feat: PostgreSQL driver support

features/postgres_database_driver.feature

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+Feature: Optional PostgreSQL database driver
+  An operator who prefers PostgreSQL runs RenewCMS against it by setting
+  environment variables. SQLite stays the default, and MySQL/MariaDB behaves
+  exactly as before.
+
+  Background:
+    Given the database drivers are registered by name in database.drivers
+    And the database is chosen by the DB_DRIVER environment variable
+    And repositories, use cases and handlers are unchanged
+
+  Scenario Outline: Driver selection
+    Given DB_DRIVER is "<value>"
+    When the server starts
+    Then the outcome is "<outcome>"
+
+    Examples:
+      | value      | outcome                                                  |
+      | unset      | the sqlite driver opens DB_FILE                          |
+      | sqlite     | the sqlite driver opens DB_FILE                          |
+      | mysql      | the mysql driver opens the DB_HOST connection            |
+      | postgres   | the postgres driver opens the DB_HOST connection         |
+      | postgresql | the postgres driver opens the DB_HOST connection         |
+      | oracle     | startup fails with: unsupported database driver "oracle" |
+
+  Scenario Outline: Missing PostgreSQL variable
+    Given DB_DRIVER is "postgres"
+    And "<missing>" is not set
+    When the environment is validated
+    Then startup fails with "Environment variable <missing> is not set"
+
+    Examples:
+      | missing     |
+      | DB_HOST     |
+      | DB_USER     |
+      | DB_PASSWORD |
+      | DB_NAME     |
+
+  Scenario: SQLite and MySQL do not require PostgreSQL-only variables
+    Given DB_DRIVER is "sqlite" or "mysql"
+    And DB_SSLMODE is "maybe"
+    When the settings are read
+    Then DB_SSLMODE is ignored and validation succeeds
+
+  Scenario Outline: Connection string built from variables
+    Given DB_HOST "<host>", DB_PORT "<port>", DB_USER "app", DB_NAME "cms", DB_SSLMODE "<sslmode>"
+    When the PostgreSQL DSN is built
+    Then the DSN targets "<host>:<expectedPort>" and database "cms"
+    And it sets sslmode "<expectedSslmode>"
+    And it sets the session time zone to UTC
+    And a password containing spaces, quotes, "@" or "/" is escaped so that parsing the DSN returns it unchanged
+
+    Examples:
+      | host     | port | expectedPort | sslmode     | expectedSslmode |
+      | db.local |      | 5432         |             | disable         |
+      | db.local | 5433 | 5433         | require     | require         |
+      | pg       | 5432 | 5432         | verify-full | verify-full     |
+
+  Scenario: Invalid SSL mode is rejected
+    Given DB_DRIVER is "postgres" and DB_SSLMODE is "maybe"
+    When the settings are read
+    Then startup fails naming DB_SSLMODE and the accepted values
+
+  Scenario Outline: Fail fast when the server cannot be used
+    Given DB_DRIVER is "postgres" and "<fault>"
+    When the server starts
+    Then startup stops with "Unable to open the database"
+    And the message names the host and port
+    And the message does not contain the DB_PASSWORD value
+
+    Examples:
+      | fault                                             |
+      | nothing listens on DB_PORT                        |
+      | the password is wrong                             |
+      | the database does not exist                       |
+      | the server requires TLS and DB_SSLMODE is disable |
+
+  Scenario: Data directory with PostgreSQL
+    Given DB_DRIVER is "postgres" and DATA_DIR is "/data"
+    Then update state, staging and backups live in "/data"
+    And DB_FILE is ignored
+
+  Scenario: Connection pool
+    Given DB_MAX_OPEN_CONNS 4, DB_MAX_IDLE_CONNS 2 and DB_CONN_MAX_LIFETIME_SECONDS 60
+    When the PostgreSQL connection is opened
+    Then the pool limits are 4 open, 2 idle and 60 seconds
+
+  Scenario: Migration on PostgreSQL
+    Given an empty PostgreSQL database
+    When database.Migrate runs
+    Then the tables articles, images, users, invites, api_keys and purge_settings exist in schema "public"
+    And the unique indexes on users and api_keys exist
+    And the first user lacking a role becomes "owner" and the others "admin"
