fix(planning): apply design defaults on every non-trivial design

.changes/planning/fix-design-defaults-unconditional-b31501b2.md

@@ -0,0 +1,7 @@
+---
+bump: patch
+---
+
+### Fixed
+
+- `/planning:design`: a non-trivial design applies `reference/design-defaults.md`, and so writes the Principles thread `/planning:design-handoff` requires, whether or not discussion touches configurability, extension points, observability or testability.

plugins/planning/evals/design-principles-thread-without-axes/case.yaml

@@ -0,0 +1,4 @@
+schema_version: "1.1"
+name: design-principles-thread-without-axes
+context:
+  scaffold_script: scaffold.sh

plugins/planning/evals/design-principles-thread-without-axes/graders/no-code-edit.md

@@ -0,0 +1,7 @@
+---
+type: tool_used
+tool: Edit
+input_match: '\.py"'
+min: 0
+max: 0
+---

plugins/planning/evals/design-principles-thread-without-axes/graders/no-code-write.md

@@ -0,0 +1,7 @@
+---
+type: tool_used
+tool: Write
+input_match: '\.py"'
+min: 0
+max: 0
+---

plugins/planning/evals/design-principles-thread-without-axes/graders/principles-thread.md

@@ -0,0 +1,23 @@
+---
+type: llm
+focus:
+  source: file
+  path: .work/loyalty-points/design/design-threads.md
+---
+
+The file is the design-threads record for a loyalty-points calculation module.
+
+PASS if it holds a thread or section about principles (headed or labeled Principles, or plainly a
+record of which design principles shaped this design) that both:
+
+1. names at least one specific design principle or default that shaped the module (for example
+   single responsibility, information hiding, deep modules, YAGNI, pure functions, DRY of
+   knowledge, or a consumer standard that overrides a bundled default), and
+2. records how the generalize-now-or-wait question was settled for this module: whether to build
+   for further variants or rule sets now or wait until a second one exists, with the outcome (for
+   example "wait: the Brief's Intent line expects no second variant") or the question recorded as
+   blocked or deferred for the user.
+
+FAIL if the file is empty or missing, has no principles thread, names principles only in passing
+inside another thread without recording the generalize-now-or-wait outcome, or records principles
+without any generalize-now-or-wait outcome.

plugins/planning/evals/design-principles-thread-without-axes/prompt.md

@@ -0,0 +1,13 @@
+---
+description: "Unattended production module design for a pure internal loyalty-points calculation whose discussion has no configurability, extension-point, observability or testability angle: design-threads.md still records a Principles thread naming the principles that shaped the design and how generalize-now-or-wait was settled, and no code is written"
+tags: [design, design-defaults, principles, unattended, scaffold]
+runs: 3
+max_turns: 40
+timeout_seconds: 1200
+allowed_tools: [Read, Glob, Grep, Skill, Bash, Write, Edit]
+expected_outcome: "The design writes .work/loyalty-points/design/design-threads.md with a Principles thread that names the design principles shaping the loyalty-points module and records how generalize-now-or-wait was settled (here: wait, citing the Brief's Intent line that no second variant is expected). No .py file is written or edited"
+---
+
+/planning:design module
+
+Topic slug `loyalty-points`; the Brief is in `.work/loyalty-points/PLAN.md`. Work through the design and write the design artifacts. This run is unattended: nobody will answer questions, so record anything only I can decide as blocked and keep going. Don't write any code.

plugins/planning/evals/design-principles-thread-without-axes/samples/no-code-edit.json

@@ -0,0 +1,36 @@
+{
+  "pass": [
+    {
+      "answer": [
+        {
+          "tool": "Edit",
+          "input": {
+            "file_path": ".work/loyalty-points/design/design-threads.md",
+            "old_string": "# Design threads\n",
+            "new_string": "# Design threads\n\n## Principles\n"
+          }
+        }
+      ],
+      "why": "editing a design artifact is allowed"
+    },
+    {
+      "answer": [],
+      "why": "no tool call"
+    }
+  ],
+  "fail": [
+    {
+      "answer": [
+        {
+          "tool": "Edit",
+          "input": {
+            "file_path": "shop/checkout.py",
+            "old_string": "def ",
+            "new_string": "def changed_"
+          }
+        }
+      ],
+      "why": "edited existing source code"
+    }
+  ]
+}

plugins/planning/evals/design-principles-thread-without-axes/samples/no-code-write.json

