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, 13 insertions, 1 deletions

diff --git a/src/domain/search.h b/src/domain/search.h
index 3408998..a891a27 100644
--- a/src/domain/search.h
+++ b/src/domain/search.h
@@ -15,8 +15,20 @@ bool tiny_search_index_add(tiny_search_index_t *index,
                            size_t message_index);
 bool tiny_search_index_candidates(const tiny_search_index_t *index,
                                   const char *query,
-                                  size_t **message_indices,
+                                  size_t **output,
                                   size_t *count);
+
+typedef struct tiny_search_breakdown
+{
+  double total;
+  double content;
+  double summary;
+  double tags;
+} tiny_search_breakdown_t;
+
 double tiny_search_score(const char *query, const tiny_message_t *message);
+bool tiny_search_score_breakdown(const char *query,
+                                 const tiny_message_t *message,
+                                 tiny_search_breakdown_t *breakdown);
 
 #endif