tests: running run-tests.php deletes legacy tracked .php test files that share a basename with .phpt

[s2x]

Problem

Running the test suite (php run-tests.php -n tests/) silently deletes tracked legacy test files tests/<name>.php whenever a tests/<name>.phpt with the same basename exists.

Observed during the #177 session: a full suite run deleted 49–50 legacy files from the working tree (restored manually with git checkout -- tests/).

Root cause

run-tests.php (bundled from php-src) derives the executable path from the .phpt basename in the same directory and unlinks it unconditionally — with no guard against deleting pre-existing/git-tracked files:

// run-tests.php:1942 / 1952
$main_file_name = basename($file, 'phpt');
$test_file = $test_dir . DIRECTORY_SEPARATOR . $main_file_name . 'php';

// run-tests.php:1982–1991 — runs before every test, no existence check
// unlink old test results
@unlink($test_file);   // ← deletes a pre-existing tracked file too

The file is then overwritten with generated test code (save_text($test_file, ...), line 2276) and unlinked again after the run (line 2618) unless --keep-php is used. --keep-php does not prevent the pre-test unlink at line 1991.

Impact

• git status shows dozens of unexpected deletions after any suite run
• Risk of accidentally committing mass deletions
• 50 tracked .php files in tests/ currently share a basename with a .phpt (legacy migrated tests awaiting removal per migration task chore: cleanup php/ directory — move examples, remove embeddings.php #24)

Reproduction (empirical, verified)

ls tests/bug_0002.php          # exists (tracked in git)
php -n run-tests.php --no-progress tests/bug_0002.phpt >/dev/null 2>&1
ls tests/bug_0002.php          # No such file or directory
git checkout -- tests/bug_0002.php

Suggested fixes

1. Recommended: delete the 50 legacy .php files from git in a dedicated migration PR (they are fully superseded by .phpt; task chore: cleanup php/ directory — move examples, remove embeddings.php #24) — removes the root hazard
2. Add a sanity guard (script or CI pre-check) that refuses to run the suite while tracked .php files overlap with .phpt basenames
3. Document in AGENTS.md that suite runs mutate tests/ until the migration lands