Fix session leak when context canceled during async creation

[Copilot]

When context is canceled while a session is being created asynchronously, the session was added to the pool index but never properly cleaned up, causing the pool to grow beyond configured limits.

Root Cause

In makeAsyncCreateItemFunc, the background goroutine adds newly created items to p.index immediately after creation. When the caller's context is canceled before receiving the item:

1. The item remains in p.index
2. The goroutine attempts putItem() on an item the caller never received
3. Pool metrics show items in index but createInProgress is decremented, allowing limit violations

Changes

• internal/pool/pool.go: In the <-done case, remove item from index and close it directly instead of calling putItem()
• internal/pool/pool_test.go: Add ContextCanceledDuringCreate test covering both race conditions:
  • Item created before context check (returned to caller)
  • Context canceled before item creation (removed and closed)

case <-done:
    if newItem == nil {
        return
    }
    // Remove from index and close directly
    p.mu.WithLock(func() {
        delete(p.index, newItem)
    })
    closeCtx := createCtx
    if t := p.config.closeTimeout; t > 0 {
        var cancel context.CancelFunc
        closeCtx, cancel = context.WithTimeout(closeCtx, t)
        defer cancel()
    }
    p.config.closeItemFunc(closeCtx, newItem)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>bug: Session leak. Growth beyond the configured limits in the pool.</issue_title>
<issue_description># Bug Report

v3.118.1

Environment

go1.25.4 linux/amd64

Current behavior:

If the context is canceled early, the created session is not counted in the limits and is not closed on the server.

Expected behavior:

The total number of sessions does not exceed the specified limits.

Related code:

Example playback repository

Other information:

Screencast demo
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes bug: Session leak. Growth beyond the configured limits in the pool. #1934

---

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.14%. Comparing base (3c5460f) to head (64885fd).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1982   +/-   ##
=======================================
  Coverage   74.14%   74.14%           
=======================================
  Files         395      395           
  Lines       34598    34606    +8     
=======================================
+ Hits        25654    25660    +6     
+ Misses       7825     7820    -5     
- Partials     1119     1126    +7     

Flag	Coverage Δ
experiment	73.82% <100.00%> (-0.04%)	⬇️
go-1.21.x	72.99% <100.00%> (-0.06%)	⬇️
go-1.25.x	74.14% <100.00%> (+<0.01%)	⬆️
integration	55.07% <0.00%> (-0.33%)	⬇️
macOS	47.77% <100.00%> (-0.02%)	⬇️
ubuntu	74.14% <100.00%> (+<0.01%)	⬆️
unit	47.79% <100.00%> (+<0.01%)	⬆️
windows	47.77% <100.00%> (-0.02%)	⬇️
ydb-24.4	54.25% <0.00%> (-0.30%)	⬇️
ydb-25.2	54.98% <0.00%> (-0.34%)	⬇️
ydb-latest	54.66% <0.00%> (-0.31%)	⬇️
ydb-nightly	73.82% <100.00%> (-0.04%)	⬇️

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[github-actions]

summary

Inferred base version: v3.123.1
Suggested version: v3.123.2