Give every blog its own Postgres database

A blog is now a database of its own (blog_<sub>) on the same server: one
pg_dump is a complete backup of a blog, one psql restores it, and nothing a
blog's queries do can reach another blog's rows. The control database
(DATABASE_URL) keeps only users and the blog registry (id, owner, subdomain,
db_name); title, tagline and theme move into a one-row settings table next
to the content so the dump really is everything.

db.Cluster holds the control pool plus small, lazily opened per-blog pools.
store.Store (control) hands out a store.BlogStore per blog; every blog_id
parameter and column is gone, the database is the scope. Handlers reach it
through blogStore(r), which resolveBlog puts in the context next to the blog.

Existing data is moved in place by control migration 00006, a Go migration
that runs inside the control transaction: it creates and migrates each blog
database, copies the rows preserving ids, and marks the registry; 00007 then
drops the old tables. Either every blog is moved or the control database is
untouched.

/media/{id} now serves the host's blog only, so dashboard previews on the
root domain use /b/{sub}/media/{id}. Subdomains are capped at 58 chars so
"blog_" + name fits a Postgres identifier. Deleting a user drops their
database. Store.Open resets a blog's pool and retries once so a database
restored under a running app (dropdb --force, createdb, psql) just works.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sd8UPWrvyYCLj97JexNw3A

1 files changed, 56 insertions, 0 deletions

diff --git a/internal/db/migrations/control/00003_layout.sql b/internal/db/migrations/control/00003_layout.sql
new file mode 100644
index 0000000..e8fff23
--- /dev/null
+++ b/internal/db/migrations/control/00003_layout.sql
@@ -0,0 +1,56 @@
+-- +goose Up
+-- Layout modules: what each area of a blog (header, columns, footer) shows.
+CREATE TABLE modules (
+    id          bigserial PRIMARY KEY,
+    blog_id     bigint NOT NULL REFERENCES blogs(id) ON DELETE CASCADE,
+    area        text NOT NULL CHECK (area IN ('header', 'left', 'right', 'above', 'below', 'footer')),
+    kind        text NOT NULL CHECK (kind IN ('title', 'logo', 'menu', 'archive', 'recent', 'html', 'rss', 'text', 'sitemap')),
+    title       text NOT NULL DEFAULT '',
+    body        text NOT NULL DEFAULT '',
+    count       integer NOT NULL DEFAULT 5,
+    sort_order  integer NOT NULL DEFAULT 0,
+    created_at  timestamptz NOT NULL DEFAULT now(),
+    updated_at  timestamptz NOT NULL DEFAULT now()
+);
+CREATE INDEX modules_blog ON modules (blog_id, area, sort_order, id);
+
+-- The menu: blog pages and custom links in one ordered list.
+CREATE TABLE menu_items (
+    id          bigserial PRIMARY KEY,
+    blog_id     bigint NOT NULL REFERENCES blogs(id) ON DELETE CASCADE,
+    page_id     bigint REFERENCES pages(id) ON DELETE CASCADE,
+    label       text NOT NULL DEFAULT '',
+    url         text NOT NULL DEFAULT '',
+    sort_order  integer NOT NULL DEFAULT 0,
+    CHECK (page_id IS NOT NULL OR url <> '')
+);
+CREATE UNIQUE INDEX menu_items_page ON menu_items (page_id) WHERE page_id IS NOT NULL;
+CREATE INDEX menu_items_blog ON menu_items (blog_id, sort_order, id);
+
+-- Existing blogs keep the menu they had: pages marked "show in menu", in menu
+-- order, with the home page only if the theme included it.
+INSERT INTO menu_items (blog_id, page_id, sort_order)
+SELECT p.blog_id, p.id, row_number() OVER (PARTITION BY p.blog_id ORDER BY p.nav_order, p.id) - 1
+FROM pages p JOIN blogs b ON b.id = p.blog_id
+WHERE p.show_in_nav AND (NOT p.is_home OR coalesce((b.theme->>'nav_show_home')::boolean, true));
+ALTER TABLE pages DROP COLUMN show_in_nav;
+
+-- ...and the layout their theme described.
+INSERT INTO modules (blog_id, area, kind, sort_order)
+SELECT id, 'header', 'title', CASE WHEN theme->>'nav_position' = 'top-bar' THEN 1 ELSE 0 END
+FROM blogs WHERE coalesce((theme->>'header_show_title')::boolean, true);
+INSERT INTO modules (blog_id, area, kind, sort_order)
+SELECT id, 'header', 'menu', CASE WHEN theme->>'nav_position' = 'top-bar' THEN 0 ELSE 1 END
+FROM blogs WHERE coalesce(theme->>'nav_position', 'below-header') <> 'left-sidebar';
+INSERT INTO modules (blog_id, area, kind, sort_order)
+SELECT id, 'left', 'menu', 0 FROM blogs WHERE theme->>'nav_position' = 'left-sidebar';
+INSERT INTO modules (blog_id, area, kind, body, sort_order)
+SELECT id, 'footer', 'text', theme->>'footer_text', 0 FROM blogs WHERE coalesce(theme->>'footer_text', '') <> '';
+INSERT INTO modules (blog_id, area, kind, sort_order)
+SELECT id, 'footer', 'rss', 1 FROM blogs WHERE coalesce((theme->>'footer_show_rss')::boolean, true);
+
+-- +goose Down
+ALTER TABLE pages ADD COLUMN show_in_nav boolean NOT NULL DEFAULT true;
+UPDATE pages SET show_in_nav = EXISTS (SELECT 1 FROM menu_items m WHERE m.page_id = pages.id);
+DROP TABLE menu_items;
+DROP TABLE modules;