Addresses bot review on #5434:
* Narrow `_ensure_flash_linear_attention` from `_model_wants_causal_conv1d`
(which also matches Nemotron-H / Falcon-H1 / Granite-H / LFM2) to
`_model_wants_tilelang` (Qwen3.5 / Qwen3.6 / Qwen3-Next only). True
SSM families take the mamba_ssm path and never call FLA's GDN
kernels, so installing FLA there is wasted bandwidth.
* Pin both `flash-linear-attention==0.5.0` and `fla-core==0.5.0` and
install with `--no-deps`. Otherwise pip resolves fla-core's
declared `torch>=2.7.0` requirement and may silently upgrade the
Studio venv's torch on environments running torch 2.4/2.5/2.6.
* Skip both installs on Python <3.10 (FLA, fla-core, and tilelang
all declare `Requires-Python: >=3.10`). On older interpreters the
pip install would fail every launch and leave the worker on the
slow torch fallback while still claiming to have set up the fast
path.
* Skip tilelang install on non-Linux platforms. `tilelang==0.1.8`
only publishes Linux x86_64 / aarch64 and macOS arm64 wheels.
Falling back to its 93MB sdist on a Studio worker is undesirable.
* Detect an existing `apache-tvm-ffi` 0.1.10 / 0.1.11 install and
force a reinstall to 0.1.9 with `--force-reinstall --no-deps`.
Previously the import-only probe returned early and left the
broken version in place, which crashes Triton on sm_100.
* Add a 600s timeout to the tilelang and FLA subprocess.run calls,
matching the existing flash-attn install pattern, so a network
hang cannot block the training subprocess indefinitely.
* 13 new / updated tests covering all six guards plus the
pinned-spec, timeout, and force-reinstall code paths.
Total: 21 passing tests (8 original + 13 new / updated).
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