fix: 对齐 langgraph-api 的 config/context 互斥与同步语义（runs + assistants）

[LiangMuYuan]

Summary

• config.configurable 与 context 同时非空时返回 400（对齐 langgraph-api 的互斥语义）
• 两者互相同步：传 context 时写回 config["configurable"]；只传 configurable 时推导为 context
• 图无 context_schema 时，context 不再被静默丢弃，而是通过 config["configurable"] 传递给图，老式节点（读 configurable）可读
• run 准备阶段（run_preparation.py）：assistant 的 config 也作为默认值合并进 run（此前只合并 context，存在 assistant.config.configurable 上的参数运行时读不到）
• assistant 创建/更新（api/assistants.py）：创建和 PATCH 时按 langgraph-api 语义镜像同步 config.configurable ↔ context（只传一个自动推导另一个；两个都传返回 400）
• 新增单元/集成测试：互斥校验、双向同步、context_schema 字段过滤、API 层 400、assistant 创建/更新镜像同步

修复方式

execute_run() 在注入内部 key（thread_id / checkpoint 等）之前，先按 langgraph-api 语义处理用户参数：

• config.configurable 与 context 均非空 → ValueError（api/runs.py 的 _validate_supported_run_controls 对 runs / stateless runs 直接返回 400）
• 仅传 context → 镜像到 config["configurable"]
• 仅传 configurable → 推导为 explicit_context，供 _resolve_run_context 过滤后传给图的 context 参数

_prepare_run()（run_preparation.py）把 assistant 的 config 与 context 都作为默认值合并进 run kwargs（assistant 为默认、请求覆盖，configurable 子层深合并）。

create_assistant / patch_assistant（api/assistants.py）通过 _consolidate_config_context() 镜像同步 config.configurable ↔ context，与 langgraph-api 的 ops 层约定一致。

Test Plan

• uv run pytest tests/unit/test_run_executor.py tests/unit/test_run_controls_validation.py -q（26 passed）
• uv run pytest tests/integration/test_runs_compat.py tests/integration/test_runs_streaming.py -q（33 passed）
• uv run pytest tests/integration/test_assistants_config_context_sync.py -q（7 passed）
• uv run pytest -q（789 passed, 24 skipped，WSL2 Ubuntu 24.04 全量通过）

Target Branch Check

• feature/* PRs target develop
• release/* PRs target main
• hotfix/* PRs target main

Closes #64

[webup]

Blocking issue at src/agentseek_api/api/assistants.py:148: if_exists="do_nothing" returns the existing assistant before _consolidate_config_context() runs. Reproduction: create a fixed assistant ID, then POST the same ID with if_exists="do_nothing", non-empty config.configurable, and non-empty context; the endpoint returns 200, while the locked langgraph-api 0.9.0 implementation validates the conflict first and returns 400. Please move the validation/consolidation before this early return and add a regression test for the idempotent-create retry path.

[LiangMuYuan]

Thanks for the review! This is fixed in 9e287a6.

create_assistant now runs _consolidate_config_context() before the if_exists=do_nothing early return, so the config/context mutual-exclusion check (both non-empty -> 400) is enforced even on idempotent-create retries, matching langgraph-api's consolidate_config_and_context ordering.

Added regression test test_create_do_nothing_retry_still_validates_config_context_conflict covering:

• retry with a conflicting config.configurable + context -> 400
• non-conflicting retry -> 200 and returns the existing assistant

Verified on Linux (WSL2): related assistant/config-context tests 57 passed, full tests/unit 531 passed.

[webup]

The original if_exists="do_nothing" validation blocker is fixed in 9e287a6, but one required follow-up remains on this exact head.

tests/e2e/test_langsmith_compat_live.py:156-157 still sends both a non-empty config.configurable and context. Under the new compatibility contract this correctly returns 400, while _create_assistant() still asserts 200. This currently fails all six MySQL/PostgreSQL database matrix jobs. Please send only one representation in this live test and verify the mirrored value in the response.

Separately, the four Docker/Redis jobs are failing because the generated image resolves mcp>=1.27.1 to mcp 2.0.0, where Server.list_tools() is no longer available. That is not introduced by this PR diff, but the exact-head checks still need a green rerun after it is addressed.

Local verification on 9e287a6: 788 passed, 5 skipped; coverage 90.61%; focused compatibility tests, Ruff, lockfile check, and diff check all pass.

[webup]

Resolved on exact head 973738b.

The live database-backed E2E now validates both context-to-config mirroring on create and config-to-context mirroring on patch without sending mutually exclusive inputs. The package also constrains the v1 MCP SDK to <2, so fresh/Docker installs no longer resolve the breaking 2.0 API.

Verification: local coverage suite 788 passed, 5 skipped (90.61%); fresh Python 3.12 install selected MCP 1.29.0 and initialized the low-level server API; exact-head GitHub Actions completed 18/18 checks successfully, including all MySQL/PostgreSQL matrices, Redis durable execution, and CLI Docker Runtime.

[webup]

Thanks @LiangMuYuan for the contribution and the quick follow-up on the config/context compatibility fixes. The final update passed the full CI matrix and has now been squash-merged.