feat: explicit effort-tier model across the design-phase spine

Add a Trivial/Small/Standard tier model so the design ceremony scales to
the change while the evidence gate never does. README gains a canonical
'Sizing the work' table + the non-negotiable rule (verification-gate and
code-review-loop always run); shape-spec gets a Step 0 sizing gate;
write-plan and plan-review state which tier they belong to.

skills/plan-review/SKILL.md

@@ -35,12 +35,18 @@ between `write-plan` and implementation.
 
 ## When NOT to Use
 
-- The plan is for a single-file, single-author change (use code review instead)
+- The change is **Trivial** or **Small** (see README "Sizing the work") — plan-review is a Standard-tier step; smaller changes go straight to implementation and `code-review-loop`
 - A previous plan-review already passed and the plan hasn't changed since
 - You don't have a written plan yet (use `write-plan` first)
 
 ## Process
 
+**Effort tier:** plan-review is a **Standard**-tier gate — it earns its cost when a
+plan carries real design decisions across multiple files. **Trivial** and **Small**
+changes skip it; their safety net is `verification-gate` plus `code-review-loop` on
+the diff, which never skip regardless of tier. Reviewing a one-task plan is the kind
+of ceremony that teaches people to route around the gates that matter.
+
 ### Step 1: Locate and read the plan
 
 **Goal:** Confirm the plan file exists and meets the minimum bar to be reviewed.

skills/shape-spec/SKILL.md

@@ -42,6 +42,31 @@ is written.
 
 ## Process
 
+### Step 0: Size the change
+
+**Goal:** Scale the ceremony to the change before spending it. A full spec on a
+one-line fix trains people to skip the whole discipline; no spec on a multi-module
+change is how the missing constraint ships.
+
+**Actions:**
+
+1. Classify the change (when unsure between two tiers, pick the smaller and say so
+   — the plan contract upgrades it later if the work grows):
+   - **Trivial** — one-line / single-file / describable in one sentence. **Stop
+     here — no spec.** Make the change, then go straight to `verification-gate`
+     and `code-review-loop`.
+   - **Small** — one focused change, ≤ ~3 files, design obvious. **Skip the spec**
+     and hand off to `write-plan` for a lightweight inline plan; `plan-review` is
+     optional at this tier.
+   - **Standard** — multi-file, multi-session, or real design decisions. Continue
+     to Step 1 and write the full spec.
+2. Whatever the tier, the evidence never scales to zero: `verification-gate` runs
+   and `code-review-loop` reviews any shipped diff. Ceremony is what scales, not
+   the gate. (Full tier table: README "Sizing the work".)
+
+**Output:** The chosen tier, stated out loud, and — for Trivial/Small — the handoff
+to the right next step instead of a spec.
+
 ### Step 1: One-line summary
 
 **Goal:** Force the spec into a single sentence before any further work.

skills/write-plan/SKILL.md

@@ -35,12 +35,20 @@ before code or `plan-review`.
 
 ## When NOT to Use
 
-- The change is single-file and you'll finish it in 30 minutes
+- The change is **Trivial** (one-line / single-file / describable in one sentence) — skip planning, make the change, run `verification-gate`
 - A plan exists; you should be running `plan-review` against it, not rewriting it
-- You don't have a spec yet — go to `shape-spec` first
+- You don't have a spec yet and the change is **Standard** — go to `shape-spec` first
 
 ## Process
 
+**Effort tier:** planning is for **Small** and **Standard** changes. A **Small**
+change (≤ ~3 files, obvious design) needs only a lightweight inline plan — the
+task list and per-task acceptance check below, skipping the spec that fed it. A
+**Standard** change gets the full plan and then `plan-review`. **Trivial** changes
+skip this skill entirely. Either way `verification-gate` and `code-review-loop`
+still run — planning scales, the gate does not. (Full tier table: README "Sizing
+the work".)
+
 ### Step 1: Confirm the spec is sufficient
 
 **Goal:** Avoid planning against a spec that itself is incomplete.