feat(history): 消息搜索/编辑/删除 + 会话置顶(D2/D3/D5)

- history/message_ops.go(新): Search(会话内, q/after互斥, LIKE参数化+%/_转义+大小写不敏感, 严格限定会话doc) / UpdateMessage(返回更新后Message) / DeleteMessage / messageByID / escapeLike
- history/session_pin.go(新): SetPinned; 迁移0009 chat_sessions加pinned INTEGER DEFAULT 0; store.go SessionMeta.Pinned + createSessionsTable加列
- session_preview.go: 查询加s.pinned + ORDER BY pinned DESC,(type=main) DESC,created_at ASC
- gateway history_write.go(新,保持history.go≤500): handlePatchSession(pinned+title) / handlePatchMessage / handleDeleteMessage; server.go加PATCH/DELETE /api/v1/messages/{id} + /sessions/{id}置顶
- history.go: handleListMessages读q分流Search; 契约PATCH title/置顶
- D2会话内搜索(不做跨会话,隔离会话不外泄红线); D3不做重发端点(客户端编辑后再发); D5用pinned bool
- 测试(message_ops/history_messages/migrate_pinned), build/vet/test绿+3平台交叉编译; Docs/api-client v0.30
- 未做: 编辑/删除WS实时广播(message_edited/deleted), 下批

internal/runtime/history/message_ops.go

@@ -0,0 +1,113 @@
+package history
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// This file owns the single-message operations behind the Android collaboration batch
+// ③a (D2 search, D3 edit/delete). Both are strictly session-scoped or id-scoped: a
+// message is only ever reached through the session it belongs to (Search) or its own
+// opaque id (UpdateMessage/DeleteMessage), so an isolated group/stranger session can
+// never surface in another session's results (project red line).
+
+// Search returns up to limit messages for sessionID whose content contains query,
+// newest first. The match is a case-insensitive ASCII LIKE (SQLite's default for
+// LIKE) with the query's %/_/\ escaped so they match literally; before is the same
+// millisecond cursor as List (strictly older than before) and limit is clamped to
+// [1, maxPageLimit]. rowid breaks created_at ties so same-millisecond messages keep a
+// stable order. An empty query returns an empty (non-nil) slice — the caller uses
+// List for plain paging instead. Search never crosses the session boundary.
+func (s *Store) Search(ctx context.Context, sessionID, query string, before int64, limit int) ([]Message, error) {
+	limit = clampLimit(limit)
+	if query == "" {
+		return make([]Message, 0), nil
+	}
+	sqlText := `SELECT id, session_id, role, content, mode, mood, image, thinking, platform, device_id, sender_name, adapter_id, created_at
+		FROM chat_messages WHERE session_id = ? AND content LIKE ? ESCAPE '\'`
+	args := []any{sessionID, "%" + escapeLike(query) + "%"}
+	if before > 0 {
+		sqlText += ` AND created_at < ?`
+		args = append(args, before)
+	}
+	sqlText += ` ORDER BY created_at DESC, rowid DESC LIMIT ?`
+	args = append(args, limit)
+
+	rows, err := s.db.QueryContext(ctx, sqlText, args...)
+	if err != nil {
+		return nil, fmt.Errorf("history: search %s: %w", sessionID, err)
+	}
+	defer func() { _ = rows.Close() }()
+
+	msgs := make([]Message, 0)
+	for rows.Next() {
+		m, err := scanMessage(rows)
+		if err != nil {
+			return nil, fmt.Errorf("history: scan search %s: %w", sessionID, err)
+		}
+		msgs = append(msgs, m)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("history: iterate search %s: %w", sessionID, err)
+	}
+	return msgs, nil
+}
+
+// UpdateMessage replaces the content of the message with id and returns the updated
+// message (like AppendFull, so the caller can return/broadcast it without a second
+// read). Only content changes; role, platform, timestamps and the rest stay as stored.
+// An unknown id returns ErrMessageNotFound.
+func (s *Store) UpdateMessage(ctx context.Context, id, content string) (Message, error) {
+	res, err := s.db.ExecContext(ctx, `UPDATE chat_messages SET content = ? WHERE id = ?`, content, id)
+	if err != nil {
+		return Message{}, fmt.Errorf("history: update message %s: %w", id, err)
+	}
+	n, err := res.RowsAffected()
+	if err != nil {
+		return Message{}, fmt.Errorf("history: update message %s rows: %w", id, err)
+	}
+	if n == 0 {
+		return Message{}, fmt.Errorf("history: update message %s: %w", id, ErrMessageNotFound)
+	}
+	return s.messageByID(ctx, id)
+}
+
+// DeleteMessage removes a single message. An unknown id returns ErrMessageNotFound.
+func (s *Store) DeleteMessage(ctx context.Context, id string) error {
+	res, err := s.db.ExecContext(ctx, `DELETE FROM chat_messages WHERE id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("history: delete message %s: %w", id, err)
+	}
+	n, err := res.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("history: delete message %s rows: %w", id, err)
+	}
+	if n == 0 {
+		return fmt.Errorf("history: delete message %s: %w", id, ErrMessageNotFound)
+	}
+	return nil
+}
+
+// messageByID reads one message by id, returning ErrMessageNotFound when the row is
+// absent.
+func (s *Store) messageByID(ctx context.Context, id string) (Message, error) {
+	row := s.db.QueryRowContext(ctx, `SELECT id, session_id, role, content, mode, mood, image, thinking, platform, device_id, sender_name, adapter_id, created_at
+		FROM chat_messages WHERE id = ?`, id)
+	m, err := scanMessage(row)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return Message{}, fmt.Errorf("history: read message %s: %w", id, ErrMessageNotFound)
+		}
+		return Message{}, fmt.Errorf("history: read message %s: %w", id, err)
+	}
+	return m, nil
+}
+
+// escapeLike escapes the LIKE wildcards in a user query so %, _ and \ match literally
+// (the caller pairs it with ESCAPE '\'). It is applied before the %...% wrapping.
+func escapeLike(query string) string {
+	return strings.NewReplacer(`\`, `\\`, `%`, `\%`, `_`, `\_`).Replace(query)
+}