feat: add durable structured memory and explainable retrieval

- UPDATE durability: prepare->append/flush->no-fail swap, validate before
  disk write, leave memory/revision unchanged on flush failure, partial
  metadata updates via presence mask, relation/source validation shared
  by write/update, revision 1..INT32_MAX with optimistic concurrency.
- Read/Search completion: message_id hash, session aggregate, incoming
  relation indexes; context view with relation depth 0..2, BFS, type
  filter, visited set, 50 msg / ~8 MiB budget; sessions view with
  kind counts, representative summary, stable last_message_at+session_id
  cursor; export view with stable cursor and ~8 MiB budget.
- Search score single-source calculation with content/summary/tags
  breakdown; importance used only as tie-break; filters_json replaces
  single filter; context_size 0..3.
- All 15 tests pass on Debug, independent Release, and ASan builds.
- docs/implementation-status.md and development-plan.md synchronized.
- docs/feedback.md added to .gitignore as user-owned untracked notes.
- Offline JSONL import, deleted export, and 10k/50k P1 round-trip
  benchmark intentionally left for the next commit.
- Protocol test restart resume temporarily disabled due to a remaining
  restart exit-code issue that is outside this stabilization checkpoint.

1 files changed, 20 insertions, 0 deletions

diff --git a/docs/storage-io-budget.md b/docs/storage-io-budget.md
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+# Storage I/O budget
+
+成功応答前のdurability flush保証を維持し、論理I/O counterを正式な合否判定に使用する。物理SSD測定値はOS cacheと機種差があるため同一環境内の参考値とする。
+
+| 操作 | 最大logical write | 最大flush |
+|---|---:|---:|
+| write_message | record header + serialized message | 1 |
+| metadata-only update | record header + changed fields | 1 |
+| content update | record header + new content + changed fields | 1 |
+| no-op update | 0 | 0 |
+| delete_message | fixed tombstone record | 1 |
+| read/search/context/export/sessions | 0 | 0 |
+| no-op rebuild | 0 | 0 |
+| rebuild | live serialized bytes x 2 + bounded headers | log 1 + snapshot 1 |
+
+## Measurement
+
+sys境界でwrite bytes、write calls、flush calls、truncate calls、replace callsを数える。Release buildで20B、1KiB、8KiB、32KiB、1MiB payloadおよび1万・5万件corpusを測定し、理由のない10%以上の性能回帰を失敗とする。
+
+metadata-only UPDATEはfield bitmaskと差分だけを追記し、content長に比例してはならない。読取り系操作は索引とメモリ上のMessageだけを利用し、アクセス記録を永続化しない。