docs(rfc): introduce atomic memory as independent artifacts

[frf12]

Which issue or RFC does this PR close?

RFC #1809 proposal; no issue is closed by this documentation PR.

Depends on #1803 for the common search contract and #1771 for offline migration. Amends RFCs 0014, 0019, 1345, 1652, and 1718; related contracts include RFCs 1417 and 1549.

Rationale for this change

Legacy Memory versions a Scope-level collection containing a full manifest of entry-version references. Changing one entry stores another complete manifest and updates the shared collection head. Built-in extraction supplies all active entries to the model as memories accumulate.

Independent memory Artifacts align identity and history with Scope. Retrieval before reconciliation reduces unrelated model input, while explicit merge and restoration behavior lets users correct automatic decisions.

What changes are included in this PR?

• English and Chinese RFCs for the atomic-memory Family: one independently maintained memory per Artifact, with its own identity, revisions, evidence, and state.
• Candidate generation followed by retrieval of related active memories in the same Scope that the processing identity may both read and write. All results meeting the relevance threshold enter comparison; batching does not impose a fixed total cutoff. Deployments without vector search still retrieve related memories.
• Automatic creation, revision, and merging without per-operation approval or category preauthorization. The proposal explicitly changes RFC 1652's merge approval requirement for Atomic Memory.
• Merges create a new Artifact and freeze the inputs. Four states distinguish active, forgotten, merged, and retired memories.
• Content correction, historical revision restoration, and merge undo have distinct effects. One request can restore a merged input through successive merges; retired results remain readable but cannot be reactivated.
• Separate restoration preview and execution, with optional preview checks. Direct callers need no preview, while permission, current-state, and concurrency checks always apply.
• Search follows docs(rfc): define artifact search projections and join-free retrieval #1803. Offline migration follows docs(rfc): define unified versioned database migrations #1771, with compatibility adapters for supported old API contracts and explicit release arrangements for deprecation and cleanup.
• Open questions cover correction context captured by Agent integrations and adoption of the four states by other Artifact families.

Are there any user-facing changes?

Documentation only. The proposal describes a future breaking change to Memory identities and storage, with an offline upgrade. Compatible old memory APIs adapt requests and responses to the new Family while retaining their contract. Incompatible operations require declared replacements and deprecation/removal arrangements under #1771.

The RFC specifies behavior, compatibility, and tradeoffs. Table schemas, SQL, API parameters, and locking implementation remain in the separate implementation design.

How was this change tested?

• Checked relative Markdown links, the nine RFC sections, literal UTF-8 text, and whitespace.
• Reviewed English and Chinese content for consistency with the agreed behavior.
• git diff --cached --check and repository commit hooks.
• Verified that the PR contains one commit and only the two RFC documents.

No application tests or database benchmarks were run for this documentation-only change.

AI usage statement

Prepared with OpenAI Codex (GPT-6), including document drafting and source-grounded review, under maintainer direction.

[AlexStocks]

[P2] 声明取消 RFC 1345 的约束，但未覆盖 1345 明确要求承接 RFC 定义的项

此处写「removes RFC 1345's requirement for one active Memory collection per Scope」。1345 的原文是「One Scope has one active Memory progression line」（docs/en/rfcs/1345_scope_organization_and_agent_integration.md:469），且位于 Future work 的「Several Memory Artifacts in one Scope」一节；该节紧接着规定：「A later RFC supporting several Memory progression lines in one Scope must define a stable Memory binding, Source assignment, per-Memory cursors, Prepare Context selection, and concurrency conflicts」（1345:474-475）。

本 RFC 正是那个承接者。已覆盖 Source assignment（「the Scope's extraction flow still owns processing progress」）与并发（「Search and concurrency」一节），但全文（英文版与中文版均）没有出现 Prepare Context / cursor / recall 任何一词。多记忆 Artifact 之后，「Prepare Context 注入哪些记忆、按什么边界截断」恰是 1345 点名要定义的项之一。

建议：在「Search and concurrency」或「Unresolved questions」显式写出对该项的处置（即使结论是「由 #1803 的检索契约覆盖」也应写明）；并考虑把「Memory collection」与 1345 的「Memory progression line」用语对齐，否则读者对照原文会找不到依据。中文版此处表述一致（docs/zh/rfcs/1809-atomic-memory.md:135-136），需同步修改。