[PHP] Stop pull-db cleanly during database apply

[adamziel]

pull-db now handles SIGINT and SIGTERM while it is applying the database, exits with code 2, and leaves the database-apply stage unfinished for the next process.

Background

The wrapper kept its normal signal handler while db-apply was running. A signal could therefore kill the process during an active PDO query. If db-apply returned partial, the wrapper also called it again immediately in the same process.

This change

The wrapper uses the database-apply signal policy only for that stage and restores its normal policy afterward. Pending signals are handled between SQL chunks, not during a target query.

db-apply runs once per wrapper process. A partial result sets exit code 2 and returns without marking the stage or the whole pull complete. The next process uses #595 to start db.sql again from the beginning.

This is PR 4 of 5: #590 → #591 → #595 → #582 → #607.

Testing

The focused PHP tests cover the partial result, next-process completion, restoration after an exception, and the actual PCNTL handlers and signal mask. The MySQL E2E blocks a target query, sends SIGTERM, checks exit code 2 and the unchanged stage, then completes the pull in a new process.

[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	9.91 s	9.70 s	⚪ +212 ms (+2.2%)	✓	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	3.77 s	3.75 s	⚪ +21 ms (+0.6%)	✓	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	13.69 s	13.46 s	⚪ +232 ms (+1.7%)

_{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.