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, 6 insertions, 0 deletions

diff --git a/src/mcp/tools/common/history.h b/src/mcp/tools/common/history.h
index d6f5708..3b23027 100644
--- a/src/mcp/tools/common/history.h
+++ b/src/mcp/tools/common/history.h
@@ -5,6 +5,12 @@
 
 typedef struct tiny_history_index tiny_history_index_t;
 
+typedef struct tiny_history_index_session_info
+{
+  const char *session_id;
+  int64_t last_message_at;
+} tiny_history_index_session_info_t;
+
 tiny_history_index_t *tiny_history_index_build(const tiny_store_t *store);
 void tiny_history_index_free(tiny_history_index_t *index);
 bool