[abkrim]

Resolves the ApplyDefaultInsteadOfNullCoalesceRector split from AID-531 — the opposite way from mechanical application: the two flagged sites are fixed by hand, and the rule stays armed as the gate's guard.

What the rule actually does (ticket premise corrected)

Not the classic ??→?: trap: it rewrites helper('key') ?? $default into helper('key', $default). That form still has a non-equivalent corner — a key present with explicit null returns $default under ??, but null under the parameter form.

What the review found at the two sites

Both read config('unblock.hq.ttl') ?? 7200. The corner is unreachable by construction: config/unblock.php defines the key as (int) env('HQ_WHITELIST_TTL', 14000) — always present, always int. Which exposed the real defect:

• the ?? 7200 was dead code, and
• a phantom default: the code (and its // Default 2 hours comment) claimed 7200 while the real default is 14000, owned by the config file.

Both fallbacks removed → the default has a single owner. Sanity-checked: config('unblock.hq.ttl') = 14000 (int).

The suite caught what reachability analysis alone could not

One test pinned the phantom fallback by fabricating the impossible state: config()->set('unblock.hq.ttl', null) at runtime, then asserting 7200. "Not configured" really means the env var is absent — in which case config resolves 14000 at load time; null never occurs. The test was the fallback's only consumer, and it consumed a state that cannot exist (the recorded lesson: a test that constructs the state directly is testing its own setup). It now pins the real contract: config-owned 14000 flowing through to the mailable, with an explicit expect(config(...))->toBe(14000) guard.

The rule stays enabled as a guard

• Zero-diff after the hand fix (refactor:dry exit 0, cleared cache)
• Proven to bite: a new config('x') ?? $default → rc=2 naming app/ProbeCoalesce.php
• Future config('x') ?? $d is always either dead or a duplicated default; if a genuinely present-but-null key ever appears, skip that call site — not the rule

Gates

composer check-full → exit 0, 1442 passed / 16 skipped (3585 assertions), coverage 89.8%.