search: cache results

docs/api/rest.md

@@ -294,8 +294,14 @@ Behavior notes:
 - Response: `{ "searches": SearchSummary[] }`
 
 ### `POST /v1/searches`
-- Body: `{ "title"?: string, "query"?: string }`
-- Response: `{ "search": SearchSummary }`
+- Body: `{ "title"?: string, "query"?: string, "reuseByQuery"?: boolean }`
+- Response: `{ "search": SearchSummary, "reused": boolean, "cacheHit": boolean }`
+
+Behavior notes:
+- `reuseByQuery` defaults to `false`, preserving the normal create-a-new-search behavior.
+- When `reuseByQuery` is `true` and `query` is present, the backend normalizes the query with `trim().toLowerCase()` and returns the most recently updated existing search with that normalized query instead of creating a duplicate.
+- `cacheHit` is `true` only when the reused search has persisted results or answer text, is not currently streaming, and was updated within the 24-hour search cache window. Clients can then fetch `GET /v1/searches/:searchId` and display it without running another search.
+- If a matching search exists but `cacheHit` is `false`, clients may run the search again on the returned `search.id`; the run endpoints replace that search's persisted results and answer with the latest run.
 
 ### `PATCH /v1/searches/:searchId/star`
 - Body: `{ "starred": boolean }`