fix(ai): encode system messages as input text

[xianjianlf2]

Fixes #6342

Summary

• encode OpenAI Responses API system/developer messages as typed input_text content
• keep existing role selection for reasoning models
• update request-shape tests for both system and developer roles

Tests

• pnpm test packages/ai/openai/test/OpenAiLanguageModel.test.ts
• pnpm lint-fix
• pnpm check

Summary by CodeRabbit

• Bug Fixes
  • System messages sent through the OpenAI Responses API are now encoded in the expected typed input-text format.
  • Improved compatibility for both standard and reasoning models.

[changeset-bot]

🦋 Changeset detected

Latest commit: 8e21605

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 27 packages

Name	Type
@effect/ai-openai	Patch
effect	Patch
@effect/opentelemetry	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-node-shared	Patch
@effect/platform-node	Patch
@effect/vitest	Patch
@effect/ai-anthropic	Patch
@effect/ai-openai-compat	Patch
@effect/ai-openrouter	Patch
@effect/atom-react	Patch
@effect/atom-solid	Patch
@effect/atom-vue	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-pglite	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-node	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/openapi-generator	Patch

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 8b18314f-0238-418d-8f83-51fae272e72c

📥 Commits

Reviewing files that changed from the base of the PR and between 4e0be58 and 8e21605.

📒 Files selected for processing (3)

• .changeset/fix-openai-system-input-text.md
• packages/ai/openai/src/OpenAiLanguageModel.ts
• packages/ai/openai/test/OpenAiLanguageModel.test.ts

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📝 Walkthrough

Walkthrough

OpenAI Responses system messages now use typed input_text content arrays. Tests verify the updated system and developer message shapes, and a patch changeset documents the provider change.

Changes

OpenAI system input text

Layer / File(s)	Summary
Typed input text encoding packages/ai/openai/src/OpenAiLanguageModel.ts, packages/ai/openai/test/OpenAiLanguageModel.test.ts, .changeset/fix-openai-system-input-text.md	System message content is wrapped as an OpenAI input_text array, tests assert the updated system and developer request shapes, and a patch changeset records the change.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested labels: bug

Suggested reviewers: tim-smart

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR encodes system and developer messages as typed input_text content while preserving role selection, matching issue #6342.
Out of Scope Changes check	✅ Passed	The changes stay focused on Responses API message encoding and matching tests/changeset, with no unrelated code paths altered.

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