feat(translator,executor): preserve Kimi reasoning as canonical reasoning_content

[warelik]

Summary

Preserves Kimi reasoning as canonical reasoning_content when translating Claude requests to OpenAI-compatible targets.

• internal/translator/openai/claude/openai_claude_request.go shouldMapClaudeThinkingToReasoning: when target is a Kimi model, degrade Claude thinking blocks to unsigned reasoning_content instead of dropping foreign or unsigned signed blocks. GPT and unknown targets keep existing strict behavior.
• internal/runtime/executor/helps/codex_multi_agent_v2.go TranslateRequestWithAPIKeyModelCompatibility: skip CarryOverThinkingToSystem for Kimi targets so prior reasoning_content stays in assistant messages rather than being moved into a system message.
• internal/runtime/executor/helps/carry_over.go: carry-over helper for reasoning and plugin-payload doc comment.
• internal/runtime/executor/kimi_executor.go fallbackAssistantReasoning: do not copy visible assistant content into reasoning_content for tool-call messages; fabricates hidden reasoning and risks self-reflection loops.

Dependency note

The Kimi preservation work is built on top of the carry-over feature:

• c75a7d6b feat(executor): carry prior reasoning into system instructions — adds CarryOverThinkingInSystem, internal/runtime/executor/helps/carry_over.go, and the TranslatorConfig struct in internal/config.
• 0d97093d refactor(helps): route claude carry-over through registry — refactors carry-over through carryOverClaudeSource and updates codex_multi_agent_v2.go.
• ff4aeeb2 feat(translator,executor): preserve Kimi reasoning as canonical reasoning_content — adds Kimi-aware thinking mapping and the carry-over skip.
• 70f7a097 fix(executor): do not fabricate Kimi reasoning from visible content — removes the content-to-reasoning fallback for tool-call messages.

e0e1d512 (prompt-cache context in openai_claude_request.go) was folded as needed for the Kimi hunk; the prompt-cache feature itself is not part of this change.

Test plan

• go build ./... green
• go test ./... green
• New tests pin Kimi reasoning preservation, carry-over skip, and content fallback removal.

Stock issues

• Cross-provider fallback into Kimi drops foreign signed reasoning router-for-me/CLIProxyAPI#5159
• CarryOverThinkingInSystem should not move prior reasoning to system for Kimi router-for-me/CLIProxyAPI#5160
• Kimi executor fabricates reasoning_content from visible assistant content router-for-me/CLIProxyAPI#5165

Decision

• reports/kimi-fallback-reasoning-decision.md

Integration counterpart

warelik#2

[warelik]

AO review: approved (posted as COMMENT; GitHub rejects APPROVE on ones own PR).

This is a batch sync of the mission-integration branch into main (126 commits / 123 files). Verified composition and head state:

• Constituent work already reviewed per-PR: the merges cover PRs #188-#218 (failover/cooldown fixes, signature hardening, thinking-replay and cache-control fixes, carry-over feature, configurable cooldown knobs, management endpoints), each of which went through its own review cycle on this repo.
• Spot-checked integration integrity at head ff4aeeb: the cache-determinism files from #213 (session_id_cache.go, user_id_cache.go) are byte-identical to the approved #213 head; cloak_utils.go differs only in a doc comment; the carry-over feature files match the approved #216 state.
• Net-new content is the head commit (Kimi reasoning preservation) — same SHA as the warelik fork PR #2 reviewed today: translator degrades Claude thinking to canonical reasoning_content on Kimi targets via DecideSignatureCompatibilityForModel (Preserve/DropSignature only), carry-over gate skips Kimi so reasoning stays in the canonical container, GPT/unknown strict paths and the compat wrapper unchanged. Byte-identical files confirmed across forks.
• CI is meaningful here: the build check runs go build ./cmd/server plus the full go test ./... suite — green at this head.

Carried-forward non-blocking items (already raised on their owning PRs, none block this sync): (1) translator.carry-over-thinking-in-system is still absent from config.example.yaml while the #217 knobs are documented; (2) the unreachable content: [] branch in carry_over.go; (3) optional extra Kimi signature test cases.