v2.15.0 - Plans are mechanical execution; a surfaced question returns to the decision stage (ADR-0037)

Hardens the plan stage after a real incident in a consumer repo: an agent derived a plan whose tasks included deciding undecided things ("decide X" / "clarify Y") — collapsing the decision and plan lifecycle stages and letting decisions slip through as unreviewed plan steps, bypassing the confirmation guard.

Changed

• ADR-0037 — plans are mechanical execution; a surfaced question returns to the decision stage (idea 0031). Amends ADR-0004. A plan is for mechanical execution only and never contains a decision-making task. If a question surfaces while executing, do not fold the decision into the plan — return to the decision stage: clarify / patch / amend the governing ADR (or open a new one), then resume. That it returns is fixed; which form the return takes (patch, amend, or new ADR) is judgment sized to the question. Landed in the spec Plans bullet, the AGENTS.md derived body, a new "Plans are mechanical execution" bullet in both AGENTS.md checklists (audience-fork delta preserved), and a note in both guides. ADR-0004 stands (amended, not rewritten) with an Amended by: back-link.
• Provenance citations bumped v2.14 -> v2.15 across the three starter/ renderings.

Adopter migration

The plans rule is tightened — internalize it and apply it going forward; there is no artifact back-migration. Re-copy the method-owned set (starter/ -> your docs/) to pick up the sharpened spec bullet, the new agent-checklist bullet, and the guide note; existing plans need no rewrite. Then regenerate docs/overview.md as usual.