+    And running database.Migrate a second time changes nothing
+
+  Scenario: Existing drivers are untouched by the PostgreSQL addition
+    Given a SQLite file holding rows, and a MySQL database holding rows
+    When database.Migrate runs on each
+    Then the schema and every row are unchanged on both
+
+  Scenario Outline: Repository behaviour is the same on every driver
+    Given the "<driver>" driver
+    Then the repository contract "<case>" holds
+
+    Examples:
+      | driver   | case                                                                  |
+      | postgres | create user and read it back with its id and timestamps               |
+      | postgres | username "Bob" and "bob" are distinct users                           |
+      | postgres | email "A@x.io" and "a@x.io" follow the same rule as on sqlite         |
+      | postgres | duplicate email returns an error and stores nothing                   |
+      | postgres | the failed duplicate insert leaves the connection usable              |
+      | postgres | unknown id returns domain ErrUserNotFound                             |
+      | postgres | accept invite twice: the second returns ErrInviteNotFound             |
+      | postgres | accept invite with a taken username leaves the invite unaccepted      |
+      | postgres | renew invite with unchanged values still succeeds                     |
+      | postgres | duplicate image hashes are grouped and counted                        |
+      | postgres | media search treats % and _ literally                                 |
+      | postgres | media search is case-sensitive exactly as on sqlite                   |
+      | postgres | article body of 1 MB round-trips                                      |
+      | postgres | article title with emoji and accents round-trips                      |
+      | postgres | zero reset expiration round-trips as a zero time                      |
+      | postgres | stored times read back in UTC                                         |
+      | postgres | purge settings save, then SaveLastRun with identical values succeeds  |
+      | postgres | api key unique hashed_key, revoke and last_used                       |
+      | postgres | offline article reads as not found publicly, online article is listed |
+      | postgres | listing order and pagination match sqlite for the same data           |
+
+  Scenario Outline: Backup before an update
+    Given the "<driver>" driver with a populated database
+    When the pre-update backup runs
+    Then a file "<pattern>" exists in DATA_DIR/backups
+    And only the 3 newest backups are kept
+    And a failure returns an error, so the update download fails instead of claiming a backup
+
+    Examples:
+      | driver   | pattern             |
+      | sqlite   | renewcms-<time>.db  |
+      | mysql    | renewcms-<time>.sql |
+      | postgres | renewcms-<time>.sql |
+
+  Scenario: PostgreSQL backup content
+    Given a PostgreSQL database with 2 users and 1 article
+    When the pre-update backup runs
+    Then the dump contains the schema, indexes and the rows of every table
+    And it does not contain the DB_PASSWORD value
+    And replaying it into an empty database restores the same rows
+    And sequences are reset so the next insert gets an unused id
+
+  Scenario: Secrets are never exposed
+    Given DB_DRIVER is "postgres"
+    Then no log line, error message or file in the repository contains the DB_PASSWORD value
+
+  Scenario: Static builds
+    Then the module builds with CGO_ENABLED=0 for the 6 task release targets

features/postgres_database_driver.qa.md

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+# QA: PostgreSQL database driver
+
+Backend only. Go tests in test/, black-box, no live server by default.
+
+Decisions: DB_DRIVER=postgres (alias postgresql), gorm.io/driver/postgres (pgx, pure Go), shared DB_* vars plus DB_SSLMODE, pure-Go logical dump backup, `task test:postgres` against postgres:16 and postgres:17, SQLite or MySQL to PostgreSQL migration is a documented manual export/import only.
+
+## Automated, no server (task test)
+1. Registry: contains sqlite, mysql and postgres. Alias "postgresql" resolves to postgres. "oracle" returns `unsupported database driver "oracle"`.
