Deliver: Program Design Section

[seanrreid]

Closes #79.

Summary

Adds an optional ## Program Design section to the plan template plus an advisory lint nudge when a large plan omits it — surfacing the design layer (signatures, control flow, file-tree delta) most worth reviewing at Gate 1, without ever blocking. Upstreamed from Dex Horthy's Why Software Factories Fail (the "criminally underemphasized" Program Design phase; WSFF arc lead, memory wsff-source-author-update).

• .claude/commands/team/rad-plan.md — optional ## Program Design section in the template (after Files in Scope), naming its three artifacts + a recommended-large/medium, skippable-small note. — f200400
• scripts/lint-plan.sh — advisory WARNING (exit code unaffected) when a plan is large (WAVE_COUNT >= 3 OR any scope path matches RAD_HIGH_RISK_PATTERNS) and lacks the section. Reuses has_section, WAVE_COUNT, and the existing high-risk path_matches loop — no new matcher, REQUIRED_SECTIONS untouched. — 3cc6192

Design decisions

• Advisory, never mandatory — omission is a warning, never an error; deliberately kept out of REQUIRED_SECTIONS.
• Presence check only — the linter greps the ## Program Design header; it does not validate the section's contents (that stays the architect's Gate-1 judgment; documented as a non-goal).
• "Large" = ≥3 waves OR a high-risk path — small plans (1–2 waves, no high-risk path) stay silent, matching the recommended/skippable guidance in the template.

Test coverage

5 new cases in scripts/test-lint-plan.sh (full suite ALL PASS, exit 0; 216/216 harness green, no regression from the backward-compatible write_plan signature extension):

• large-via-high-risk-path + no section → advisory present, exit unchanged
• large-via-3-waves + no section → advisory present
• small (1 wave, non-high-risk) + no section → silent
• large + section present → silent
• boundary: exactly 2 waves → silent

Notes for review

• Dogfooded: the plan for this feature (.agents/plans/program-design-section.md) carries its own ## Program Design section — the plan that introduces the section demonstrates it.
• 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 the plan was correctly non-auto-clearable and went through architect approval.

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