fix(openai): fail degraded streaming results

[im10furry]

Summary

• fail OpenAI-compatible streams that end before usable assistant output instead of returning successful (no content) results
• preserve partial assistant output only when the stream degrades after usable content/tool calls and mark the assistant turn as an API error
• make print and persistent stream-json results report degraded/API-error assistant turns as error_during_execution with is_error: true
• filter API-error assistant messages out of future API input normalization

Verification

• bun test ./packages/core/src/test/unit/openai-stream-abort.test.ts ./packages/core/src/test/unit/stream-json-session.test.ts ./packages/core/src/test/unit/messages-normalization-reorder.test.ts ./packages/core/src/test/unit/print-mode-api-error.test.ts
• git diff --check
• bunx prettier --check packages/core/src/ai/openai/stream.ts packages/core/src/ai/llm/openai/stream.ts packages/core/src/ai/llm/openai/queryOpenAI.ts apps/cli/src/entrypoints/cli/print/runSingleTurn.ts packages/protocol/src/utils/kodeAgentStreamJsonSession.ts packages/core/src/test/unit/openai-stream-abort.test.ts packages/core/src/test/unit/stream-json-session.test.ts packages/core/src/test/unit/messages-normalization-reorder.test.ts packages/core/src/test/unit/print-mode-api-error.test.ts
• bunx eslint --max-warnings 0 packages/core/src/ai/openai/stream.ts packages/core/src/ai/llm/openai/stream.ts packages/core/src/ai/llm/openai/queryOpenAI.ts apps/cli/src/entrypoints/cli/print/runSingleTurn.ts packages/protocol/src/utils/kodeAgentStreamJsonSession.ts packages/core/src/test/unit/openai-stream-abort.test.ts packages/core/src/test/unit/stream-json-session.test.ts packages/core/src/test/unit/messages-normalization-reorder.test.ts packages/core/src/test/unit/print-mode-api-error.test.ts
• bun run typecheck