Improve agent-facing history endpoints (Phase 1)

- Fix /api/history/{type} to search the full persistent store instead of
  only the bounded in-memory ring buffer, so filtered history isn't
  silently truncated.
- Add structured type/since/until filters to /api/history/search and
  /api/history/wait, alongside the existing free-text query.
- Add GET /api/traces/{traceId} to fetch all entries for a trace in one
  call instead of relying on substring search.
- Rate-limit /api/history/wait per client IP.
- Add docs/PLAN.md tracking the phased improvement plan; update README
  and agents_example.md for the new/changed endpoints.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/storage/file_store_test.go

@@ -50,7 +50,7 @@ func TestFileStore(t *testing.T) {
 	}
 
 	// Test Search
-	results, err := fs.Search(ctx, "hello", 10)
+	results, err := fs.Search(ctx, SearchOptions{Query: "hello"}, 10)
 	if err != nil {
 		t.Fatalf("Search failed: %v", err)
 	}
@@ -64,3 +64,56 @@ func TestFileStore(t *testing.T) {
         t.Errorf("unexpected data content: %s", string(data))
     }
 }
+
+func TestFileStoreSearchFilters(t *testing.T) {
+	filename := "test-otel-filters.log"
+	defer func() {
+		_ = os.Remove(filename)
+	}()
+
+	fs := NewFileStore(filename)
+	ctx := context.Background()
+
+	entries := []websocket.HistoryEntry{
+		{Type: "logs", Timestamp: 100, Data: json.RawMessage(`{"msg":"first log"}`)},
+		{Type: "traces", Timestamp: 200, Data: json.RawMessage(`{"msg":"a trace"}`)},
+		{Type: "logs", Timestamp: 300, Data: json.RawMessage(`{"msg":"second log"}`)},
+	}
+	for _, e := range entries {
+		if err := fs.Append(ctx, e); err != nil {
+			t.Fatalf("failed to append entry: %v", err)
+		}
+	}
+
+	// Filter by type only
+	results, err := fs.Search(ctx, SearchOptions{Type: "logs"}, 10)
+	if err != nil {
+		t.Fatalf("Search failed: %v", err)
+	}
+	if len(results) != 2 {
+		t.Fatalf("expected 2 log entries, got %d", len(results))
+	}
+	for _, r := range results {
+		if r.Type != "logs" {
+			t.Errorf("expected type 'logs', got %s", r.Type)
+		}
+	}
+
+	// Filter by time range: only the entry at Timestamp=200 should match
+	results, err = fs.Search(ctx, SearchOptions{Since: 150, Until: 250}, 10)
+	if err != nil {
+		t.Fatalf("Search failed: %v", err)
+	}
+	if len(results) != 1 || results[0].Timestamp != 200 {
+		t.Fatalf("expected single entry at timestamp 200, got %+v", results)
+	}
+
+	// Combine type and query filters
+	results, err = fs.Search(ctx, SearchOptions{Type: "logs", Query: "second"}, 10)
+	if err != nil {
+		t.Fatalf("Search failed: %v", err)
+	}
+	if len(results) != 1 || results[0].Timestamp != 300 {
+		t.Fatalf("expected single entry at timestamp 300, got %+v", results)
+	}
+}