fix(runtime): preserve provider diagnostics on failed turns

[testikun]

Summary

Preserve the bounded, redacted provider response summary for every classified provider failure while keeping the existing error category as the primary presentation. The summary now flows through RuntimeEvent, durable Turn, Runtime Host projections, and Desktop, where it appears collapsed and expandable beneath failed-turn banners for live and reloaded turns. Retry policy and unrelated error semantics remain unchanged.

Fixes #4502

Verification

• Runtime, Runtime Host, Core, and Desktop renderer typechecks pass.
• Biome check passes for all changed source, test, style, and architecture files.
• Runtime Host compatibility epoch guard passes against current apache/main (epoch 99 → 100).
• Renderer architecture check passes against current apache/main.
• Focused runtime adapter/read-model tests pass, including classified failures, retry fixtures, redaction, and 256-byte durable bounds.
• Focused Runtime Host projection tests pass (13 tests).
• Focused UI tests pass (20 tests), including a static render assertion that the provider detail is a collapsed <details> below the classified banner and reload materialization coverage.
• The full runtime suite was also run; 3 unrelated baseline/environment fixtures remain failing (10 tests total across tool-call index, PTY lifecycle, and existing continuation fixtures).

Existing secret redaction and byte bounds are preserved at the provider, durable Turn, Host, and event boundaries.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Codex authored the implementation and regression tests.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No