Fix 500ms scouting delay regression introduced in 1.7.2

[JafarAbdi]

Description

I was upgrading zenoh for a project I'm working on from 1.7.1 to 1.7.2 and noticed zenoh.open() taking ~500ms longer. Traced it to the gossip refactor in #2347.

What does this PR do?

Move add_peer_connector_zid inside the spawned task, after the transport existence check.

Why is this change needed?

Related Issues

Here is a python script for reproducing the issue

#!/usr/bin/env python3
# /// script
# dependencies = [
#   "eclipse-zenoh==1.7.2",
# ]
# ///
"""Reproduce: zenoh.open() takes ~500ms extra in peer mode due to gossip regression.

Introduced in 1.7.2 by commit 39a440574 ("Fix bugs in gossip (#2347)").
The gossip handler's link_states() adds peer connectors for already-connected
scouted peers that are never terminated, blocking start_conditions.notified()
for the full scouting delay (500ms).

Using eclipse-zenoh==1.7.1 does not have the delay.

Run with:
    uv run reproduce_scouting_delay.py
"""

import multiprocessing
import time

import zenoh


def peer_process():
    """Long-running peer that declares a liveliness token."""
    zenoh.init_log_from_env_or("error")
    config = zenoh.Config.from_json5('{ mode: "peer" }')
    session = zenoh.open(config)
    token = session.liveliness().declare_token("test/alive")

    try:
        while True:
            time.sleep(0.1)
    except KeyboardInterrupt:
        pass
    finally:
        token.undeclare()
        session.close()


def main():
    peer = multiprocessing.Process(target=peer_process, daemon=True)
    peer.start()
    time.sleep(2)  # Wait for peer to be discoverable

    zenoh.init_log_from_env_or("error")
    config = zenoh.Config.from_json5('{ mode: "peer" }')

    start = time.monotonic()
    session = zenoh.open(config)
    elapsed_ms = (time.monotonic() - start) * 1000

    # Verify peer was discovered
    replies = list(session.liveliness().get("test/**", timeout=1.0))
    found = any(r.ok is not None for r in replies)

    print(f"zenoh.open() took {elapsed_ms:.0f}ms (peer found: {found})")
    if elapsed_ms > 100:
        print(f"BUG: expected <100ms, got {elapsed_ms:.0f}ms — scouting delay regression")
    else:
        print("OK: no regression")

    session.close()
    peer.terminate()
    peer.join(timeout=5)


if __name__ == "__main__":
    main()

---

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Labels: bug

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.50%. Comparing base (94123e0) to head (e324a56).
⚠️ Report is 13 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
zenoh/src/net/protocol/gossip.rs	50.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2493      +/-   ##
==========================================
- Coverage   72.58%   72.50%   -0.08%     
==========================================
  Files         390      390              
  Lines       63366    63358       -8     
==========================================
- Hits        45992    45939      -53     
- Misses      17374    17419      +45     

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