Sparse overlay leaks host lookup errno as a worker crash

[chubes4]

Problem

Filesystem probes against an invalid host path, such as a filename longer than the platform component limit, crash a sparse-overlay fresh worker with a raw Node exception:

ENAMETOOLONG: name too long, lstat ...
    at sourcePath
    at overlay.node_ops.lookup
    at FS.lookupNode
    at faccessat

PHP should receive normal filesystem errno semantics so functions such as file_exists() can return false and callers can handle the path. Standard NODEFS translates host exceptions through NODEFS.tryFSOperation().

Root cause

createOverlayNodeFsMountHandler().node_ops.lookup() calls sourcePath() and NODEFS.getMode() outside NODEFS.tryFSOperation(). Host errors other than the helper's special-cased ENOENT escape JavaScript and terminate the workload.

Expected behavior

Run the complete overlay lookup inside NODEFS.tryFSOperation() so native ENAMETOOLONG, EACCES, and related lookup errors become Emscripten/PHP filesystem errors.

Reproduction

Inside a sparse overlay mount:

echo file_exists( "/overlay/" . str_repeat( "x", 300 ) ) ? "exists" : "missing";

Expected: missing.
Observed before fix: raw Node ENAMETOOLONG worker crash.

Downstream evidence: the WordPress core wp_tempnam() length tests in the other PHPUnit suite.