feat(runtime): preserve reasoning and supported answer text - #1159

The shared runtime dropped backend reasoning and answer text supplied as string-array entries, output_text, or untyped text blocks. Messages now retain a readonly reasoning string and project supported answer text in wire order, while keeping reasoning, media and tool blocks out of the answer.

Reasoning uses explicit event semantics: deltas append, present snapshots replace, and canonical messages/history clear omissions. Missing interim data retains reasoning; independent generations start fresh, while reconnecting the same physical run preserves captured data. Existing ownership and equality make reasoning-only changes observable and equal histories stable. Answer snapshot behavior, message identity and tool authority remain unchanged.

Verification:

• 923 runtime tests in 50 files and runtime/public type checks; 481 public LangGraph tests in 22 files and build.
• Core tests/types/lint, native package builds, 329 parity script tests, inventory, source boundaries and version checks.
• 27 installed browser scenarios per framework, strict declarations and production builds. Removing reasoning projection or restoring the narrow text helper fails the expected assertion in both consumers; exact source restoration and subsequent runs pass.
• Parent independently reran runtime/types and all 54 installed scenarios. Chrome MCP React and in-app Angular walkthroughs verified saved/equal/empty history, separate reasoning and citations, two resumes, canonical clearing and disposal with clean consoles.
• Independent compliance reviews of each slice and a final quality review of the combined change. Source, artifact, negative-control and manual evidence is recorded additively.
• Quality review caught a double-read accessor defect. Seven regressions reproduced coercion/session interruption; accepted block text is now captured once and excluded block getters stay unread. Both independent reviews, runtime/types, installed consumers and manual walkthroughs passed again after the fix.

This is a private runtime migration increment, without a public backend-root cutover, renderer, rich-content contract, timing cache, dependency change or release. The earlier reasoning package evidence explicitly records a later README-only edit; the combined verification rebuilt the packages afterward.