preflight branch-freshness check: tolerate transient git-fetch timeouts (#664 false-positive recurrence)

Goal

Make src/explore_persona_space/orchestrate/preflight.py's branch-freshness check tolerate transient git fetch origin timeouts so a slow-network pod is not falsely reported as ok=false. Surfaced as a recurring false-positive during the #664 r9 recovery relaunch (2026-06-28) — the experimenter had to independently re-verify branch currency to push through a transient fetch-timeout ERROR on an otherwise-healthy pod.

Repro

On a freshly-bootstrapped RunPod pod with intermittent outbound HTTPS latency, uv run python -m explore_persona_space.orchestrate.preflight --json reports ok=false with errors: ["git fetch origin failed (timeout) — cannot verify ..."]. Direct git fetch origin issue-664 --depth=1 from the SAME pod completes with rc=0 within seconds; git rev-parse HEAD == origin/issue-664 confirms the branch is up-to-date.

Proposed fix

In the branch-freshness check inside preflight.py:

1. On fetch timeout, retry the fetch ONCE with a longer timeout (e.g. 60s vs the current short timeout).
2. If the retry STILL times out but a prior remote-tracking ref (origin/<branch> from a previous fetch) exists AND behind_count_against_last_known_ref == 0, downgrade the ERROR to a WARNING: "git fetch timed out; last-known origin ref shows branch up-to-date".
3. Keep ERROR semantics only when the branch is verifiably behind OR no last-known ref exists at all.

Acceptance criteria

• Preflight returns ok=true on a pod with a transient fetch timeout AND a verifiably-current checkout against the last-known origin ref.
• A genuinely-stale checkout (or no last-known ref) still reports ok=false with a clear ERROR.
• The retry adds at most ~60s wall-clock to preflight on the slow-network case.
• Unit test added covering both cases (mock fetch timeout + currency-check pass; mock fetch timeout + behind-count > 0).

Out of scope

• Other preflight checks (HF reachability, disk, GPUs) — only the branch-freshness fetch is in scope.
• Removing the branch-freshness check entirely — keep it; just make it timeout-tolerant.

Provenance

Surfaced by the experimenter agent on the #664 recovery relaunch (2026-06-28). Full candidate block in epm:workflow-fix-candidate v1 on task #664. Target file is under src/explore_persona_space/orchestrate/ (not in the named workflow-surface src/ modules), so the proper home is an infra task that PM's auto-dispatch picks up rather than workflow-improver.