/dyaus/Developer, with several nested project environments

Steps to reproduce

1. Register or open environment detail for an unmanaged non-Git workspace rooted at a broad directory such as a home or developer directory.
2. Observe that WorkspaceStatusWatcher.startAsync() calls startWatchSubscription() for that root even though .git does not exist.
3. Observe bb-parcel-watcher-child.mjs RSS while the environment remains subscribed. Pongs continue, so the proxy does not recycle it for memory growth.
4. Unit-level current-main repro: assert that @parcel/watcher.subscribe is not called before git init; the assertion fails because one recursive subscription is installed immediately.

I did not intentionally reproduce the 11 GiB endpoint on current main; doing so risks another shared-host OOM. The structural plain-root subscription and absence of an RSS ceiling are both present at the commit above.

Expected vs actual

Actual incident output:

oom-kill:constraint=CONSTRAINT_NONE,...,task_memcg=/user.slice/user-1000.slice/user@1000.service/app.slice/bb-primary.service,task=node,pid=1044,uid=1000
Out of memory: Killed process 1044 (node) total-vm:33655680kB, anon-rss:11988468kB, file-rss:40160kB, shmem-rss:0kB
bb-primary.service: Failed with result 'oom-kill'.
bb-primary.service: Consumed 1h 59min 752ms CPU time over 11h 56min 28.490s wall clock time, 16.6G memory peak, 20.8G memory swap peak.

Current-main regression output:

AssertionError: expected [ [Function] ] to have a length of +0 but got 1

Expected: no recursive Parcel subscription while the workspace is non-Git; git init promotion still occurs promptly; a sustained high-RSS child cannot OOM the service.

Evidence

• Follow-up to Recursive workspace watch can OOM the host for a large environment root #1779 and merged mitigation Ignore nested node_modules and .git in the workspace root watch #2041.
• Current plain-workspace subscription:

  bb/packages/host-watcher/src/workspace-status-watcher.ts

  Lines 249 to 260 in 494f665

  	return;
  	}
  	if (!(await pathExists(path.join(this.args.cwd, ".git")))) {
  	// A plain workspace can become a repository after `git init`. Watch the
  	// root without excluding `<root>/.git` until that marker appears, but
  	// still skip nested repositories and heavy directories.
  	this.startWatchSubscription({
  	kind: "workspace-root",
  	options: { ignore: createPlainWorkspaceRootIgnores() },
  	rootPath,
  	});
  	return;

• Current liveness-only pong handling:

  bb/packages/host-watcher/src/parcel-subprocess/parcel-watcher-proxy.ts

  Lines 245 to 249 in 494f665

  	}
  	function handleChildMessage(
  	source: ChildChannel,
  	message: ChildToParentMessage,

• Kernel RSS was measured from the OOM record; service peaks are systemd accounting values.

What you ruled out

• Not a duplicate of Recursive workspace watch can OOM the host for a large environment root #1779: Ignore nested node_modules and .git in the workspace root watch #2041 added recursive ignore globs; this follow-up removes the unnecessary plain-root subscription and adds a supervisor memory bound.
• The production incident happened on 0.39.0, which predates Ignore nested node_modules and .git in the workspace root watch #2041; this report does not claim the same 11 GiB endpoint was reproduced after that merge.
• Not an application server heap failure: the OOM victim was the isolated native Parcel watcher child in the BB service cgroup.
• Provider-independent: the failure is in host workspace watching.

Suggested priority and effort

High impact when triggered because the entire BB service is killed; workaround is to avoid broad non-Git environment roots. Estimated medium effort.

AGENT GENERATED

[MateoCerquetella]

Closing this follow-up: the watcher fix is already in nightly and is planned for the next stable release, so no additional PR is needed.\n\n> AGENT GENERATED