feat: narrow toBeInstanceOf() subjects across ->and() chains

[maks-oleksyuk]

Problem

expect($x)->toBeInstanceOf(Y::class) only narrows PHPStan's known type for $x when that's the entire statement, on its own. Two related, common patterns weren't covered:

1. Within a chain: expect($items[0])->toBeInstanceOf(Post::class)->and($items[0]->title)->toBe('hello'); — $items[0]->title needs $items[0] narrowed, but that read happens before the statement finishes, and PHPStan's native statement-level narrowing only ever applies to code after a condition/statement — it can't reach into an earlier part of the same expression.
2. Past a chained statement: expect($response)->toBeInstanceOf(JsonResponse::class)->and($response->getStatusCode())->toBe(200); followed on the next line by decodeJsonBody($response); — narrowing didn't survive, because toBeInstanceOf() wasn't the chain's outermost call.

Both are extremely common Pest idioms (asserting a value's type, then immediately reading properties/methods off it, often chained with other assertions via ->and()), and without this, every real-world use forces either splitting the assertion into an awkward standalone statement or falling back to a manual assert($x instanceof Y);.

Fix

Two complementary extensions, because they hook into genuinely different PHPStan mechanisms:

• ExpectationChainSubjectNarrowingExtension (ExpressionTypeResolverExtension) — narrows a subject reused later in the same chain. Re-parses the file (via the existing PestFileDiscoverer), walks each statement's own ->var chain spine (never descending into closures — that would leak a fact from one it() block into a sibling one), and matches subjects structurally against earlier toBeInstanceOf() steps in the same statement, by source position.
• ExpectationInstanceTypeSpecifyingExtension (MethodTypeSpecifyingExtension) — walks the entire chain via ->var to collect every toBeInstanceOf() step, not just the outermost call, so narrowing correctly survives for code after the whole statement — using PHPStan's native scope-tracking, which already handles reassignment, branches, and loops correctly, unlike the position-based approach above.

These can't be merged into one extension: the "within-chain" one is a text/position-based workaround with no notion of control flow (deliberately scoped to within one statement, where that's safe), while the "past-statement" one needs PHPStan's real scope machinery, which PHPStan only ever invokes for a statement's outermost expression — it structurally cannot see into a sub-expression mid-statement.

Shared and()/expect() subject-resolution logic lives in one ExpectationChainSubjectResolver service both extensions inject, rather than being duplicated.

Testing

• New assertType coverage: expectation-chain-subject-narrowing.php (8 cases — array/plain-variable subjects, multiple distinct subjects narrowed in one chain, position-ordering guards, no leaking into an unrelated it() block) and expectation-instance-narrowing.php (+3 cases — chained toBeInstanceOf() narrowing past the statement, multiple follow-up steps, and()-introduced subject narrowing past the statement).
• pest --parallel: 482 passed. phpstan analyse: no errors. pint / rector --dry-run: clean.
• Verified against real-world usage in a consuming app: expect($x)->toBeInstanceOf(Y)->and(...)->and(...); chains that previously required assert() workarounds or splitting across statements now type-check cleanly as a single chain, both mid-chain and for code after.