fix a race condition and shutdown in the composite Runnable

[robbyt]

Previously, in runnables/composite/runner.go, the Run() method created a derived runCtx but passed the original ctx to boot(). Then later, boot() launches child goroutines via startRunnable(ctx, ...), which calls context.WithCancel(ctx) per child. Because ctx is the caller's context (not runCtx), the children are not in runCtx's cancellation tree.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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