+2. Env validation: table-driven over Driver selection and Missing PostgreSQL variable. Invalid DB_SSLMODE or a non-numeric pool var returns an error naming the variable. DB_SSLMODE is ignored under sqlite and mysql. MySQL validation unchanged.
+3. DSN builder: table-driven over the DSN scenario. Parse the output with the pgx config parser and assert host, port, database, sslmode and the UTC time zone. Round-trip a password such as `s3cr3t/Value@42:x 'q'`. The form used in errors never contains the password.
+4. Settings.DataDir under postgres: DATA_DIR wins, DB_FILE ignored.
+5. Fail fast without a server: closed 127.0.0.1 port, 1s connect timeout. Error has the "Unable to open the database" prefix, mentions host and port, not the password.
+6. Pool settings via a stub opener or the real test below.
+7. Regression: the existing SQLite and MySQL tests pass unchanged. A pre-change SQLite fixture is unchanged after Migrate.
+8. Dump writer: reuse the existing formatter tests. Add PostgreSQL value formatting with a fake row source: bool as true/false, bytea hex escapes, timestamptz in UTC, NULL, identifier and string quoting.
+9. Migrate dialect handling: no MySQL table options are applied under postgres (tableOptionsFor).
+
+## Automated, real server (task test:postgres)
+Setup: the task runs `docker run` for postgres:16 then postgres:17, waits with pg_isready, exports RENEWCMS_TEST_POSTGRES_DSN, runs `go test -tags nofrontend ./test/... -run Postgres -count=1`, then removes the container. Tests t.Skip when the variable is unset. Repository contract tests are parameterised over sqlite, mysql and postgres with a fresh database each.
+10. Migrate on an empty database: tables and indexes via information_schema and pg_indexes, role backfill, idempotent second run.
+11. User create/read, case-sensitive username and email, duplicate email, ErrUserNotFound. After the unique violation the next query on the same pool succeeds.
+12. Invite accept twice, accept with a taken username (invite stays unaccepted), renew with unchanged values.
+13. Image duplicates grouping and counts (GROUP BY strictness), search with % and _ and its case rule, filename backfill listing.
+14. Article body 1 MB, unicode title, title lookup, online filter, listing order and pagination parity with sqlite.
+15. API key unique hashed_key, revoke, last_used.
+16. Zero-time round trip, UTC times.
+17. Purge settings upsert.
+18. Backup on a populated database: .sql file, 3-file retention, replay into a second empty database gives identical rows, no password in the file, next insert after replay gets a fresh id.
+19. Wrong password, missing database and TLS-required-but-disabled fail with the "Unable to open the database" prefix and no password.
+
+## Build and lint
+20. `task lint:go` and `task test` pass. `task test:postgres` passes on 16 and 17 (record both; NOT RUN if Docker is unavailable).
+21. `CGO_ENABLED=0 go build -tags nofrontend ./...` passes. Cross-compile the 6 `task release` targets.
+22. `task mutate` impact: none (useCases only).
+23. No comment lines in the added Go files.
+24. Layering: `go list -deps` on useCases and domain shows no pgx or gorm. Only api/dependecyInjection.go builds the postgres config.
+
+## Manual (needs Compose and real SMTP)
+25. docker-compose.postgres.yml: renewcms plus a postgres service with a named volume and a pg_isready healthcheck, depends_on service_healthy, DB_DRIVER=postgres, DB_HOST=postgres, DATA_DIR=/data. `docker compose up`: /healthz 200, register, log in, create an article, restart the stack, data persists.
+26. Stop the postgres container and start renewcms: clear error, no password in the logs.
+27. In the Docker image (uid 10001), trigger the backup path and confirm the .sql file lands under /data/backups.
+28. Docs: .env.example, docker.env.example, docs/configuration.md, docs/docker.md, docs/deployment.md, docs/development.md and the docs/architecture.md "Storage and database seams" section list DB_DRIVER=postgres, DB_SSLMODE and the manual migration note. DB_SSLMODE goes into cmd/server/main.go envDefaults.
+29. SQLite default end to end with no new vars set behaves as before.