store: keep what she read out of what he said

Nothing at read time told a feed item or a crawled page apart from his own
notes. QueryNotes ranked every note by cosine and the notes answer handed the
nearest five to the phraser, so "что я говорил про переезд" could be answered
out of a stranger's web page, prefixed with "вот что я нашла: ". Recall now
excludes the read sources, rss: and crawl:, and the list is one place.

The feed answer needed a different read as a result, and it needed one anyway:
it scanned the last 200 notes of any source, so a busy day of voice notes pushed
the newest headline out of the window and she said "в лентах пока ничего
нового" while the poller was working fine. RecentNotesFromSource asks for feed
notes by source, so the window holds 200 of them.

Found in review of #66 and #67.

internal/ipc/api.go

@@ -454,6 +454,10 @@ type outcomesReq struct {
 type nReq struct {
 	N int `json:"n"`
 }
+type sourceNReq struct {
+	Prefix string `json:"prefix"`
+	N      int    `json:"n"`
+}
 type calendarEventsReq struct {
 	From time.Time `json:"from"`
 	To   time.Time `json:"to"`
@@ -606,6 +610,11 @@ type CoreAPI interface {
 	WriteNote(ctx context.Context, ts time.Time, text string, embedding []float32, source string) (int64, error)
 	QueryNotes(ctx context.Context, embedding []float32, k int) ([]Note, error)
 	RecentNotes(ctx context.Context, n int) ([]Note, error)
+	// RecentNotesFromSource — the newest n notes whose source starts with
+	// prefix. Notes Maven read rather than heard (rss:, crawl:) are excluded
+	// from recall, so this is the only way to reach them, and it keeps the feed
+	// answer from being crowded out of a fixed window by his own notes.
+	RecentNotesFromSource(ctx context.Context, prefix string, n int) ([]Note, error)
 
 	// ProposeTool drafts an inert 'proposed' tool scaffold (maven-callable);
 	// returns whether a new proposal was written. EnableTool fills cmd +