Helix not sending completion event to LSP on backslash

[vglfr]

I am trying to make simple completion lsp use backslash for latex-style expansion, e.g. \lambda should be replaced with λ.

While typing a character Helix sends didChange event to LSP immediately followed by completion:

2025-02-11T19:13:30.121 helix_lsp::transport [INFO] scls -> {"jsonrpc":"2.0","method":"textDocument/didChange","params":{"contentChanges":[{"range":{"end":{"character":0,"line":0},"start":{"character":0,"line":0}},"text":"f"}],"textDocument":{"uri":"file:///home/vglfr/test/agda/tmp.rs","version":95}}}
2025-02-11T19:13:30.372 helix_lsp::transport [INFO] scls -> {"jsonrpc":"2.0","method":"textDocument/completion","params":{"context":{"triggerKind":1},"position":{"character":1,"line":0},"textDocument":{"uri":"file:///home/vglfr/test/agda/tmp.rs"}},"id":22}

However on \ character only didChange event is sent so completion has to be forced with C-x.

Why is that?