Merge pull request 'fix: series removal sent its status line twice' (#176) from fix/series-remove-double-writeheader into main

adminSeriesRemove answered the list surface with two h.render calls -- the
row fragment and the out-of-band heading -- and h.render writes a status
line each time, so every removal logged "superfluous
response.WriteHeader call". The heading is an append to a response
already committed, so it now executes straight onto w, the way
writeChromeOOB already does it.

The regression test runs the router under a real server with a captured
ErrorLog: a ResponseRecorder never sees this warning, which is why the
existing removal test did not catch it.

AGENTS.md

@@ -50,6 +50,15 @@ Backend (`cd backend`):
 
 Local stack: `docker compose up` (bookmark-api + postgres only; `postgres-data` named volume, `restart: unless-stopped`). No browser — without `BROWSER_WS_URL` the poller logs and skips kagane and comix. To run one: `cd chrome && BROWSER_BIND_ADDR=172.17.0.1 docker compose up -d --build`, then `BROWSER_WS_URL=ws://172.17.0.1:9222` in the root `.env` (bridge gateway, so the API container can name it by IP).
 
+**Clean up Docker after testing.** Storage on the dev machine is scarce, so
+anything you started for a test you also tear down before calling the work
+done: `docker compose down -v` for a stack you brought up, `docker rm -f -v`
+for a container you ran by hand (`-v`, or the image's anonymous data volume
+survives). Then check `docker volume ls` and `docker system df` for leftovers
+and reclaim them — a dangling volume nobody notices is the leak that fills the
+disk. Never remove the `postgres-data` volume of a stack the user is actually
+running, and never blanket-`docker system prune` their images or build cache.
+
 Live CDP proof (needs that browser and network, skipped otherwise):
 `SMOKE_BROWSER_WS_URL=ws://<ip>:<port> go test -run 'TestSmokeKagane|TestSmokeComix' ./internal/latest`
 — fetches a real kagane and comix cover and chapter list. A red run means the challenge is

backend/internal/pgtest/pgtest.go

@@ -40,7 +40,9 @@ func Main(m *testing.M) int {
 		fmt.Println("pgtest:", err)
 		return 1
 	}
-	defer exec.Command("docker", "rm", "-f", id).Run()
+	// -v: the postgres image declares a VOLUME, so an explicit rm without it
+	// leaves the anonymous data volume behind on every test run.
+	defer exec.Command("docker", "rm", "-f", "-v", id).Run()
 
 	adminURL = url
 	return m.Run()
@@ -85,7 +87,7 @@ func start() (id, url string, err error) {
 
 	port, err := exec.Command("docker", "port", id, "5432/tcp").Output()
 	if err != nil {
-		exec.Command("docker", "rm", "-f", id).Run()
+		exec.Command("docker", "rm", "-f", "-v", id).Run()
 		return "", "", fmt.Errorf("docker port: %w", err)
 	}
 	// "0.0.0.0:32768" (and possibly a second, IPv6 line); the port is all we want.
@@ -94,7 +96,7 @@ func start() (id, url string, err error) {
 		first[strings.LastIndex(first, ":")+1:])
 
 	if err := waitReady(url); err != nil {
-		exec.Command("docker", "rm", "-f", id).Run()
+		exec.Command("docker", "rm", "-f", "-v", id).Run()
 		return "", "", err
 	}
 	return id, url, nil

backend/internal/web/admin_series.go

@@ -505,10 +505,13 @@ func (h *Handler) adminSeriesRemove(w http.ResponseWriter, r *http.Request) {
 		band = 1
 	}
 	h.render(w, http.StatusOK, "series-row", seriesRow(a, band, time.Now()))
+	// The heading is an out-of-band append to a response whose status line has
+	// already gone out with the row, so it is executed straight onto w —
+	// h.render would send a second WriteHeader.
 	if head, err := h.seriesListHeadView(r); err != nil {
 		log.Printf("series remove %s: %v", site+":"+seriesID, err)
-	} else {
+	} else if err := h.tmpl.ExecuteTemplate(w, "series-list-head", head); err != nil {
-		h.render(w, http.StatusOK, "series-list-head", head)
+		log.Printf("series remove %s: render series-list-head oob: %v", site+":"+seriesID, err)
 	}
 }
 

backend/web_test.go

@@ -1,11 +1,13 @@
 package main
 
 import (
+	"bytes"
 	"crypto/sha256"
 	"database/sql"
 	"encoding/json"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
@@ -4285,6 +4287,52 @@ func TestRemoveFromListAnswersRowAndFreshHeading(t *testing.T) {
 	}
 }
 
+// The removal answers two fragments on one response. The second is an
+// out-of-band append, so it must not send a second status line: net/http
+// answers a double WriteHeader with "superfluous response.WriteHeader call"
+// on the server's error log, which a ResponseRecorder never sees. Hence a
+// real server here.
+func TestRemoveFromListSendsOneStatusLine(t *testing.T) {
+	st, dsn := newTestStoreURL(t)
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatalf("open %s: %v", dsn, err)
+	}
+	defer db.Close()
+	seedSeriesRow(t, st, db, seriesRowSeed{key: "asura:a", url: "u", checkedAt: 9000, bookmarks: 0})
+
+	var errLog bytes.Buffer
+	srv := httptest.NewUnstartedServer(newRouter(st, testConfig()))
+	srv.Config.ErrorLog = log.New(&errLog, "", 0)
+	srv.Start()
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodPost, srv.URL+"/admin/series/asura:a/remove",
+		strings.NewReader("filter=no_readers&band=0"))
+	if err != nil {
+		t.Fatalf("build request: %v", err)
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.AddCookie(sessionCookie(t, st))
+	resp, err := srv.Client().Do(req)
+	if err != nil {
+		t.Fatalf("removal request: %v", err)
+	}
+	body, _ := io.ReadAll(resp.Body)
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("removal status = %d, want 200", resp.StatusCode)
+	}
+	// Both fragments still travel: the fix must not have dropped the heading.
+	if !strings.Contains(string(body), "Title of asura:a") ||
+		!strings.Contains(string(body), `hx-swap-oob="true"`) {
+		t.Errorf("answer lost a fragment:\n%s", body)
+	}
+	if strings.Contains(errLog.String(), "superfluous") {
+		t.Errorf("removal wrote the status line twice: %s", errLog.String())
+	}
+}
+
 // A removal from the detail page navigates to the No-Readers list: htmx gets
 // a full navigation (HX-Redirect — a 303 would be followed by the request
 // and the list page swapped into the press's target), plain clients the 303