fix(worker/ocs): resolve SSE timeout and server startup issues

[aaronwong1989]

Summary

This PR fixes two high-priority issues affecting OpenCode Server worker stability and observability:

Issue #85: SSE Client Timeout Breaks Long-lived Streaming

Problem: SingletonProcessManager created an http.Client with 30s Timeout. The readSSE() goroutine reused this client for SSE requests, causing the long-lived streaming connection to be interrupted after 30s. Additionally, Terminate()/Kill() did not cancel the in-flight SSE HTTP request, leaving the readSSE goroutine blocked.

Solution:

• Add separate sseClient field without Timeout for SSE connections
• Use cancellable context in readSSE() for clean shutdown
• Store sseCancel in Worker and call it in Terminate()/Kill()

Issue #79 Finding 1: Silent HTTP Server Startup Failure

Problem: serverErr channel was created but never read. If HTTP server failed to bind (port in use, permission denied), the error was silently lost. The gateway appeared to start successfully but was actually non-functional.

Solution:

• Use select to race signal against serverErr
• Log error and exit if ListenAndServe fails
• Prevents silent startup failure

Changes

• internal/worker/opencodeserver/singleton.go: Add sseClient field, update Acquire() signature
• internal/worker/opencodeserver/worker.go: Use sseClient, add context cancellation
• cmd/hotplex/gateway_run.go: Handle serverErr channel, remove unused waitForSignal()
• internal/worker/opencodeserver/singleton_test.go: Update for new Acquire() signature

Test Plan

• make test - All tests pass
• make lint - Zero issues
• Manual test: SSE connection remains responsive beyond 30s timeout
• Manual test: Terminate/Kill unblocks readSSE goroutine promptly
• Manual test: Port conflict triggers error log and clean exit

Related Issues

• Fixes fix(worker/ocs): http.Client.Timeout breaks long-lived SSE streams and causes readSSE goroutine leak #85 (SSE timeout)
• Fixes fix(cmd/hotplex): silent HTTP server startup failure and incorrect shutdown exit code #79 Finding 1 (silent startup failure)
• Closes 🐛 Critical Bug: OpenCode Server Worker Session ID Format Incompatibility Causes Gateway Crash #91 (verified as already fixed)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 53.65854% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.55%. Comparing base (a0275ac) to head (9b7fc35).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/worker/opencodeserver/worker.go	37.03%	17 Missing ⚠️
internal/worker/opencodeserver/singleton.go	85.71%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #96      +/-   ##
==========================================
- Coverage   59.56%   59.55%   -0.01%     
==========================================
  Files         134      134              
  Lines       15944    15969      +25     
==========================================
+ Hits         9497     9511      +14     
- Misses       5856     5865       +9     
- Partials      591      593       +2     

Flag	Coverage Δ
unittests	59.55% <53.65%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.