feat: terminal CLI with interactive SQL shell

[debba]

Summary

Tabularis now works from the terminal. The binary gains a set of clap subcommands that reuse the same connection resolution as the MCP server (keychain passwords, SSH/K8s tunnels, plugin drivers), so every saved connection is reachable from a script or a shell session, addressed by connection id or name. No Tauri runtime is started in this mode.

Command map

Command	Description
tabularis connections (ls)	List saved connections (table or --json)
tabularis databases <conn>	List databases on the server
tabularis schemas <conn>	List schemas
tabularis tables <conn>	List tables (-d, --schema, --json)
tabularis describe <conn> <table>	Columns, indexes, foreign keys
tabularis query <conn> [SQL] (q)	One-shot query, stdin pipe, or interactive shell
tabularis install-cli	Symlink the binary into a PATH directory

query picks its mode from the invocation: SQL argument → one-shot; piped stdin → executes the piped statement; interactive TTY with no SQL → opens the shell.

Output formats: aligned ASCII table (default), --format json (array of row objects), --format csv. Result data goes to stdout and logs to stderr, so piping stays clean. Non-zero exit code on failure.

$ tabularis query tabularis-demo-mysql "select id, name from customers" --format csv > customers.csv
$ echo "select count(*) from orders" | tabularis q tabularis-demo-mysql

Interactive shell

tabularis query <conn> opens a REPL backed by rustyline: line editing, persistent history (cli_history.txt in the app config dir), multi-line statements executed on a terminating ;, Ctrl-C drops the current buffer, Ctrl-D exits. Meta commands:

\l    list databases        \f table|json|csv   output format
\dn   list schemas          \limit N            row limit (0 = unlimited)
\dt   list tables           \schema NAME        set schema
\d T  describe table        \use DB             switch database
\q    quit                  \?                  help

Multi-database connections

Multi-db connections resolve to their first database, which made the remaining ones unreachable outside the GUI. All db-scoped commands now accept -d/--database, and the shell adds \use <db>: the switch is validated with a connection test before being applied, and the prompt shows the active database (Demo · MySQL:blog_demo>). This reuses the GUI's per-call database override semantics (DatabaseSelection::Single).

Internals

• The connection-resolution helpers that lived in mcp/mod.rs (keychain lookup, SSH/K8s expansion, driver registration) moved to a shared headless.rs; the MCP server now wraps them with its JSON-RPC error type. No behavior change on the MCP side.
• keychain_utils logged via println!, which polluted stdout (a problem once stdout carries parseable CSV/JSON) and bypassed the in-app log buffer. It now goes through the log crate.
• Headless processes never called sqlx::any::install_default_drivers(), so the default test_connection path panicked. It is now installed in headless::register_drivers(), which also covers --mcp.
• CLI argument parsing keeps the GUI-launch fallback: unknown arguments (macOS -psn_*) still boot the GUI, while misspelled subcommands and bad flag values surface clap's error instead of silently opening a window.

Tests

37 new unit tests: clap parsing (GUI fallback error kinds, value enums, aliases), table/CSV/JSON rendering (alignment, control-character escaping, quoting), limit and database-override semantics, and the install-cli symlink logic (idempotency, refusal to clobber foreign files, --force). Full suite: 692 passing.

Manually exercised against the demo MySQL connection: one-shot queries, stdin pipes, the shell with \use across the three demo databases, and install-cli into a scratch directory.

Known limitations

• On Windows release builds the binary has no attached console (windows_subsystem = "windows"), so CLI output is invisible there. Same constraint as the existing --mcp mode.
• Each shell statement runs on its own pooled connection: session state (SET, transactions, temp tables) does not persist between statements. Stated in \?.

Notes

This PR doubled as an experiment in agent-driven development: implementation, tests, and this description were produced end to end with Fable 5 (Anthropic), with human direction and review throughout.