[dennev]

When the event loop is blocked long enough for a free socket's idle timeout
to expire, its timeout callback cannot run. The next request can then reuse
that socket from agent.freeSockets even though the server may already have
closed the connection, causing the request to fail with ECONNRESET.

This change addresses the timeout-expiry case discussed in #54293. It records
when a socket enters the free pool using the timers' clock
(timersBinding.getLibuvNow()). In addRequest(), expired candidates are
removed and destroyed until an unexpired socket is found or the pool is empty.

The clock call preserves the binding object as its receiver, as required by
the fast API call. The regression test also exercises an optimized
addRequest().

Not covered by this change:

• free sockets without an idle timeout, including those belonging to agents
  without a timeout (http: Agent with keepAlive and no timeout ignores the server's Keep-Alive timeout hint #66734, http: respect Keep-Alive timeout hint when agent has no explicit timeout #66779)
• a server close still in flight when the request is sent (the general
  keep-alive race discussed in Network request fails after event loop is blocked for a few seconds (regression in v20) #54293)
• a socket handed directly from the 'free' handler to a queued request
• system suspend
• synchronous blocking before the socket enters the free pool, for example
  in a response's 'data' or 'end' handler: the idle timestamp is recorded
  only when the socket enters the pool, so time spent blocked before that
  point is not counted

Testing: I personally ran the regression test on a release build in a Linux
container, and it passed. I also ran a reproduction based on #54293, with
server.keepAliveTimeout = 5000 and a 6-second block between two requests
through http.globalAgent. It fails with ECONNRESET on v26.12.1 and succeeds
with this change, using a new socket.

Agent-run validation confirmed that the regression test fails without this
change and passes with it. It covers LIFO and FIFO expiry, reuse before expiry,
unchanged reuse without an idle timeout, maxSockets accounting after a block,
and optimized addRequest().

Agent-run validation on Linux also included the HTTP/HTTPS and agent-related
tests, and the full make -j12 test, all of which passed. The full-suite run
used a release build in a container started with --init.

AI disclosure: Claude Code (Claude Opus 5.5) was used to investigate the cause,
write and review the code, test and documentation changes, and run the
agent-run validation described above. This description started from a draft
by the agent, which I rewrote. Before opening this pull request, Claude and
Codex (gpt-6.1-sol) reviewed the final change, the commit message and this
description.

I read the change and the new test myself and checked them against the code
paths described above.

Refs: #54293

[nodejs-github-bot]

Review requested:

• @nodejs/http
• @nodejs/net

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[mcollina]

lgtm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.69%. Comparing base (bf246cf) to head (f9ed896).
⚠️ Report is 73 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #67292      +/-   ##
==========================================
- Coverage   90.69%   90.69%   -0.01%     
==========================================
  Files         797      797              
  Lines      278787   279632     +845     
  Branches    53610    53781     +171     
==========================================
+ Hits       252849   253604     +755     
+ Misses      16310    16298      -12     
- Partials     9628     9730     +102     

Files with missing lines	Coverage Δ
lib/internal/http/agent.js	96.75% <100.00%> (+0.11%)	⬆️

... and 68 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78881/