test(pubsub): add regression coverage for subscribe race edges

[Faolain]

Summary

This PR adds focused pubsub regression coverage based on historical issues discussed in #596.

master already has coverage for:

• immediate pending-subscribe tracking / local cleanup
• strict direct delivery while subscribe is pending

But it did not have explicit regression tests for a few race/design edges that #596 attempted to protect.

What this adds

New file:

• packages/transport/pubsub/test/subscribe-races.spec.ts

New regression tests:

1. concurrent subscribe + connect

• Verifies peers still discover each other when subscribe() and connect() happen concurrently.

2. non-subscriber topic tracking guard

• Verifies a peer that never subscribed does not start tracking a topic just from incoming subscription traffic.

3. cancelled pending subscription is not advertised

• Verifies subscribe() followed by unsubscribe() within the debounce window does not leave stale remote subscriber state.

Why these tests are useful

These are race-sensitive behaviors that are easy to regress during refactors around:

• subscription debounce/pending state handling
• topic map lifecycle
• fanout control-plane synchronization during connect/subscribe interleaving

They complement existing fanout-topics.spec.ts checks by asserting network-visible behavior (peer discovery / non-discovery), not only local state transitions.

Notes from PR #596 analysis

• The old requestSubscribers while remote _subscribe() is blocked scenario from PubSub pendingSubscriptions + SharedLog replication handshake hardening #596 still fails on current master when enabled.
• That case is not added as an active test in this PR because it currently represents behavior that would require implementation changes, not just regression guarding.

Verification

Run:

node ./node_modules/aegir/src/index.js run test --roots ./packages/transport/pubsub -- -t node

Result locally: passing (53 passing).

Looped regression test 50 times and it passes every time.

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[marcus-pousette]

Thanks for this, the direction is good and the added race coverage is valuable

I have two test-hardening requests before merge:

1. packages/transport/pubsub/test/subscribe-races.spec.ts:95
   The delay(250) + negative assertion can false-pass on slow/partial propagation. Please anchor this test on an observed subscribe/control-plane event (or a waitForResolved condition that proves B actually reached subscribed state) before asserting A does not track the topic.

2. packages/transport/pubsub/test/subscribe-races.spec.ts:133
   The if (bTopics) branch makes the key assertion optional. Please make it strict:

   • assert bTopics exists
   • assert bTopics does not contain a.publicKeyHash

With those tightened, I’m +1 to merge.

[Faolain]

Updated! Also I checked off to allow maintainers edit access so feel free to modify my commit as you wish if it's faster!

[marcus-pousette]

👍👍

[marcus-pousette]

Reviewed: regression coverage is valuable and aligns with current pubsub behavior. Approving.