feat: nest join ON conditions as Query objects

[abnegate]

Summary

• Adds Query::on($left, $right, $op = '=') for column-to-column join ON conditions.
• Overloads join / leftJoin / rightJoin / fullOuterJoin so the second or third argument can be an array of ON queries:
  • simple (unchanged): leftJoin('orders', '$id', 'customerId', '=', 'ord')
  • nested, no alias: leftJoin('orders', [Query::on('$id', 'customerId'), Query::equal('ord.status', ['paid'])])
  • nested, with alias: leftJoin('orders', 'ord', [Query::on('$id', 'customerId'), Query::equal('ord.status', ['paid'])])
• Nested ON conditions compile onto the JOIN (not WHERE), so LEFT JOIN semantics stay correct.
• Parse/toArray round-trip nested join values; AST path ANDs ON expressions.

Wire format

{
  "method": "leftJoin",
  "attribute": "orders",
  "values": [
    "ord",
    {"method": "on", "values": ["$id", "=", "customerId"]},
    {"method": "equal", "attribute": "ord.status", "values": ["paid"]}
  ]
}

Simple triples are unchanged.

Test plan

• Unit tests for factories, parse round-trip, compile, AST
• composer test (one unrelated xdebug nesting flake in ParserTest)
• composer lint / composer check

[github-actions]

📊 Coverage

Metric	Covered	Ratio
Lines	91.88%	7559 / 8227
Methods	83.89%	1114 / 1328
Classes	65.45%	144 / 220

Full per-file breakdown in the job summary.

[greptile-apps]

Greptile Summary

The PR adds Query-based nested JOIN conditions with serialization, SQL compilation, AST conversion, predicate validation, and alias qualification.

• Introduces Query::on() and overloaded JOIN factories for arrays of ON predicates
• Preserves nested JOIN queries through parsing and serialization
• Compiles supported predicates directly into JOIN ON clauses
• Adds corresponding API, SQL, parsing, and AST coverage

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/Query/Builder.php	Adds nested JOIN SQL/AST compilation, shared predicate validation, and AST alias qualification.
src/Query/Query.php	Adds nested JOIN factories, alias and predicate accessors, parsing support, and recursive serialization.
src/Query/Method.php	Adds the On query method used for column-to-column JOIN conditions.
tests/Query/API/JoinTest.php	Covers nested JOIN construction, validation, compilation, aliases, and shape generation.
tests/Query/AST/BuilderAstTest.php	Covers nested JOIN AST conditions, supported predicates, and alias qualification.

_{Reviews (3): Last reviewed commit: "fix: qualify nested join ON columns in A..." | Re-trigger Greptile}

[abnegate]

@greptileai review

[abnegate]

@greptileai review