chore(voyage): release v5.6.0 — /trekexecute loop hardening

Bump plugin.json, package.json, package-lock.json, and the README badge
to 5.6.0; prepend CHANGELOG v5.6.0 entry + README "What's new" block for
the S38 loop-hardening work (machine-verifiable completion gate, bounded
recovery cap hierarchy + global budget, iterations_remaining signal,
fan-out hedge harmonization).

Additive — no breaking change. Canonical node --test stays 756 (0 fail);
version-consistency test green across all five version refs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,27 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## v5.6.0 — 2026-06-20 — `/trekexecute` loop hardening: machine-verifiable completion + bounded recovery
+
+Additive — no breaking change. Hardens the `/trekexecute` execution loop so termination is *machine-verifiable* and recovery is *bounded by an explicit budget*, closing the "runs forever" and "declares done without proof" failure modes. Five focused changes; canonical `node --test` 744 → **756** (0 fail).
+
+### Machine-verifiable completion gate (the headline)
+
+- **Stop-signal contract** — `/trekexecute` reports `completed` only when a machine-checkable contract holds: the Phase 7.5 manifest audit PASSes, the stop signal exits 0, and the success criteria are green. **Hard Rule 18** is promoted from prose guidance to an enforced gate, anchored in the Phase 7.5 audit rather than the model's self-assessment.
+
+### Bounded recovery — cap hierarchy + global budget
+
+- **`TREKEXECUTE_MAX_RECOVERY_ITERATIONS`** — a global recovery-iteration budget (default **25**, env-overridable) sits above the per-step caps as a three-axis cap hierarchy (recovery depth · per-step retry · global budget), codified as **Hard Rule 20**. Stops an unbounded recover→retry→recover spiral that the per-step caps alone could not bound.
+- **`iterations_remaining` signal** — surfaced in the progress schema and the summary JSON, with a deterministic gate cross-check (`iterations_remaining == cap − (recovery_depth + Σ attempts-beyond-first)`) that catches a never-decremented counter. Shape-validated in `lib/.../progress-validator.mjs` (`PROGRESS_ITERATIONS_REMAINING_INVALID`: non-negative integer, additive-optional — never required at top level).
+
+### Doc consistency
+
+- **Fan-out hedge harmonized** — the `CLAUDE.md` design-principle line is aligned to the measured claim (parallel wall-clock + structured artifact handoffs as the load-bearing benefit; main-context relief stays explicitly *not demonstrated*), with a banned-phrase **forward-guard** in `tests/lib/doc-consistency.test.mjs` so the over-claim cannot reappear.
+
+### Release hygiene
+
+- **Version sync** — `plugin.json`, `package.json`, `package-lock.json`, the README badge, and the CHANGELOG top entry all at `5.6.0`, guarded by the version-consistency test in `tests/lib/doc-consistency.test.mjs`.
+
 ## v5.5.0 — 2026-06-18 — Coordinated release: brief framing enforcement (2.2) + W1–W3 narrow wins
 
 The coordinated release held since the framing work. Supersedes the unreleased internal milestones **v5.2–v5.4** (W2 model/effort alignment, W3 guardrail hardening, the Handover-1 public-contract formalization), landing them together with the `brief_version 2.2` schema badge and the W1 narrow wins. **Additive — no breaking change for existing consumers:** every `2.0`/`2.1` brief still validates; the new requirements gate only on briefs that *declare* `brief_version: "2.2"`.