feat(trekbrief): add fable tier option to Phase 3.5 loop

commands/trekbrief.md

@@ -367,13 +367,14 @@ in the question body so the operator sees why it was picked.
 ### The loop — 4 tier-coupled AskUserQuestion calls
 
 Loop over `[research, plan, execute, review]` in order. For each phase,
-issue one `AskUserQuestion` with 3 options:
+issue one `AskUserQuestion` with 4 options:
 
 | Option | Maps to phase_signals entry |
 |--------|----------------------------|
 | **Low effort** | `{phase: <name>, effort: low, model: sonnet}` |
 | **Standard (default)** | `{phase: <name>, effort: standard}` *(model omitted — composition falls through to profile)* |
 | **High effort** | `{phase: <name>, effort: high, model: opus}` |
+| **Fable (max quality)** | `{phase: <name>, effort: high, model: fable}` |
 
 The proposed tier per phase (from the default-derivation heuristic) MUST be
 labelled `(default)` in the option list so the operator can one-click
@@ -384,6 +385,15 @@ The mapping table is canonical:
 - `low → {effort: low, model: sonnet}` (force sonnet for the low-cost path)
 - `standard → {effort: standard}` (model omitted; composition rule resolves via profile)
 - `high → {effort: high, model: opus}` (force opus for the high-confidence path)
+- `fable → {effort: high, model: fable}` (force Fable 5 for the max-quality path)
+
+The fable tier reuses `effort: high` semantics — full swarm, contrarian +
+gemini always-on; `EFFORT_LEVELS` is unchanged (Voyage effort is orchestration
+shape, not model reasoning effort). Model reasoning effort is inherited from
+the session: Fable 5's default effort is `high`, NOT xhigh. To run xhigh, the
+operator sets it at session level via `/effort xhigh`, the `effortLevel`
+setting, or `CLAUDE_CODE_EFFORT_LEVEL` — switching model resets effort to the
+model default, so it does not follow the model.
 
 ### Force-stop handling
 
@@ -891,7 +901,7 @@ Never let stats failures block the workflow.
 ## Profile (v4.1)
 
 Accepts `--profile <name>` where `<name>` is one of `economy`, `balanced`,
-`premium`, or a custom profile under `voyage-profiles/`. Default: `premium`.
+`premium`, `fable`, or a custom profile under `voyage-profiles/`. Default: `premium`.
 
 Resolution order (per `lib/profiles/resolver.mjs`):
 1. `--profile` flag (source: `flag`)

templates/trekbrief-template.md

@@ -17,8 +17,9 @@ source: {interview | manual}
 # plan polishing a wrong premise after a rejected iteration).
 framing: {preserve | refine | replace | new-direction}
 # v5.1 — per-phase effort + model signal (Phase 3.5).
-# `effort` ∈ {low, standard, high}. Omit `model:` for `standard` so composition
-# falls through to profile resolver. Force-stop alternative is the commented
+# `effort` ∈ {low, standard, high}; `model` ∈ {sonnet, opus, fable} (v5.9).
+# Omit `model:` for `standard` so composition falls through to profile
+# resolver. Force-stop alternative is the commented
 # `phase_signals_partial: true` below (mutually exclusive with `phase_signals`).
 phase_signals:
   - phase: research

tests/commands/trekbrief.test.mjs

@@ -16,6 +16,7 @@ import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { resolvePhaseSignal } from '../../lib/profiles/phase-signal-resolver.mjs';
 import { validateBriefContent, PHASE_SIGNAL_PHASES, EFFORT_LEVELS } from '../../lib/validators/brief-validator.mjs';
+import { BASE_ALLOWED_MODELS } from '../../lib/validators/profile-validator.mjs';
 import { parseDocument } from '../../lib/util/frontmatter.mjs';
 
 const HERE = dirname(fileURLToPath(import.meta.url));
@@ -84,8 +85,8 @@ test('trekbrief — SC1: each of 4 phases has both effort AND model on full-sign
     assert.ok(EFFORT_LEVELS.includes(r.effort),
       `phase=${phase}: effort "${r.effort}" not in EFFORT_LEVELS`);
     if ('model' in r) {
-      assert.ok(['sonnet', 'opus'].includes(r.model),
-        `phase=${phase}: model "${r.model}" not in [sonnet, opus]`);
+      assert.ok(BASE_ALLOWED_MODELS.includes(r.model),
+        `phase=${phase}: model "${r.model}" not in [${BASE_ALLOWED_MODELS.join(', ')}]`);
     }
   }
 });
@@ -99,6 +100,19 @@ test('trekbrief — SC1: missing phase_signals + brief_version 2.1 triggers BRIE
   );
 });
 
+// --- v5.9 — fable tier option in the Phase 3.5 loop ---
+
+test('trekbrief — v5.9 Phase 3.5 canonical mapping contains the fable row and offers 4 options', () => {
+  const text = read();
+  const startIdx = text.indexOf('## Phase 3.5');
+  assert.ok(startIdx >= 0, 'Phase 3.5 not found');
+  const section = text.slice(startIdx, text.indexOf('## Phase 4', startIdx));
+  assert.ok(section.includes('fable → {effort: high, model: fable}'),
+    'Phase 3.5 canonical mapping must contain the fable tier row');
+  assert.ok(section.includes('with 4 options'),
+    'Phase 3.5 loop must offer 4 options (AskUserQuestion maxItems: 4)');
+});
+
 // --- v5.5 — framing enforcement + TL;DR + memory-alignment prose-pins ---
 
 test('trekbrief — v5.5 Phase 2.5 framing declaration heading present', () => {