feat(sdk): return authoritative turn settlement results

[limityan]

Summary

• Return a typed AgentTurnSettlementResult from the Rust Runtime SDK with the authoritative terminal status, final response, and finish reason.
• Keep Core as the result owner: terminal facts are recorded only after successful persistence, with bounded live-session storage and persisted transcript fallback.
• Make SDK Host streaming events progress-only and build the terminal query result from the Runtime settlement result, so intermediate tool-round text cannot be mistaken for the final answer.
• Preserve the existing CLI and App Server wire contracts by consuming or discarding the richer Runtime return value at those adapters.

Scope

• Rust Runtime SDK preview API moves from v9 to v10 because the settlement port return type is source-breaking.
• No custom tool surface, new transport, new process/runtime, dependency addition, or npm/PyPI publication.
• 19 files, 893 insertions and 120 deletions; one commit.

Adversarial review

The review covered persistence failure, cold persisted sessions, transient sessions, recovery generations, rollback/delete/unload invalidation, bounded-cache refresh, timeout priority, unknown-outcome classification, and Host output/cancellation races. The resulting regressions are covered by focused tests.

Validation

• cargo test --locked -p bitfun-runtime-ports --features agent-api — 51 passed
• cargo test --locked -p bitfun-agent-runtime --features agent-runtime --test agent_session_contracts — 67 passed
• cargo test --locked -p bitfun-sdk-host — 66 passed across unit/lifecycle/protocol suites
• Focused bitfun-core settlement, persistence, recovery, projection, and fork/rollback tests — passed
• cargo check --locked -p bitfun-cli --all-targets — passed
• pnpm --dir sdk/typescript test — 66 passed, 1 Unix-only test skipped on Windows
• pnpm run check:core-boundaries — passed
• git diff --check — passed

Known target-branch issue: lightweight_client_negotiates_with_the_production_server fails with missing advertised method session/reloadContext on exact base 21283e2d8 as well as the feature branch. Its lightweight fixture does not register the context-reload port while the assertion requires that dynamically advertised capability; this PR does not alter capability registration. cargo fmt --check likewise reports only five pre-existing formatting diffs outside this PR's changed files.

Implementation and adversarial review used AI assistance. All validation listed above was executed locally.