Fifth independent review: realistic tool-call placement

The second terminal acceptance review rejected the corrected candidate after running all requested checks. Continue the same self-update and address these exact findings:

1. In the normal tool loop, the newest durable message is commonly an assistant tool-call message whose content is None or empty, followed by a tool result. The current backward search selects that assistant message, then fails closed because its content is unsupported. The model-visible status is therefore absent during common tool-loop requests.
2. The current test uses assistant tool-call messages with ordinary string content, so it does not cover the production shape above.
3. If the assistant tool-call message does have text, the current code appends status before the following tool result instead of at the request context end. This violates the book/report placement requirement that current model-visible state be closest to generation.

Implement a durable solution at the actual string-only persistence/replay boundary. It may extend string api_content sidecar replay to tool messages if that is supported by the state and flush contracts, but must not widen the database type, mutate clean transcript content, disturb role/tool-call ordering, or attach status to unsupported list/multimodal content. Inspect and test the real production contract rather than relying on a permissive test helper.

Add coverage for an assistant tool call with content=None followed by a string tool result, across at least three successive requests. Assert both byte-identical historical replay and placement after the newest tool evidence. Retain the adversarial output-bound test.

Run the focused tests, existing sidecar/cache/turn-context regressions, compilation, and git diff --check. Update BOOK_SELF_EVOLUTION_REPORT.md with this fifth review and exact results. Do not edit the book, commit, push, or claim downstream task improvement.