feat: add psql shell and username-to-shell routing

Add a PostgreSQL psql interactive terminal shell with backslash
meta-commands, SQL statement handling with multi-line buffering, and
canned responses for common queries. Add username-based shell routing
via [shell.username_routes] config (second priority after credential-
specific shell, before random selection). Bump version to 0.13.0.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/shell/psql/commands.go

@@ -0,0 +1,123 @@
+package psql
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+// commandResult holds the output of a command and whether the session should end.
+type commandResult struct {
+	output string
+	exit   bool
+}
+
+// dispatchBackslash handles psql backslash meta-commands.
+func dispatchBackslash(cmd, dbName string) commandResult {
+	// Normalize: trim spaces after the backslash command word.
+	parts := strings.Fields(cmd)
+	if len(parts) == 0 {
+		return commandResult{output: "Invalid command \\. Try \\? for help."}
+	}
+
+	verb := parts[0] // e.g. `\q`, `\dt`, `\d`
+	args := parts[1:]
+
+	switch verb {
+	case `\q`:
+		return commandResult{exit: true}
+	case `\dt`:
+		return commandResult{output: listTables()}
+	case `\d`:
+		if len(args) == 0 {
+			return commandResult{output: listTables()}
+		}
+		return commandResult{output: describeTable(args[0])}
+	case `\l`:
+		return commandResult{output: listDatabases()}
+	case `\du`:
+		return commandResult{output: listRoles()}
+	case `\conninfo`:
+		return commandResult{output: connInfo(dbName)}
+	case `\?`:
+		return commandResult{output: backslashHelp()}
+	case `\h`:
+		return commandResult{output: sqlHelp()}
+	default:
+		return commandResult{output: fmt.Sprintf("Invalid command %s. Try \\? for help.", verb)}
+	}
+}
+
+// dispatchSQL handles SQL statements (already accumulated and semicolon-terminated).
+func dispatchSQL(sql, dbName, pgVersion string) commandResult {
+	// Strip trailing semicolon and whitespace for matching.
+	trimmed := strings.TrimRight(sql, "; \t")
+	trimmed = strings.TrimSpace(trimmed)
+	upper := strings.ToUpper(trimmed)
+
+	switch {
+	case upper == "SELECT VERSION()":
+		ver := fmt.Sprintf("PostgreSQL %s on x86_64-pc-linux-gnu, compiled by gcc (GCC) 13.2.0, 64-bit", pgVersion)
+		return commandResult{output: formatSingleValue("version", ver)}
+	case upper == "SELECT CURRENT_DATABASE()":
+		return commandResult{output: formatSingleValue("current_database", dbName)}
+	case upper == "SELECT CURRENT_USER":
+		return commandResult{output: formatSingleValue("current_user", "postgres")}
+	case upper == "SELECT NOW()":
+		now := time.Now().UTC().Format("2006-01-02 15:04:05.000000+00")
+		return commandResult{output: formatSingleValue("now", now)}
+	case upper == "SELECT 1":
+		return commandResult{output: formatSingleValue("?column?", "1")}
+	case strings.HasPrefix(upper, "INSERT"):
+		return commandResult{output: "INSERT 0 1"}
+	case strings.HasPrefix(upper, "UPDATE"):
+		return commandResult{output: "UPDATE 1"}
+	case strings.HasPrefix(upper, "DELETE"):
+		return commandResult{output: "DELETE 1"}
+	case strings.HasPrefix(upper, "CREATE TABLE"):
+		return commandResult{output: "CREATE TABLE"}
+	case strings.HasPrefix(upper, "CREATE DATABASE"):
+		return commandResult{output: "CREATE DATABASE"}
+	case strings.HasPrefix(upper, "DROP TABLE"):
+		return commandResult{output: "DROP TABLE"}
+	case strings.HasPrefix(upper, "ALTER TABLE"):
+		return commandResult{output: "ALTER TABLE"}
+	case upper == "BEGIN":
+		return commandResult{output: "BEGIN"}
+	case upper == "COMMIT":
+		return commandResult{output: "COMMIT"}
+	case upper == "ROLLBACK":
+		return commandResult{output: "ROLLBACK"}
+	case upper == "SHOW SERVER_VERSION":
+		return commandResult{output: formatSingleValue("server_version", pgVersion)}
+	case upper == "SHOW SEARCH_PATH":
+		return commandResult{output: formatSingleValue("search_path", "\"$user\", public")}
+	case strings.HasPrefix(upper, "SET "):
+		return commandResult{output: "SET"}
+	default:
+		// Extract the first token for the error message.
+		firstToken := strings.Fields(trimmed)
+		token := trimmed
+		if len(firstToken) > 0 {
+			token = firstToken[0]
+		}
+		return commandResult{output: fmt.Sprintf("ERROR:  syntax error at or near \"%s\"\nLINE 1: %s\n        ^", token, trimmed)}
+	}
+}
+
+// formatSingleValue formats a single-row, single-column psql result.
+func formatSingleValue(colName, value string) string {
+	width := max(len(colName), len(value))
+
+	var b strings.Builder
+	// Header
+	fmt.Fprintf(&b, " %-*s \n", width, colName)
+	// Separator
+	b.WriteString(strings.Repeat("-", width+2))
+	b.WriteString("\n")
+	// Value
+	fmt.Fprintf(&b, " %-*s\n", width, value)
+	// Row count
+	b.WriteString("(1 row)")
+	return b.String()
+}