feat(proxyrunner): wire SIGTERM-aware graceful shutdown (RC-14)

[yrobla]

Summary

Replace Execute() with signal.NotifyContext + ExecuteContext() in cmd/thv-proxyrunner/main.go, mirroring cmd/vmcp/main.go. SIGTERM, SIGQUIT, and os.Interrupt now cancel the root context so in-flight MCP proxy connections drain via transportHandler.Stop instead of being dropped abruptly during Kubernetes pod termination.

Fixes #4207

Type of change

• Bug fix
• New feature
• Refactoring (no behavior change)
• Dependency update
• Documentation
• Other (describe):

Test plan

• Unit tests (task test)
• E2E tests (task test-e2e)
• Linting (task lint-fix)
• Manual testing (describe below)

Changes

File	Change

Does this introduce a user-facing change?

Special notes for reviewers

[Copilot]

Pull request overview

This PR updates the thv-proxyrunner entrypoint to propagate a signal-cancellable root context into Cobra execution so Kubernetes termination signals trigger the existing graceful drain path (context cancellation → runner stop → transportHandler.Stop) rather than abrupt termination.

Changes:

• Add signal.NotifyContext in cmd/thv-proxyrunner/main.go to cancel on os.Interrupt, SIGTERM, and SIGQUIT.
• Switch from Execute() to ExecuteContext(ctx) and log/exit on command execution errors.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.95%. Comparing base (3ae086f) to head (c7b5470).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4241      +/-   ##
==========================================
- Coverage   69.29%   68.95%   -0.35%     
==========================================
  Files         470      473       +3     
  Lines       47197    47854     +657     
==========================================
+ Hits        32706    32997     +291     
- Misses      11957    12266     +309     
- Partials     2534     2591      +57     

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[Copilot]

Pull request overview

Adds SIGTERM-aware graceful shutdown handling to the thv-proxyrunner entrypoint so Kubernetes pod termination signals cancel the root context and allow the runner’s existing drain/stop path to execute.

Changes:

• Update cmd/thv-proxyrunner/main.go to use signal.NotifyContext(...) and ExecuteContext(ctx) (SIGTERM/SIGQUIT/Interrupt cancel the root context).
• Add a new e2e test that starts thv-proxyrunner, waits for the proxy port to accept connections, sends SIGTERM, and asserts shutdown.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
cmd/thv-proxyrunner/main.go	Wires OS-signal cancellation into the Cobra root command via ExecuteContext.
test/e2e/proxyrunner_graceful_shutdown_test.go	Adds an e2e scenario for SIGTERM-driven shutdown behavior of thv-proxyrunner.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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fixed