Ensure a summarizer stop request is respected after connecting

[kian-thompson]

When taking a look at summarizer telemetry, I observed a weird race condition around connection and last summaries. If the parent disconnects and reconnects before the summarizer finishes loading then it won't stop as the parent expects.

Example flow:

1. Parent is elected
2. Start loading summarizer
3. Parent disconnects
4. Attempt to call summarizer?.stop(...) does nothing since the summarizer has not finished loading (see createSummarizerFn())
5. Parent reconnects
6. Summarizer finishes loading and returns instance to parent
7. Summarizer doesn't recognize that it was supposed to stop, so it continues to live as normal
8. Parent hits "SummarizerStopTimeout" since it expected its summarizer to stop

This PR adds a stop check right after step 6.

AB#61863

[Copilot]

Pull request overview

This PR fixes a race where a stop request (triggered while the summarizer is still being created) could be lost, causing the summarizer to continue running and eventually hit SummarizerStopTimeout. It adds a mechanism to remember the stop reason during async summarizer creation and replay it immediately once the summarizer instance is available.

Changes:

• Track a pending stop reason while awaiting createSummarizerFn() and replay it immediately after the summarizer is created.
• Clear pending stop intent during cleanup/dispose to avoid cross-cycle contamination.
• Add a targeted unit test covering “stop requested before summarizer creation completes” and validating last-summary behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/runtime/container-runtime/src/summary/summaryManager.ts	Adds pendingStopReason to persist and replay stop intent after async summarizer creation.
packages/runtime/container-runtime/src/test/summary/summaryManager.spec.ts	Adds a regression test for the stop-before-create race and test plumbing to observe stop reason + summarize events.

[shlevari]

Approved with suggestions for added comment