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/psql.go

@@ -0,0 +1,137 @@
+package psql
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+	"time"
+
+	"git.t-juice.club/torjus/oubliette/internal/shell"
+)
+
+const sessionTimeout = 5 * time.Minute
+
+// PsqlShell emulates a PostgreSQL psql interactive terminal.
+type PsqlShell struct{}
+
+// NewPsqlShell returns a new PsqlShell instance.
+func NewPsqlShell() *PsqlShell {
+	return &PsqlShell{}
+}
+
+func (p *PsqlShell) Name() string        { return "psql" }
+func (p *PsqlShell) Description() string { return "PostgreSQL psql interactive terminal" }
+
+func (p *PsqlShell) Handle(ctx context.Context, sess *shell.SessionContext, rw io.ReadWriteCloser) error {
+	ctx, cancel := context.WithTimeout(ctx, sessionTimeout)
+	defer cancel()
+
+	dbName := configString(sess.ShellConfig, "db_name", "postgres")
+	pgVersion := configString(sess.ShellConfig, "pg_version", "15.4")
+
+	// Print startup banner.
+	fmt.Fprint(rw, startupBanner(pgVersion))
+
+	var sqlBuf []string // accumulates multi-line SQL
+
+	for {
+		prompt := buildPrompt(dbName, len(sqlBuf) > 0)
+		if _, err := fmt.Fprint(rw, prompt); err != nil {
+			return nil
+		}
+
+		line, err := shell.ReadLine(ctx, rw)
+		if errors.Is(err, io.EOF) {
+			return nil
+		}
+		if err != nil {
+			return nil
+		}
+
+		trimmed := strings.TrimSpace(line)
+
+		// Empty line in non-buffering state: just re-prompt.
+		if trimmed == "" && len(sqlBuf) == 0 {
+			continue
+		}
+
+		// Backslash commands dispatch immediately (even mid-buffer they cancel the buffer).
+		if strings.HasPrefix(trimmed, `\`) {
+			sqlBuf = nil // discard any partial SQL
+
+			result := dispatchBackslash(trimmed, dbName)
+			if result.output != "" {
+				output := strings.ReplaceAll(result.output, "\n", "\r\n")
+				fmt.Fprintf(rw, "%s\r\n", output)
+			}
+
+			if sess.Store != nil {
+				if err := sess.Store.AppendSessionLog(ctx, sess.SessionID, trimmed, result.output); err != nil {
+					return fmt.Errorf("append session log: %w", err)
+				}
+			}
+			if sess.OnCommand != nil {
+				sess.OnCommand("psql")
+			}
+
+			if result.exit {
+				return nil
+			}
+			continue
+		}
+
+		// Accumulate SQL lines.
+		sqlBuf = append(sqlBuf, line)
+
+		// Check if the statement is terminated by a semicolon.
+		if !strings.HasSuffix(strings.TrimSpace(line), ";") {
+			continue
+		}
+
+		// Full statement ready — join and dispatch.
+		fullSQL := strings.Join(sqlBuf, " ")
+		sqlBuf = nil
+
+		result := dispatchSQL(fullSQL, dbName, pgVersion)
+		if result.output != "" {
+			output := strings.ReplaceAll(result.output, "\n", "\r\n")
+			fmt.Fprintf(rw, "%s\r\n", output)
+		}
+
+		if sess.Store != nil {
+			if err := sess.Store.AppendSessionLog(ctx, sess.SessionID, fullSQL, result.output); err != nil {
+				return fmt.Errorf("append session log: %w", err)
+			}
+		}
+		if sess.OnCommand != nil {
+			sess.OnCommand("psql")
+		}
+
+		if result.exit {
+			return nil
+		}
+	}
+}
+
+// buildPrompt returns the psql prompt. continuation is true when buffering multi-line SQL.
+func buildPrompt(dbName string, continuation bool) string {
+	if continuation {
+		return dbName + "-# "
+	}
+	return dbName + "=# "
+}
+
+// configString reads a string from the shell config map with a default.
+func configString(cfg map[string]any, key, defaultVal string) string {
+	if cfg == nil {
+		return defaultVal
+	}
+	if v, ok := cfg[key]; ok {
+		if s, ok := v.(string); ok && s != "" {
+			return s
+		}
+	}
+	return defaultVal
+}