[PHP] Download db.sql before applying MySQL database pulls

[adamziel]

db-pull --sql-output=mysql now downloads all of db.sql before it changes MySQL.

Background

The direct MySQL path executed SQL while it arrived. If that process stopped, the saved source position could not say whether MySQL committed, rolled back, or was still running a query.

This change

MySQL output now uses the database-only pull sequence: preflight, file-backed db-pull, then db-apply. The existing MySQL options become target options for db-apply, and the direct mysqli::multi_query() path is removed.

A stopped download continues from the last saved file size and source position. MySQL remains untouched until the download finishes. If applying the SQL stops, the next process opens a new connection and starts db.sql from the beginning. That runs the SQL mode, foreign-key, unique-check, and autocommit settings again.

Existing unfinished direct-MySQL work remains rejected instead of being guessed or converted.

This is PR 5 of 5: #590 → #591 → #595 → #582 → #607.

Testing

The focused E2E stops after a file position is saved, checks that MySQL is still untouched, runs the same command again, and compares the finished target with the source. Its tables also require the SQL mode and foreign-key settings from the dump header.

[github-actions]

Pull pipeline performance — large-directory

Site: large-directory · 2,000+ plus targeted file-transfer scenarios files · 10,000 posts · 25,000 postmeta · PHP 8.5.9

Stage	PR	trunk	Δ	Status	Details
playground-sqlite-db-pull	9.84 s	9.93 s	⚪ -95 ms (-1.0%)	✓	condition=db-pull in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=lexer native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=selected trunk: condition=db-pull in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=lexer native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=selected
playground-sqlite-db-apply	3.83 s	3.83 s	⚪ -3 ms (-0.1%)	✓	condition=db-apply to SQLite in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=parser native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=verified native_ast=WP_MySQL_Native_Parser_Node sqlite_driver_parser=verified trunk: condition=db-apply to SQLite in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=parser native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=verified native_ast=WP_MySQL_Native_Parser_Node sqlite_driver_parser=verified
Total	13.67 s	13.76 s	⚪ -99 ms (-0.7%)

_{Numbers carry runner noise; treat single-run deltas as directional, not authoritative.}

_{📈 Trunk performance history — commit-by-commit timeline.}

[adamziel]

Closing this draft. It is being replaced by a smaller target-database checkpoint stack.