docs(rfc): enter TypeScript transaction payoff phase

[huangruiteng]

Outcome

Updates the TypeScript control-plane migration RFC from the completed first-cutover plan to the current transaction-payoff phase.

The revised contract records what has shipped through #3416 and #3431-#3443, names the remaining Python facade and bridge debt, and stops flat leaf-helper migration. Future slices must cut over a complete transaction, delete the replaced Python semantic surface, keep Python to one request/one response adaptation, retire migration-only characterization scaffolding, and publish a migration economics receipt.

Migration economics contract

Every later migration PR must report:

• legacy semantic product LOC deleted;
• bridge-only product LOC added;
• happy-path and recovery-path cross-runtime round trips before and after;
• product-code net change separately from tests, fixtures, generated files, and docs;
• characterization scaffolding retained or deleted and its removal trigger;
• the exact condition for deleting the remaining facade.

The RFC names the complete Turn settlement/commit transaction as the first payoff candidate because the current Python settlement surface composes several TypeScript calls and retains duplicate settlement types. It does not authorize a universal reducer or schema framework.

Related surfaces

• semantic-mirror updates to the English and Chinese RFCs;
• technical-directions stage changed to Accepted / transaction-payoff;
• RFC index no longer claims Python remains canonical for migrated semantics.

Validation

• local Markdown links: passed;
• English/Chinese heading structure: passed;
• git diff --check: passed;
• public-safe outbound scan for all five changed files: passed with zero findings;
• DCO sign-off: present;
• full premerge canary: attempted, but the local Codex host remained stuck in Python import after its isolated environment built; terminated without a product failure. Remote clean-runner checks are the merge condition.

Scope

Public documentation only. No runtime behavior, protocol, persistence format, packaging, benchmark, host-adapter, or permission change.

[huangruiteng]

Maintainer validation

Changed surfaces:

• bilingual TypeScript migration RFC;
• architecture RFC index;
• bilingual technical-directions stage entry.

Checks:

• local Markdown links passed;
• bilingual heading structure passed;
• git diff --check passed;
• public-safe outbound scan passed with zero findings;
• remote Sign-off, dependency-review, and build checks passed; deploy correctly skipped for this docs-only change.

Local premerge canary was attempted. Its isolated environment built, but the existing Codex host stalled while importing the CLI after process-table exhaustion; it was terminated without a product assertion or failure. There are no manual product holds. Remote clean-runner checks plus the focused local document and boundary validation are sufficient because this PR changes public architecture documentation only and does not change runtime behavior, protocols, persistence, packaging, permissions, host adapters, benchmarks, or model-visible behavior.

Future-facing pass: applied by replacing the stale first-cutover plan with a transaction-payoff contract, including explicit bridge/scaffolding exit metrics. No runtime abstraction or speculative schema framework was added.