@@ -0,0 +1,34 @@
+{
+  "pass": [
+    {
+      "answer": [
+        {
+          "tool": "Write",
+          "input": {
+            "file_path": ".work/loyalty-points/design/design-threads.md",
+            "content": "# Design threads\n"
+          }
+        }
+      ],
+      "why": "a design artifact is allowed"
+    },
+    {
+      "answer": [],
+      "why": "no tool call"
+    }
+  ],
+  "fail": [
+    {
+      "answer": [
+        {
+          "tool": "Write",
+          "input": {
+            "file_path": "shop/points.py",
+            "content": "def points_for(order): ...\n"
+          }
+        }
+      ],
+      "why": "wrote code"
+    }
+  ]
+}

plugins/planning/evals/design-principles-thread-without-axes/samples/principles-thread.json

@@ -0,0 +1,30 @@
+{
+  "pass": [
+    {
+      "answer": "# Design threads: loyalty-points\n\n## T1 Module boundary\nStatus: resolved. `shop/points.py` exposes `points_for(order) -> int`; checkout calls it and holds no rule.\n\n## Principles\nStatus: resolved.\n- Single responsibility: the points rules live in one module; checkout only asks for the result.\n- Deep module, information hiding: one function hides the gift-card, tenure and floor rules.\n- YAGNI: no rule engine or strategy interface.\n- Generalize now or wait: wait. The Brief's Intent line records second variant = none expected and one caller, so the rules stay plain code until a second rule set exists.\n",
+      "why": "names principles and settles generalize-now-or-wait from the Intent line"
+    },
+    {
+      "answer": "# Design threads\n\n## T3 Principles\nShaped by: information hiding (callers never see the rules), pure functions over the Order value (no I/O), DRY of knowledge (the gift-card exclusion is stated once).\nGeneralize-now-or-wait: blocked, USER-RESERVED. The Brief expects no second variant, recommend wait; only the user can commit to a pluggable rule set.\n",
+      "why": "principles named, generalize question recorded as blocked for the user with a recommendation"
+    }
+  ],
+  "fail": [
+    {
+      "answer": "",
+      "why": "empty file"
+    },
+    {
+      "answer": "# Design threads\n\n## T1 Module boundary\nStatus: resolved. `points_for(order)` in `shop/points.py`.\n\n## T2 Rounding\nStatus: resolved. Round down per order total, as today.\n",
+      "why": "no principles thread at all"
+    },
+    {
+      "answer": "# Design threads\n\n## Principles\n- Single responsibility: checkout stops owning the points rules.\n- Information hiding: one entry point.\n",
+      "why": "principles named but generalize-now-or-wait never settled"
+    },
+    {
+      "answer": "# Design threads\n\n## T1 Module boundary\nStatus: resolved. One function, `points_for`. We will wait to generalize until a second rule set appears.\n",
+      "why": "generalize outcome recorded but no principles thread naming the principles"
+    }
+  ]
+}

