tests: pre-installed zvec PHP extension (v0.4.10) shadows FFI classes — suite must run with -n

[s2x]

Problem

On machines where the legacy zvec PHP extension (v0.4.10, php-ext/) is installed via php.ini, require src/ZVec.php returns early and FFI-only classes never load — e.g. Class "ZVecIndexParams" not found in tests/test_index_params.phpt.

Root cause

src/ZVec.php:9 bails out before loading any PHP classes when the legacy extension is present:

if (extension_loaded('zvec')) return;

The installed extension (v0.4.10) defines only the older classes (ZVec, ZVecSchema, ZVecDoc, ZVecVectorQuery, …) but not the newer FFI-only helper classes — ZVecIndexParams, ZVecGroupByVectorQuery, ZVecCollectionStats, ZVecFieldSchema. Because of the early return, the class_alias block at the bottom of src/ZVec.php (lines 2428–2442) never runs.

Verification

php -m | grep zvec                          # zvec (v0.4.10)
php -n -r 'var_dump(extension_loaded("zvec"), extension_loaded("ffi"));'
# bool(false) bool(true)                    # -n fixes it
php -r 'require "src/ZVec.php"; var_dump(class_exists("ZVecIndexParams"));'
# bool(false)

Pre-existing: introduced in commit c2f0c7f (#25), independent of the v0.6.0 migration (#171–#177).

Workaround (current)

Run the suite with php run-tests.php -n tests/ (run-tests passes -n to child PHP processes — line 474), which disables the extension and loads the full FFI class set.

Suggested fixes

1. Make the early return conditional on the extension actually providing the classes:

   if (extension_loaded('zvec') && class_exists('ZVecIndexParams')) return;

2. Document the -n requirement in AGENTS.md (Testing Requirements section) so contributors on machines with the old extension don't hit this
3. Long term: ensure the php-ext/ extension build keeps parity with FFI classes or remove it from the test path