Stable Asura series IDs: strip rotating build hash (#6)

Asura series slugs carry a site-wide build hash (-059befe1) that rotates on every redeploy, silently orphaning all asura bookmarks (old-hash URLs 302 to new-hash ones, so detect() yields keys that never match stored rows).

Backend:
- migrateAsuraKeys in OpenStore: one-off idempotent migration rewriting hashed asura keys to the stable hashless ID, merging collisions to newest updated_at; losers deleted before winner rewrite (PK-collision safe) — regression tests included
- poller latestChapterFrom: build hash made optional in chapter-scoping regex so latest_chapter survives redeploys

Userscript:
- stripBuildHash(/-[0-9a-f]{8}$/) applied to seriesId in both asura detect branches; URLs keep full slug (stale hashes 302)
- load-time migration rewrites cached + retry-queued asura keys to the stripped form so a queued PUT cannot resurrect an orphaned row

Docs: AGENTS.md + CLAUDE.md URL-shape notes; design spec at docs/superpowers/specs/2026-07-28-asura-stable-series-id-design.md

Verified: go test -count=1 ./... green (new rotation + collision tests), node --check green, regex verified against live asurascans.com slugs.

Deploy order: backend first (migration runs at OpenStore). Orphan rows created by not-yet-updated userscripts self-heal on next backend restart.

Reviewed-on: #6
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/store.go

@@ -4,6 +4,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"regexp"
 	"strings"
 
 	_ "modernc.org/sqlite"
@@ -120,6 +121,10 @@ func OpenStore(path string) (*Store, error) {
 		db.Close()
 		return nil, fmt.Errorf("migrate schema: %w", err)
 	}
+	if err := migrateAsuraKeys(db); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("migrate asura keys: %w", err)
+	}
 	return &Store{db: db}, nil
 }
 
@@ -141,6 +146,73 @@ func migrateColumns(db *sql.DB) error {
 	return nil
 }
 
+// asuraBuildHash matches the trailing "-xxxxxxxx" site-wide build ID Asura
+// appends to every series slug. It rotates on each site redeploy, so it
+// must not be part of series_id. Must stay in sync with stripBuildHash in
+// userscript/manga-bookmark.user.js.
+var asuraBuildHash = regexp.MustCompile(`-[0-9a-f]{8}$`)
+
+// migrateAsuraKeys rewrites asura bookmarks whose series_id still carries
+// the build hash to the stable, hashless ID. Rows keyed with a hash are
+// orphaned on every Asura redeploy (old-hash URLs 302 to new-hash ones, so
+// detection yields a key that never matches). When two hash-generations of
+// one series collide, the row with the newest updated_at wins and the rest
+// are deleted. Idempotent: hashless IDs never match the regex.
+func migrateAsuraKeys(db *sql.DB) error {
+	rows, err := db.Query(`SELECT key, series_id, updated_at FROM bookmarks WHERE site = 'asura'`)
+	if err != nil {
+		return fmt.Errorf("list asura rows: %w", err)
+	}
+	type row struct {
+		key, id string
+		updated int64
+	}
+	var all []row
+	for rows.Next() {
+		var r row
+		if err := rows.Scan(&r.key, &r.id, &r.updated); err != nil {
+			rows.Close()
+			return fmt.Errorf("scan asura row: %w", err)
+		}
+		all = append(all, r)
+	}
+	if err := rows.Close(); err != nil {
+		return err
+	}
+
+	groups := map[string][]row{}
+	for _, r := range all {
+		stripped := asuraBuildHash.ReplaceAllString(r.id, "")
+		groups[stripped] = append(groups[stripped], r)
+	}
+	for stripped, g := range groups {
+		winner := 0
+		for i := range g {
+			if g[i].updated > g[winner].updated {
+				winner = i
+			}
+		}
+		// Losers go first: rewriting the winner to the stripped key while a
+		// pre-existing hashless row still holds it is a primary-key collision.
+		for i, r := range g {
+			if i == winner {
+				continue
+			}
+			if _, err := db.Exec(`DELETE FROM bookmarks WHERE key = ?`, r.key); err != nil {
+				return fmt.Errorf("drop duplicate %q: %w", r.key, err)
+			}
+		}
+		if r := g[winner]; r.id != stripped {
+			if _, err := db.Exec(
+				`UPDATE bookmarks SET key = ?, series_id = ? WHERE key = ?`,
+				"asura:"+stripped, stripped, r.key); err != nil {
+				return fmt.Errorf("rewrite key %q: %w", r.key, err)
+			}
+		}
+	}
+	return nil
+}
+
 func existingColumns(db *sql.DB, table string) (map[string]struct{}, error) {
 	rows, err := db.Query(`SELECT name FROM pragma_table_info(?)`, table)
 	if err != nil {