docs(voyage): S15 — cost-claim truth-pass + premium default-profile pins

Resolve the S14 default-profile contradiction. Investigation overturned
the audit addendum's guess ("code is the bug → balanced"): commit 40d8742
(2026-05-13, "pin all sub-agents to Opus permanently (operator request)")
plus VOYAGE_PROFILE=premium in ~/.zshenv establish premium as the deliberate
default. Operator confirmed in-session: premium is the shipped default; fix
the stale docs, not the code. No code or behaviour changed (lib/ untouched).

Docs (default-name → premium, consistent across resolver + all three docs):
- README + docs/profiles.md + docs/operations.md: 3 lookup-order sites and
  3 profile tables now mark `premium` as the default.
- premium table row corrected to all-opus (matches premium.yaml — a third
  inconsistency the audit missed; README/profiles.md showed opus/sonnet/...).

Cost narrative made honest (premium = all-Opus reality):
- §Cost profile rewritten: uniform model per phase, no orchestrator-vs-swarm
  split; cheaper via --profile balanced/economy.
- Removed false "Sonnet exploration/review swarm" claims (README 195/223/266
  model-neutral; 804 parenthetical; the "Switch the planning model" note).
- profiles.md custom-profile prose corrected: built-in wins over same-named
  custom (findProfilePath), dropping the bogus "balanced is the locked default".

Pins (TDD red→green, doc-consistency.test.mjs):
- default-profile name invariant (resolveProfile ↔ README/profiles/operations)
- profile tables ↔ each built-in yaml phase_models (structural, catches drift)
- cost-claim regression guard (no resurrected Sonnet-swarm phrasing)

S16/S18 surface untouched: counts (23 agents, 9/10 dims, 5/6 dims), versions,
framing gates unchanged. Full suite 686 (684 pass / 2 skip / 0 fail).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LqBYc8Ltrk7LipyJmGxXiB

docs/profiles.md

@@ -12,13 +12,17 @@ Three pre-defined tiers ship with v4.1, located at
 | Profile | Brief | Research | Plan | Execute | Review | Continue | Use case |
 |---------|-------|----------|------|---------|--------|----------|----------|
 | `economy` | sonnet | sonnet | sonnet | sonnet | sonnet | sonnet | Lowest cost; small-scope tasks where you have high confidence the brief is right |
-| `balanced` (default) | sonnet | sonnet | opus | sonnet | opus | sonnet | Default — opus where reasoning depth pays off (plan synthesis + adversarial review) |
-| `premium` | opus | sonnet | opus | sonnet | opus | sonnet | Critical-path planning + review when budget allows |
+| `balanced` | sonnet | sonnet | opus | sonnet | opus | sonnet | Mixed — opus where reasoning depth pays off (plan synthesis + adversarial review); opt-in via `--profile balanced` |
+| `premium` (default) | opus | opus | opus | opus | opus | opus | Maximum quality — Opus on every phase + external research on (default since the 2026-05-13 operator decision) |
 
-`balanced` is the v4.1 default. It puts opus on the two phases where
-quality matters most (Plan synthesis + Review) and sonnet everywhere
-else. This lands the cost/quality trade-off that solo-developers and
-small teams actually want.
+`premium` is the default tier — set by the 2026-05-13 operator decision and
+matched by the hardcoded resolver default in `lib/profiles/resolver.mjs`. It
+runs opus on every phase and turns external research on: maximum quality, at
+roughly 5× the sub-agent cost of an all-sonnet run, accepted as a deliberate
+trade-off. Drop to `--profile balanced` (opus only on the two phases where
+quality matters most — Plan synthesis + Review — and sonnet everywhere else)
+or `--profile economy` (sonnet everywhere) when cost or latency matters more
+than depth.
 
 `economy` is *strictly experimental* in v4.1. The cross-tier Jaccard
 floor (0.55) is grounded in parked-synthetic fixtures, not empirical
@@ -92,7 +96,7 @@ Voyage resolves the profile in this priority order:
 2. **Plan-file frontmatter `profile:`** — when resuming via
    `/trekexecute --resume` or `/trekcontinue`
 3. **`VOYAGE_PROFILE` environment variable** — useful for headless CI
-4. **Default `balanced`** — final fallback
+4. **Default `premium`** — final fallback
 
 The resolved value is recorded in two places:
 
@@ -116,10 +120,10 @@ The validator (`lib/validators/profile-validator.mjs`) enforces:
   one of the canonical short names
 - All six phases must be present (no partial profiles)
 
-Custom profiles override built-ins of the same name (lookup is
-alphabetical with `<custom>` taking precedence). You may NOT redefine
-`balanced` (the default tier is locked to prevent accidental override
-of headless CI behaviour); use a different name and reference it via
+The three built-in names (`economy`, `balanced`, `premium`) resolve to their
+bundled yaml first — `findProfilePath()` returns the built-in before consulting
+`voyage-profiles/`, so a same-named custom file is ignored and cannot shadow a
+built-in. To customize, give your profile a new name and reference it via
 `--profile <new-name>` or `VOYAGE_PROFILE=<new-name>`.
 
 ### Example custom profile