fix(#432): setup_log_file temp fallback so prepare-host never bare-fails on an NFS home

[shujaatTracebloc]

#432 — network-FS guard runs before the log dir is created

Most of #432 already shipped in #441 (commit dacba26, "run the network-FS guard before the log dir is created"): early_data_dir_guard now runs before setup_log_file in the full install, and validate_config (before it) only validates — it never mkdirs. That path is done, with a #432 ordering test already in preflight.bats.

This PR closes the one path #441 didn't cover: prepare-host.main() calls setup_log_file on the prepare-host branch before any guard, and setup_log_file did a bare mkdir -p "$HOST_DATA_DIR" + tee. On an NFS home under sudo + root_squash — the exact scenario #432 names — that failed with a cryptic mkdir/tee error before any friendly message (or landed the log nobody-owned).

Fix:setup_log_file now picks its path via a small, testable _choose_log_file — HOST_DATA_DIR when it's creatable and writable, else a temp file (the scope's "start logging in a temp location" option). No install path dies on a bare mkdir/tee anymore. The full install's early_data_dir_guard still refuses a network data dir before this runs, unchanged. (The temp template uses trailing X's — BSD mktemp on macOS rejects a suffix after XXXXXX.)

Acceptance

• NFS-home + root_squash machine reaches the guard's friendly, named error (full install, via fix(installer): run the network-FS guard before the log dir is created #441) — and the prepare-host path no longer hits a prior bare mkdir/tee failure or mis-owned files (this PR).

Tests

_choose_log_file: returns a path under a writable HOST_DATA_DIR; falls back to a temp path (never a bare failure) when the dir is uncreatable/unwritable. shellcheck --severity=error + check-style + check-drift clean; scripts/manifest.sha256 regenerated (R8).

Note: two suites carry a pre-existing macOS-only failure on clean develop (validate_config: valid config passes, early bailout: healthy tracebloc doctor) — unrelated to this change (they pass on the Linux CI leg).

Closes#432

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Note

Low Risk
Small, defensive change to installer logging path selection with unit tests; no change to full-install guard ordering or cluster/data semantics.

Overview
setup_log_file no longer assumes HOST_DATA_DIR is creatable. A new _choose_log_file helper tries mkdir -p plus a write probe under HOST_DATA_DIR; if that fails, it uses mktemp with a BSD-safe XXXXXX suffix (no .log after the X’s), or /dev/null as last resort. setup_log_file only sets LOG_FILE from that helper and then tees as before.

This closes the prepare-host gap left after #441: that path calls setup_log_file before any network-FS guard, so NFS home + sudo + root_squash used to die with a cryptic mkdir/tee error (or mis-owned logs) instead of continuing to user-facing errors. The full install’s early_data_dir_guard ordering is unchanged.

Bats cover writable vs uncreatable HOST_DATA_DIR; scripts/manifest.sha256 is updated for common.sh.

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[LukasWodka]

/fr-pass