feat(session): persist metadata + inject into memory extraction prompt (#2414)

[yeyitech]

Summary

Closes #2414. Today the only way to express project-level personalization (architectural style, tech-stack preferences) is to allocate a different agent_id per project. This PR ships the foundational piece — arbitrary session-level metadata that persists end-to-end and is injected into the memory extractor's prompt context — so a single agent can keep distinct memory layers across projects.

Surface

• Model + storage: Session.metadata: dict | None, JSON-serializable, capped at 16 KB / 64 keys (module constants, no config field).
• API:
  • POST /api/v1/sessions — accepts optional metadata on create.
  • GET /api/v1/sessions/{id} — includes metadata in the response.
  • PATCH /api/v1/sessions/{id}/metadata — merges by default; ?replace=true overwrites.
• Extractor: when metadata is present, a [Session metadata] block is added to the system prompt the LLM sees during memory extraction.
• CLI: ov session set-metadata <id> --key K --value V (repeatable).

Per-schema multi-layer memory (the issue's longer-term ask) is intentionally out of scope and lands as a follow-up — this PR just makes the foundation available.

Test plan

• pytest tests/server/test_session_metadata.py -x -q passes (7 cases).
• Manual: curl -X PATCH /api/v1/sessions/{id}/metadata -d '{\"project\":\"alpha\"}' then GET returns it; commit a session and verify the LLM extractor saw the metadata block.
• Existing session tests still pass.

Closes #2414

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PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🎫 Ticket compliance analysis 🔶 2414 - Partially compliant Compliant requirements: 服务端增加session metadata 额外字段持久保存 vlm抽取记忆时,将session metadata 加入到系统上下文 Non-compliant requirements: schema配合实现多层记忆抽取 (marked as out of scope)

⏱️ Estimated effort to review: 3 🔵🔵🔵⚪⚪

🏅 Score: 85

🧪 PR contains tests

🔒 No security concerns identified

✅ No TODO sections

🔀 Multiple PR themes Sub-PR theme: feat(session): core metadata support (persistence, API, extractor injection) Relevant files: openviking/server/routers/sessions.py openviking/service/session_service.py openviking/session/compressor_v2.py openviking/session/memory/session_extract_context_provider.py openviking/session/session.py openviking/session/session_metadata.py tests/server/test_session_metadata.py Sub-PR theme: feat(cli): add session set-metadata command Relevant files: crates/ov_cli/src/commands/session.rs crates/ov_cli/src/handlers.rs crates/ov_cli/src/main.rs

⚡ Recommended focus areas for review Invalid Default for Telemetry Field The telemetry field in CreateSessionRequest and UpdateMetadataRequest uses False as a default value, which is likely incompatible with the TelemetryRequest type. This will cause Pydantic validation errors for requests that don't explicitly provide telemetry data, breaking existing functionality. telemetry: TelemetryRequest = False class UpdateMetadataRequest(BaseModel): """Request model for updating session metadata.""" metadata: Dict[str, Any] = Field(default_factory=dict) telemetry: TelemetryRequest = False

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