[PHP] Resume file-backed db-pull from flushed cursor boundaries

[adamziel]

A new db-pull process now continues file output from the last flushed byte and source cursor boundary instead of silently starting the lifecycle over.

Background

Exit code 2 leaves completion_state=partial. Direct db-pull previously recognized only in_progress, so a later process replaced the partial lifecycle. A hard stop could also leave db.sql ahead of or behind the saved source cursor without a reliable way to classify those bytes.

This change

File pulls write database-dump.intent before starting and save the source cursor only after the matching db.sql bytes have been flushed. Resume truncates an unconfirmed tail, rejects a missing or shorter file, and refuses an output-mode change. Every file request asks for replacement-table SQL. A completed SHA-256 record confirms the resulting dump only after the source reports completion.

db-apply refuses an intent-marked prefix; safe replay of a completed replacement dump is added by #595.

This is PR 2 of 5 in the database restart stack: #590 → #591 → #595 → #582 → #607.

Testing

Focused tests cover exit-code-2 continuation through the database-index stage, two process deaths around the first SQL checkpoint, missing and shortened local artifacts, output-mode drift, and rejection of an unfinished dump by db-apply.

• DatabaseCommandRestartTest
• import-54-db-pull-index-interruption
• import-59

[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	9.36 s	9.56 s	⚪ -199 ms (-2.1%)	✓	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	3.63 s	3.57 s	⚪ +56 ms (+1.6%)	✓	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	12.98 s	13.13 s	⚪ -143 ms (-1.1%)

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

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