fix(agent-providers): stabilize Copilot and Pi SDK runs

[christso]

Summary

• prefer RuntimeConnection.forTcp() for AgentV-owned Copilot SDK runtimes, falling back to stdio only for older SDKs
• pass PI SDK built-in tool allowlists as tool name strings instead of SDK export objects
• document the Copilot SDK stdio EPIPE rationale in docs/learnings/best-practices/

Why

@github/copilot-sdk@1.0.3 stdio transport can rethrow a child stdin EPIPE after the assistant turn completes, matching upstream github/copilot-sdk#1427. AgentV should avoid that via the SDK-supported TCP transport rather than adding a process-wide exception handler or reaching into private SDK lifecycle fields.

For PI, the current @earendil-works/pi-coding-agent@0.79.10 SDK expects built-in tool selection as names like read, bash, edit, and write. AgentV was constructing a tool object allowlist from exports that are not present in the current SDK.

Validation

• bun test packages/core/test/evaluation/providers/copilot-sdk.test.ts
• bun test packages/core/test/evaluation/providers/pi-coding-agent.test.ts
• bun --filter @agentv/core build && bun --filter agentv build
• git diff --check
• Basic example live provider smoke:
  • examples/features/basic/evals/dataset.eval.yaml --test-id shorthand-string-example --target agentv-pi-sdk-openai: 100% PASS, provider time 6.273s
  • examples/features/basic/evals/dataset.eval.yaml --test-id shorthand-string-example --target agentv-copilot-sdk-openai: 100% PASS, provider time 18.546s

Version checks

• @github/copilot-sdk: local 1.0.3, npm latest 1.0.3
• @github/copilot: local SDK dependency 1.0.64-1; npm latest tag is 1.0.63, prerelease is 1.0.64-3
• @earendil-works/pi-coding-agent: managed local 0.79.10, npm latest 0.79.10
• @earendil-works/pi-ai: nested PI dependency 0.79.10, npm latest 0.79.10

Notes

The heavier Next eval smoke was intentionally replaced with the short examples/features/basic provider smoke after confirming it was a better fit for validating provider wiring quickly.

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