[larspohlmann]

Closes #25

What & why

A method whose only touch of a parameter is handing it to a PHP built-in (trim, str_replace, parse_url, array_map, …) was scored as a pass-through hop, with the chain terminating external. But the value cannot travel any further inside user code once it enters a built-in — that method is the consumer. Counting it as a hop made every chain ending in a built-in one hop too long (see #25 for the measured impact).

The fix, in two layers:

• CallResolver returns a new InternalFunctionUse resolution when a function is absent from the index and PHP-internal (function_exists + ReflectionFunction::isInternal). A function that is absent but not internal (vendor code, an unseen user helper) still terminates as external, since the value may forward on there.
• ChainTraversal treats an InternalFunctionUse forward as a used terminal at the current method rather than a scored hop. An origin that only feeds its own parameter to a built-in is not tramp data and is dropped (no 0-hop findings).

Callback-taking built-ins (array_map, usort, call_user_func) are internal too, so the conservative "the argument is consumed" choice from #25 falls out for free.

Frozen-semantics flag: a forward into a PHP internal function is a use — one step stronger than the existing "external targets terminate" rule. Recorded by the internal-function-use fixture.

Real-world validation

On simple-feed-reader/backend (the codebase #25 measured), with its phptramp.dist.json (limit 4, warnLimit 3, minClasses 2):

	findings
before (develop)	26
after (this branch)	13

Same result as --exclude-terminal external (13) — but by shortening chains, not dropping them. Verified every remaining finding's origin exists in the baseline: zero new chains introduced; the fix only shortens or removes.

Checklist

• composer check is green (cs + stan + md + test)
• composer infection:diff is green (MSI 95%; the one escaped diff-scoped mutant is a verified equivalent mutant — removing the guard continue leaves output byte-identical, confirmed by running the full suite with the mutation applied)
• Semantic changes come with a fixture under tests/fixtures/ (internal-function-use)
• Title is a conventional commit with the issue number
• Targets develop (never main)