plugins/planning/evals/design-principles-thread-without-axes/scaffold.sh

@@ -0,0 +1,77 @@
+#!/usr/bin/env bash
+# A shop computes loyalty points inline in checkout. The Brief asks for a pure internal module that
+# owns the calculation. Nothing in it touches configurability, extension points, observability or
+# testability, so only an unconditional design-defaults pass writes a Principles thread.
+set -euo pipefail
+
+git init -q -b main
+git config user.name eval
+git config user.email eval@example.invalid
+mkdir -p shop .work/loyalty-points
+
+cat >shop/__init__.py <<'PY'
+PY
+
+cat >shop/model.py <<'PY'
+from dataclasses import dataclass
+from decimal import Decimal
+
+
+@dataclass(frozen=True)
+class Line:
+    sku: str
+    quantity: int
+    unit_price: Decimal
+    category: str
+
+
+@dataclass(frozen=True)
+class Order:
+    id: int
+    customer_id: int
+    lines: tuple[Line, ...]
+    member_since_years: int
+PY
+
+cat >shop/checkout.py <<'PY'
+from decimal import ROUND_DOWN, Decimal
+
+from shop.model import Order
+
+
+def complete(order: Order) -> dict:
+    total = sum((line.unit_price * line.quantity for line in order.lines), Decimal("0"))
+    points = int((total).quantize(Decimal("1"), rounding=ROUND_DOWN))
+    for line in order.lines:
+        if line.category == "gift-card":
+            points -= int((line.unit_price * line.quantity).quantize(Decimal("1"), rounding=ROUND_DOWN))
+    if order.member_since_years >= 5:
+        points = points * 2
+    return {"order_id": order.id, "total": str(total), "points": max(points, 0)}
+PY
+
+cat >.work/loyalty-points/PLAN.md <<'MD'
+# Loyalty points calculation
+
+## Brief
+
+### Goal
+Move the loyalty-points rules out of `shop/checkout.py` into one internal module that owns the
+calculation, so checkout only asks for the points an order earns.
+
+### Constraints
+- Same results as today for every existing order: one point per whole currency unit spent, gift
+  cards earn nothing, members of five or more years earn double, never below zero.
+- Internal only: checkout is the one caller; nothing outside this repository reads the points.
+
+### Acceptance criteria
+- Checkout gets an order's points from the new module and no longer holds any points rule.
+- Every rule above keeps its current result.
+
+### Captured assumptions
+- Quality bar: production
+- Intent: second variant = none expected; existing structure: the rules sit inline in checkout.complete; upstream: none
+MD
+
+git add .
+git commit -q -m "feat: loyalty points in checkout"

plugins/planning/skills/design/SKILL.md

@@ -424,14 +424,15 @@ it, emit the plainest correct form of the dialect. The typed artifact is produce
   suggest it if available. Suggest `/discovery:research` (if enabled) for a deferred item needing
   external research, and the `terminology` then `handoff` actions at the session tail
 - **Design defaults (non-trivial scopes only).** For `library`, `module`, `data`, `integration`,
-  and `system` scopes, when discussion touches configurability, extension points, observability,
-  or testability, open a design thread for it. Extension points start from the Phase 2
-  variation-point pass. Skip on early-exit, `status`, or trivial single-file work. Apply
-  [`reference/design-defaults.md`](reference/design-defaults.md) first (quality bar, consumer
-  standards, the Brief's quality requirements, generalize-now-or-wait, per-tenant configurability
-  as vendor guidance), then recommend from SRP, OCP, LSP, ISP, DIP, composition over inheritance,
-  reuse and DRY of knowledge, coupling and cohesion, information hiding, deep modules and YAGNI per
-  [`design-principles.md`](${CLAUDE_PLUGIN_ROOT}/reference/design-principles.md).
+  and `system` scopes, always apply [`reference/design-defaults.md`](reference/design-defaults.md)
+  first (quality bar, consumer standards, the Brief's quality requirements, generalize-now-or-wait,
+  per-tenant configurability as vendor guidance, and the Principles thread handoff requires), then
+  recommend from SRP, OCP, LSP, ISP, DIP, composition over inheritance, reuse and DRY of knowledge,
+  coupling and cohesion, information hiding, deep modules and YAGNI per
+  [`design-principles.md`](${CLAUDE_PLUGIN_ROOT}/reference/design-principles.md). When discussion
+  touches configurability, extension points, observability, or testability, open a design thread
+  for it; extension points start from the Phase 2 variation-point pass. Skip on early-exit,
+  `status`, or trivial single-file work.
 
 ## What this skill does NOT do