chore: persist reasoning content on events for consitent replay

[sr07asthana]

Summary

Closes #

Changes

How was this tested?

Checklist

• I have read the contributing guidelines
• pnpm build, pnpm test, pnpm typecheck, pnpm lint:ci, and pnpm format:check pass locally
• Tests added/updated where it makes sense
• No hand-edits to generated code (packages/trueforge-sdk, .github/fern/openapi/openapi.json, docs/openapi.json) — fork PRs omit SDK regen; maintainers regenerate after merge
• Docs / .env.example updated if configuration or behavior changed

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Note

Low Risk
Localized LLM streaming and context persistence behavior with explicit tests; no auth or data-path changes beyond what is stored on thread context vs events.

Overview
Reasoning text is now stored end-to-end for UI replay while multi-turn LLM context still relies on thinking_blocks only.

Streaming assembly in VercelAILLM concatenates reasoning deltas into accumulatedReasoning and sets reasoning_content on the final assistant message, matching what the client saw in SSE chunks. Schema comments were updated to describe that split (deltas vs assembled field).

After completion, AgentThread strips reasoning_content before appendToContext so persisted thread history does not duplicate display-only reasoning; model.message events keep reasoning_content (and continue to omit thinking_blocks for folded-stream parity). Tests cover stream output and the context vs event split.

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🦋 Changeset detected

Latest commit: 5bd78d3

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

This PR includes changesets to release 2 packages

Name	Type
@truefoundry/trueforge-core	Patch
@truefoundry/trueforge	Patch

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