fix: guard against null socket/encryption — 'undefined is not a function'

[chris-yyau]

Summary

Fixes intermittent "undefined is not a function" crashes caused by calling methods on null socket/encryption references after WebSocket disconnects.

• apiSocket.ts: Replace this.socket! / this.encryption! non-null assertions with explicit null guards using local variable capture to prevent TOCTOU races across await yield points
• happyMcpStdioBridge.ts: Add promise lock with try/finally to prevent concurrent ensureHttpClient() calls from creating duplicate MCP clients
• startHappyServer.ts: Add server.on('error') handler with logging so port conflicts reject instead of hanging

Test plan

• change_title MCP tool works normally
• App shows "Socket not connected" error instead of crashing on disconnect
• Concurrent change_title calls don't create duplicate clients

🤖 Generated with Claude Code via Happy

[Copilot]

Pull request overview

This PR hardens the Happy app/CLI against intermittent crashes and hangs caused by stale/null references during disconnects and by concurrent initialization paths.

Changes:

• Add explicit null guards and local socket capture in ApiSocket RPC/send paths to prevent “undefined is not a function” after disconnects.
• Serialize MCP HTTP client creation in the STDIO bridge using a shared connectPromise to prevent duplicate clients under concurrent tool calls.
• Reject startHappyServer() startup on server error events so port/bind failures don’t hang silently.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/happy-cli/src/codex/happyMcpStdioBridge.ts	Adds a promise-based lock to prevent concurrent MCP client creation.
packages/happy-cli/src/claude/utils/startHappyServer.ts	Adds an error listener to reject server startup on bind/listen failures.
packages/happy-app/sources/sync/apiSocket.ts	Replaces non-null assertions with runtime guards and safer socket usage across await.

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