[codex] fix pi home archive restore

[rawkintrevo]

Summary

• exclude Pi runtime-managed $PI_CODING_AGENT_DIR/npm/node_modules from the persisted $HOME archive target
• cover the home archive exclusion behavior with runner unit tests
• document the archive exclusion in the runtime container wiki

Root Cause

pi-basic and related Pi images bake packages such as pi-mcp-adapter into the Pi agent npm tree. Startup then restored the persisted /root archive over that tree before Express started listening. GNU tar could fail on .pi/agent/npm/node_modules/.bin, causing Cloud Run to report that the container never listened on PORT=8080.

Validation

• npm --prefix session-runner test
• npm --prefix session-runner run lint
• npm run docs:check

Browser QA intentionally skipped at user request; user will QA.

Deployment

• FIREBASE_CLI_DISABLE_UPDATE_NOTIFIER=true firebase deploy --only functions --project pi-agents-cloud succeeded. Updated api and reapIdleSessions.
• gcloud builds submit session-runner --project pi-agents-cloud --config session-runner/cloudbuild.pi-basic.yaml succeeded. Pushed session-runner:pi-basic digest sha256:5e65f13ed1d2195002391c27c539cfe34b54bef9294e47526ca70656300e7ce0.

Closes #126

[github-actions]

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