Keep the empty host when the db_url path starts with //

defaultDBURL kept the empty host only when state_dir started with //,
but SQLite reads the path written into the URL, state_dir followed by
/state.sqlite3. For a state_dir of / that path is //state.sqlite3, the
URL started file:// and SQLite read state.sqlite3 as a host, so pixa
failed to start. The decision now looks at that path: a state_dir of
/ gives file:////state.sqlite3. Every other state_dir gives the same
URL as before.

Model: opus-5-5

README.md

@@ -726,13 +726,13 @@ Key settings in more detail:
 - `db_url` — the SQLite database to open; omitted, it is
   `file:<state_dir>/state.sqlite3?_pragma=journal_mode(WAL)`, which keeps the
   database in WAL mode. `state_dir` is percent-encoded in it, so a `%`, `?` or
-  `#` in the name is written as `%25`, `%3F` or `%23`. For a `state_dir`
-  starting with `//` it starts `file:////`, so SQLite does not read the first
-  directory name as a host. pixa opens one connection to it, so its own reads
-  and writes run one at a time. pixa adds `_pragma=busy_timeout(5000)` to any
-  `db_url`, so a write that finds another program writing to the file waits up
-  to five seconds for it instead of failing. WAL mode comes only from the URL:
-  keep `_pragma=journal_mode(WAL)` in one you set
+  `#` in the name is written as `%25`, `%3F` or `%23`. For a `state_dir` of `/`
+  or one starting with `//` it starts `file:////`, so SQLite does not read the
+  first name in the path as a host. pixa opens one connection to it, so its own
+  reads and writes run one at a time. pixa adds `_pragma=busy_timeout(5000)` to
+  any `db_url`, so a write that finds another program writing to the file waits
+  up to five seconds for it instead of failing. WAL mode comes only from the
+  URL: keep `_pragma=journal_mode(WAL)` in one you set
 - `cache_max_bytes` — disk cache size limit in bytes; `0` disables the disk
   cache entirely; omitted defaults to 75% of the sum of the free space on the
   filesystem containing `<state_dir>/cache/` and the bytes of source and

TODO.md

@@ -30,6 +30,14 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
+- 2026-10-16 a `state_dir` whose name holds `%`, `?` or `#` keeps its database
+  at `state.sqlite3` in that directory (closes #290): the `db_url` derived from
+  it put the name into a `file:` URL as it was, so SQLite read `%41` as `A`, a
+  `?` or `#` ended the path early, and the journal mode parameter was lost. The
+  derived `db_url` is now built with Go's `net/url`, which writes those
+  characters as `%25`, `%3F` and `%23`. For a `state_dir` of `/` or one starting
+  with `//` it starts `file:////`, so SQLite no longer reads the first name in
+  the path as a host.
 - 2026-10-16 a size with one side `0` keeps the side computed from the source's
   proportions at 1 or more (closes #283): it was rounded down, so for a thin
   source it came out at 0, and libvips then made the size square. An 8192x1
@@ -62,14 +70,6 @@ P2: security: per-origin rate limiting
   another way, such as with `%2F` in the path, whatever else the path holds, or
   with a user name and password. It also answers 400 for a source path holding a
   `..` segment, as `/v1/image/` refuses one.
-- 2026-10-16 a `state_dir` whose name holds `%`, `?` or `#` keeps its database
-  at `state.sqlite3` in that directory (closes #290): the `db_url` derived from
-  it put the name into a `file:` URL as it was, so SQLite read `%41` as `A`, a
-  `?` or `#` ended the path early, and the journal mode parameter was lost. The
-  derived `db_url` is now built with Go's `net/url`, which writes those
-  characters as `%25`, `%3F` and `%23`. For a `state_dir` starting with `//` it
-  starts `file:////`, so SQLite no longer reads the first directory name as a
-  host.
 - 2026-10-15 a thin source requested with `fit=cover` no longer makes libvips
   build a huge image (closes #282): libvips' thumbnail scaled the whole source
   to cover the requested size and copied that into memory before it cut out the

internal/config/config.go

@@ -359,14 +359,18 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 // the directory name, which SQLite decodes back, so the URL names exactly
 // this file. OmitHost writes file:/var/lib/pixa/... instead of
 // file:///var/lib/pixa/..., and keeps a relative stateDir from being read
-// as a host name. A stateDir starting with // keeps the empty host, so the
-// URL starts file://// and SQLite does not read the first directory name
-// as a host.
+// as a host name. The path written into the URL is stateDir followed by
+// /state.sqlite3; when it starts with //, as it does for a stateDir of /
+// or one starting with //, the empty host is kept, so the URL starts
+// file://// and SQLite does not read the first name in the path as a
+// host.
 func defaultDBURL(stateDir string) string {
+	dbPath := stateDir + "/state.sqlite3"
+
 	dbURL := url.URL{
 		Scheme:   "file",
-		OmitHost: !strings.HasPrefix(stateDir, "//"),
-		Path:     stateDir + "/state.sqlite3",
+		OmitHost: !strings.HasPrefix(dbPath, "//"),
+		Path:     dbPath,
 		RawQuery: "_pragma=journal_mode(WAL)",
 	}