[maintainability] Driver configuration is an untyped raw array everywhere, with scattered ad-hoc casts

[corgab]

Summary

Driver configuration flows through the codebase as a bare array $config (the constructor-promoted protected readonly array $config in AbstractQuantumDriver), read at each use site with $this->config['key'] ?? default plus an inline, ad-hoc cast — confirmed 7 such reads across AbstractQuantumDriver and AwsBraketDriver: (int) ($this->config['entropy_qubits'] ?? 16), $this->config['max_qubits'] ?? null then later (int) $ceiling, ($this->config['synchronous_safe'] ?? true) === false, $this->config['pricing'] ?? [] (twice), $this->config['max_cost_per_run'] ?? null then later (float) $ceiling. There is no shape validation at construction time — a typo'd config key ('max_qubit' instead of 'max_qubits') fails silently by falling through to the ?? default branch, with no way to distinguish "intentionally unset" from "misspelled."

Where

• src/Drivers/AbstractQuantumDriver.php:119 (requiredConfig()/assertConfigured() — presence-only check, no type validation), 144-156 (assertWithinQubitCeiling()), 351 (generateEntropy())
• src/Drivers/AwsBraketDriver.php:36 (beforeExecution()), 76,121 (pricing), 113-140 (assertWithinCostCeiling())

This is the general/architectural counterpart of a concrete bug already filed separately: a non-numeric max_qubits/max_cost_per_run env value silently casts to 0 rather than failing clearly (see the linked issue on config/aether.php's uncast env() calls) — that bug is a direct symptom of config having no typed shape anywhere in the pipeline.

Refactor proposal

Introduce typed DriverConfig value object(s) — e.g. a base one for common keys (entropyQubits, maxQubits) and an AwsDriverConfig extension for region/bucket/deviceArn/pricing/maxCostPerRun — constructed once from the raw array (with is_numeric() validation raising InvalidDriverConfigException for a garbage value instead of silently casting), then passed to drivers instead of the raw array. Every $this->config['key'] ?? default + cast pair collapses to a single typed property/method access.

Severity: medium