Summary

Closes #1100. Part of the guided Hal0 Installer Setup redesign (Wave 2 / WS-D, decision Q4). Extends #1095's _persist_store_dir() (which threads Selections.storage_dir into [models].store) to also handle the FLM/NPU side of the store:

• Setting the model store now seeds [models].store and co-locates [models].flm_store at <store>/flm/models (the convention already documented on ModelsConfig.flm_store and used by installer/install.sh), so NPU weights no longer strand on the root filesystem when --models-dir is set.
• Added a non-fatal writability + free-space check (_validate_store_mount) on the chosen mount: warns (log only, never raises) when the mount isn't writable, sits on the root filesystem, or has less than 10 GiB free — mirroring the ancestor-walk pattern in cli.setup_plan._free_space_gib without importing from it (isolation guardrail — that file is owned by a sibling workstream).
• Idempotent: skips the rewrite only when both [models].store and the co-located [models].flm_store already match; a config that pre-dates this change (store set, flm_store empty) still gets the co-located value seeded on the next persist.
• Best-effort per ADR-0010, matching installer-setup WS-A: honor or remove Selections.storage_dir #1095's existing behavior: empty/relative storage_dir values are ignored, and config-write failures are swallowed so a bad pick never aborts the slot/extension walk.

Files changed

• src/hal0/install/orchestrate.py — _persist_store_dir extended; new helpers _colocated_flm_store, _validate_store_mount, _free_space_gib, _nearest_existing_ancestor, _is_root_fs, _is_writable.
• tests/install/test_orchestrate.py — new coverage for co-location, idempotency (including the pre-installer-setup WS-D: co-locate [models].flm_store + free-space validation on chosen mount #1100-config upgrade path), relative/empty no-ops, and each validation warning branch.

No changes needed in src/hal0/config/schema.py — ModelsConfig.flm_store (with its absolute-path validator and effective_store-style resolution via config.paths.flm_models_dir) already existed and needed no changes.

Test plan

• uv run ruff format src tests — clean
• uv run ruff check src tests — all checks passed
• uv run ruff format --check src tests — 639 files already formatted
• uv run pytest tests/install/test_orchestrate.py -q — 20 passed, 1 skipped (host-topology guard skips when tmp and / share a device, e.g. some sandboxes)
• uv run pytest tests/ -q --ignore=tests/e2e — 4680 passed, 14 failed, 9 skipped, 1 error; confirmed via git stash that the same 14 failures + 1 error pre-exist on main (hermes venv/state-render, comfyui phase4, proxmox host detection, container spec dispatch, config-urls proxy, models-preview, settings-store writability) — unrelated to this change.

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