Deliver: Premise-Freshness Lint

[seanrreid]

Closes #74.

Summary

Adds a premise-freshness check so a plan anchored to deleted/renamed code is caught before deliver time (the "develop-drift" failure class, upstreamed from BEAKON green-lane criterion 10). Cited path:line anchors, per-task File: paths, and Files-in-Scope entries must exist on origin/<default_branch> — unless the plan itself creates them.

• scripts/lib/plan-paths.sh — three new shared helpers (one source of truth for both consumers): plan_cited_anchors (inline anchor extractor, real-path-shape filtered), plan_created_paths (CREATE-exempt set from the Files-in-Scope table), path_exists_on_ref (existence-only, fail-closed return codes: 0 present / 1 absent / 2 unresolvable ref). — 68152af
• scripts/lint-plan.sh — advisory freshness block (warns, never errors; exit 0 preserved). — b66675f
• scripts/classify-low-risk.sh — Rule 0.5 stale-premise eligibility (any absent non-exempt path ⇒ not-low; a stale-premise plan is never auto-clearable). — 64ac5fa

Design decisions

• No implicit git fetch — both checks query the locally-known origin/<default_branch> ref only, keeping lint-plan.sh offline-pure. An unresolvable ref fails closed (advisory in lint, not-low in classify).
• Existence only — line numbers are never verified (they drift too easily to gate on); the :NNN suffix is stripped before the query.
• CREATE-exemption reads the Files-in-Scope table (col-3 new file / col-4 ^New), since there is no per-task Creates: field.

Test coverage

New co-located tests, all green (216/216 harness + all script suites):

• scripts/test-plan-paths.sh (new) — unit tests for all three helpers incl. suffix-strip, non-anchor rejection, present/absent/unresolvable-ref return codes, created-path detection.
• scripts/test-lint-plan.sh — freshness advisory: existing path (no warn), absent path (warn + exit 0), created-file exempt, exit 0 throughout.
• scripts/test-classify-low-risk.sh — stale premise: all-present stays low, absent ⇒ not-low, created file stays eligible.

Notes for review

• All touched files are RAD self-protected machinery (Self-protection: RAD's own harness/gate/script paths are unconditionally high-risk — no auto-clear path may ever clear a change to itself #73), so this plan correctly trips the self-protected advisory and is non-auto-clearable — it went through architect approval, as designed. The guard flagging its own delivery, working as intended.

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